GCSE Biology - Genetics and Biochemistry | Apredebiology.net (2023)


GCSE Biology: DNA, Protein Synthesis and Mutation.

What you need to know:-

  • A gene is a section of DNA that encodes a specific protein.

  • DNA (structure)

  • How the structure of DNA was discovered

  • DNA determines the order of amino acids in proteins.

  • Steps in protein synthesis, including transcription and translation.

  • A certain number of proteins and amino acid sequence.

  • Genetic mutations can be harmful, beneficial or none at all.

  • A gene is a section of DNA that encodes a specific protein.

  • DNA (structure)

Chromosomes and their genes are made up of a molecule called DNA.

[DNA Image]

Each chromosome is a very long, tightly coiled DNA molecule.

What does DNA mean?

DNA stands for deoxyribonucleic acid.

DNA molecules carry the code that controls what cells are made of and what they do.

A piece of DNA is called a gene!

Remember: the alternate form of a gene is called an allele.

Genes code proteins!

Chromosomes and their genes are made up of a molecule called DNA. (deoxyribonucleic acid)

DNA is a macromolecule that contains the code that controls what cells are made of and what they do (the genetic code).

How the structure of DNA was discovered

1952 – Rosalind Franklin and Maurice Wilkins use X-rays to determine that DNA is spiral.

1953 Watson and Crick discovered the structure of DNA...

[photos of key DNA people]


Nucleotides consist of a nitrogenous base, a pentose sugar and a phosphate group.

[Images of nucleotides]

Nucleotides join together to form a chain.

The phosphate group of one nucleotide binds to the sugar of another nucleotide, releasing water...

Phosphodiester bond formation.

[nucleotide splicing image]

The two strands of the helix are loosely held together by hydrogen bonds linking complementary bases to each other; Adenine binds to thymine and guanine binds to cytosine.

Adenine combines with thymine.


Guanine combines with cytosine.

hydrogen bonds

"Weak hydrogen bonds connect bases".

[picture of hydrogen bonds between bases]

Summary: Structure of DNA

  • double strand of nucleotides (complementary)

  • 4 rules A, T, G and C

  • A=T

  • G≡C

  • Both strands are antiparallel.

  • 2 types of links:

    • Weak hydrogen bonds between bases.

    • Strong phosphodiester bonds between backbone sugars and phosphates

[image of DNA structure]

Protein synthesis

1. Steps in protein synthesis, including transcription and translation.

2. A certain number of proteins and amino acid sequence.

What are proteins?

Proteins are polymers (called polypeptides) made of amino acids.

This is determined by the order of the amino acids3D conformational shapeand protein function.

But... how does a cell put the amino acids in the right order...?

Triple Code!

[codon image]

Thus, triplet base codes (codons) are needed to build each amino acid...

These triplet sequences are called CODONS.

Note: CODONES are three base letters that code for amino acids: DNA and mRNA have CODONES!

[DNA image -> mRNA -> codons -> amino acids]

The table below shows the codons and their corresponding amino acids.

This is a short sequence of bases: - AAACACTTGGTCGTG for a section of the insulin molecule. What is the order of the amino acids?

[Insert codon and amino acid table]

  1. AAA = Phe

  2. CAC = value

  3. TTG = Asn

  4. OW = Glu

  5. GTG = Glü

Some amino acids have more than 1 codon. (it is called "degenerate").

DNA and mRNA have start and stop codons.

RNA = ribonucleic acid

1) RNA is found in the nucleus and throughout the cytoplasm.

2) RNA is made up of RNA nucleotides.

3) RNA is single stranded (but has 3 types)


4) All 3 types of RNA are used in PROTEIN SYNTHESIS!

messenger RNA (mRNA)

Simple spiral strands consisting of several thousand nucleotides.

It is produced in the nucleus by DNA transcription.

Contains Triple CODES!

[codon chart image]

[mRNA image - showing codons]

Transfer RNA (tRNA)

A single thread folded in the shape of a cloverleaf.

Different types of tRNA: each contains an amino acid code.

Used in translation.

has an anticodon

[tRNA image]

rybosomalny RNA (rRNA)

Made in the core.

Used in translation - "Protein synthesis"

Remember! Ribosomes are the sites of protein synthesis!

[rRNA image]

What is a transcript?

Transcription is a process involving the transcription (conversion) of genetic information (e.g. GEN) from DNA to RNA.

Transcription can be considered in 3 phases...

  1. initiation

  2. Elongation

  3. End

Transcription can be broken down into stages...

  1. Initiation: RNA polymerase binds to DNA promoter sites.

  2. Elongation: mRNA is "copied" from DNA.

  3. The growing strand of mRNA bulges out of the "transcript bubble".

[image of mRNA in the transcript]

4. Termination: At the end of the gene, the stop codon releases the mRNA and rewinds the DNA.

Before the mRNA leaves the nucleus through the nuclear pores. The non-coding parts (introns) have to be removed… This is called RNA splicing!


Introns are non-coding segments of DNA and mRNA - introns are removed!

(Introns stay INSIDE the nucleus.)

Exons (expressed): These are DNA and mRNA coding segments (EXons leave the nucleus).

[image of introns and exons]

After removing the introns, the mRNA leaves the nucleus through the nuclear pores in the nuclear membrane... The translation goes like this...

What is a translation?

Translation is a step in protein synthesis during which the genetic code carried by mRNA is decoded to produce a specific sequence of amino acids in a polypeptide (protein) chain.

Translation occurs after transcription (during which the DNA sequence is copied (transcribed) into mRNA).

[picture of translation taking place in the cytoplasm of the cell]

Translation can be divided into stages...

1) The mRNA code is used to assemble the amino acids in the correct order.

2) Ribosomes bind to mRNA and allow tRNA to bind.

3) Each mRNA codon corresponds to a specific tRNA anticodon.

4) tRNA molecules bind amino acids

5) Amino acids combine with peptide bonds… forming polypeptides (proteins)!


Genetic mutations can be harmful, beneficial or none at all.

Mutation = change in DNA base sequence.

[mutation diagram]

Mutations change the DNA of an organism ("at a basic level", that is, they affect the rules in some way. There are three types of mutations that can occur…

  1. Substitution

  2. D damage

  3. Addition

Mutations that occur can be:-

  1. Neutral: neither harmful nor beneficial.

  2. Harmful

  3. Beneficial

  • Neutral: neither harmful nor beneficial. It does not affect the structure of proteins.

  • Harmful - changes the structure of proteins and causes harmful effects - including cystic fibrosis.

  • Beneficial - generates an evolutionary advantage - e.g. resistance to antibiotics.

Three types of mutations...

1. Substancemiscience

Substitution occurs when one base is replaced by another.

This changes the codon of the amino acid while the rest of the protein remains unchanged.

If the new amino acid is similar to the original one, then the structure and function of the protein may remain the same.

If the amino acid is very different, then the protein may have a completely different structure or shape.

[picture of substitution mutation]

2. Elimination

When one base is removed from the DNA, all subsequent bases will be shifted down. This means that each subsequent codon changes, resulting in a completely different protein at the end of replication.

The differences that occur in a gene after a deletion depend on where in the gene the deletion occurs. If the deletion occurs near the end of the gene, then the change may be minor. If the change occurs at the beginning of the gene, it will be a much more severe change.

[removal of mutation image]

3. AnnouncementDstan

One base addition [where an additional base is included in the genetic sequence]. Additives have a very similar effect to removal.

[additional image of mutation]

What are the dangers of mutations?

The greatest danger of gene mutations is changing the protein encoded by the gene.


Well, since most proteins in cells are enzymes, and most changes to enzymes stop them from working, mutations can be catastrophic.


Substitutions are the least dangerous type of mutation because sometimes a protein can remain unchanged. (Remember the degenerate code (amino acids have more than one codon). Well, if the substituted base is one that codes for the same amino acid... the protein will stay the same...


You've learned about DNA before, and that DNA contains "codes" that in turn, in the process of protein synthesis (transcription and translation), make proteins... Well, enzymes are proteins... and now you need to know the structure and function of these biological catalysts. !

So what you need to know:-

  • Enzymes as biological catalysts.

  • Enzymes catalyze chemical reactions, e.g. DNA replication, protein synthesis, digestion.

  • Factors affecting enzyme activity.

  • Enzymes are very specific to their substrate.

  • Lock and key hypothesis

  • Enzymes can be denatured

  • enzyme technology

  • Enzymes in food production.

[The practical work you need to do at school/university should include:-

Factors affecting enzyme activity...

Investigate the use of lactase/immobilized enzymes in food production


You previously learned how proteins are made… (transcription and translation)…

So what are proteins?

Protein: comes from the Greek word "proteios", which means 1st place. (because - Proteins make up over 50% of the dry weight of cells - and are ESSENTIAL for almost everything that organisms do (especially when you consider that ENZYMES are proteins!)


Proteins are organic molecules containing

Carbon, hydrogen, oxygen and nitrogen

Proteins perform many important functions, including

  • structural support

  • Storage

  • Signaling

  • Defense

  • Transport

  • Movement

Also likeENZYMESProteins regulate metabolism by regulating chemical reactions in the cell.

Humans have tens of thousands of different proteins... each with a different, specific structure and function. e.g.

Globular proteins: such as ENZYMES, ANTIBODIES and HORMONES

Fibrous proteins: such as keratin and collagen.


Thus, proteins perform a variety of functions:

Enzymes: Generally spherical, due to the tight folding and coiling of polypeptide chains. They are often soluble and play an important role in metabolism... (for example, enzymes hydrolyze (break down) large food molecules (digestive enzymes), while others help make (synthesize) large molecules.

Enzymes as biological catalysts.

  • Enzymes catalyze chemical reactions.

  • Enzymes are very specific to their substrate.

  • Lock and key hypothesis

So enzymes are proteins.

These are very important substances because they control chemical reactions in our body…

Enzymes are called biological catalysts.- substances that accelerate reactions, but do not exhaust themselves.

[image of enzyme and substrate]

Enzyme names usually end in letters."The North American Stock Exchange"For example: -

AmiloNorth American Stock Exchange, protectNorth American Stock Exchangei citizenNorth American Stock Exchange.

Enzymes are specific to what they will catalyze, and enzymes are reusable:

  • DNA/RNA polymerase

  • Sugarcane

  • lactase

  • Maltese

Enzymes act as "biological catalysts": they speed up chemical reactions.

How does an enzyme actually catalyze a chemical reaction?

Enzymes catalyze a chemical reaction by combining with a reactant and speeding up the reaction.

The reagent is called the substrate.

The enzyme has a specific cleft called the active site that helps it recognize its substrate.

Just as a key only fits a specific lock, each enzyme has its own specific substrate. Once the reaction is complete and the required product is produced, the enzyme is released and proceeds to the next reaction.

[video - enzyme basics]

[ESC lock and key removal]

[activation energy diagram image]

There are two main types of enzymes:

1) Those that break down large molecules into smaller ones.

They are very important in digestion. Why?

They are needed to break down large food particles into smaller ones that can be used by our cells.

2) Those that make large molecules from small ones. They are very important for growth and repair.

Enzymatic specificity (enzymes are very specific).

[Attribution of the PDF file...Use the diagram to explain why each enzyme will only catalyze a particular reaction...Enzymes are specific to a particular type of reaction, in which case they will only be able to bind to Substrate A which matches the active site enzyme].

Factors affecting enzyme activity.

may be enzymesdenatured

Many factors affect the functioning of enzymes: you need to know 3 of them...

1) temperature

2) pH

3) Substrate concentration

  1. Temperature

Most enzymes work best at normal body temperature: 37°C

High temperatures usually denature enzymes.

Most enzymes like a near-neutral pH (6 to 8)

Denaturation is defined as a permanent change in the tertiary (three-dimensional) structure of a protein.

When an enzyme is denatured, it can no longer function.

[image/video graphics]

As the temperature increases, the reaction rate increases to a maximum (usually around 40°C). After this point, the reaction speed will slow down.

Q. Why do you think the reaction is faster with increasing temperature? (think of what happens to molecules when they heat up)

A. Particles involved in the reaction will have more kinetic energy as temperature increases, so they will move more and collide more often.

Therefore, enzyme and substrate molecules are more likely to collide or combine with each other (and thus react)

High temperatures denature the enzyme.

Enzymes are proteins. At high temperatures, these proteins begin to break down. This changes the shape of the active site and, as a result, the substrate can no longer fit in it.

When this happens, the enzyme is said to be "denatured". Once the enzyme is denatured, it will not work.

[enzyme denaturation image - diagram explanation]

2. Effect of pH

Enzymes in the human body will function optimally in narrow pH ranges. Changes in pH beyond the optimum for the enzymes will denature the enzymes.

How does pH affect enzyme activity?

The catalytic activity of an enzyme is affected by the degree of acidity or alkalinity of its environment.

Most enzymes work best under neutral conditions. However, some prefer acidic conditions and others prefer alkaline conditions.

[image pH - enzymes]

Like temperature, the active site of an enzyme can change under conditions that are too acidic or too basic.

Q. Explain how pH can slow down a chemical reaction.

A. If the active site of the enzyme is changed (i.e. denatured), then the substrate will no longer be able to bind to the active site of the enzyme. Therefore, no reaction can take place and no product can be formed.

3) Substrate concentration

The more enzyme in the solution, the greater the chance of enzyme-substrate complex formation and the faster the reaction rate will be, up to a maximum when all active sites are fully occupied.

[explanation of images/graphs of substrate concentrations]

The more substrate there is in solution, the greater the chance that the substrate molecule will find the active site, and the faster the rate of reaction will be, up to a maximum when all active sites are fully utilized.

Enzymes lower the activation energy..

Enzymes lower the activation energy of the reaction [activation energy photo/video]

Enzymatic technology and enzymes in food production.

The use of enzymes in the production of sweets...

Q. How do I get a liquid center from a cream egg?

A. Enzymes!

To get the soft centers in chocolates, many manufacturers add an enzyme called invertase (sucrose), which catalyzes the breakdown reaction of the sugar sucrose.

Many confectionery products are made using enzymes, in particular an enzyme called invertase (sucrose). Invertase is produced by yeast and we can use this enzyme.

Invertase/sucrase breaks down sucrose into glucose and fructose monosaccharides.

Enzymes used in the production of vegetarian cheese

Enzymes in cheese production. Cheese is made by the enzyme chymosin.

Chymosin acts on milk; Specifically, the enzyme catalyzes the reactions that cause the milk proteins (called curd) to coagulate and separate from the liquid (whey).

Chymosin was originally obtained from the stomach tissues of calves. However, today the enzyme is made using genetically modified bacteria. The process is more efficient and the product (Chymosin) contains less impurities and functions in a more predictable way.

Enzymes used in biological powder detergents.


Biological washing powders contain enzymes, e.g.:

proteazy- Break down proteins into amino acids

lips– break down fats into glycerol and fatty acids

carbohydrates(e.g. amylase) - breaks down sugars (polysaccharides, e.g. starch) into monosaccharides (e.g. glucose)

Because bio-based laundry detergents contain enzymes (biocatalysts), they work best at "optimal temperatures".

This means they are more effective at lower temperatures, say around 30°C.

This has many other advantages:

  • Less energy used (heats water / creates carbon emissions)

  • Dyes in fabrics are less likely to "run out"

  • Clothes shrink less when washed

Enzymes are very important... and you will learn more about enzymes by learning about the digestive system, e.g. Enzymes that break down carbohydrates (carbohydrases), such as the enzyme amylase found in oral saliva.

[You will also discuss enzymes in a bit more detail as you study/research how enzymes work: i.e.

  • Use of immobilized enzymes.

  • Lactase breaks down the lactose in milk.

  • Pectinase breaks down pectin (sugar found in the cell walls of plants and fruits)

  • Investigate how temperature and pH affect enzyme activity.

GCSE Biology: Genetics - Heredity.

You will need to learn some new key terms used in genetics and know:-

Genes exist in alternative forms.

Monohybrid genetic diagram/Punnett squares and family pedigrees

Calculate and analyze the results of monohybrid crosses

Symptoms of sickle cell anemia and cystic fibrosis

Pedigree analysis to detect genetic diseases.

Human sex is controlled by a pair of chromosomes.

How the sex of the offspring is determined at the time of fertilization (genetic scheme)

How sex-linked genetic diseases are inherited

First you need to summarize cell division, mitosis and meiosis…

on the cell biology page, we discuss the following:-

How do cells divide to become something?

Through a process called… Mitosis!

Somatic (body) cells are described as diploid (Greek for "double").

... you will see it written as "2n"

Mitosis is the normal process of cell division.

In mitosis, chromosomes are copied and shared equally between 2 new daughter cells. ..

...then each mitotic division produces 2 cells...

So... both are diploid and each has exactly the same genes as the mother cell!! Mitosis produces identical cells.

Some cells in the human body are not diploid...

e.g., gametes (sex cells) contain only 1 copy of each gene because they only have 1 set of chromosomes.

These cells are haploid and are formed by a special type of cell division called meiosis.

The male and female gametes come together during fertilization... to form. zygote

This cell then divides by mitosis to form a completely new organism...

You received the chromatid from your father.

And one of your mother's chromatids!

Thus, even if homologous pairs contain the same genes, they do not necessarily carry the same versions of each gene.

Another version of a gene is called an allele.


This is the key to understanding why organisms differ!

Which brings us to the legacy…

Remember… that in all living things, traits are passed down on chromosomes, which the offspring inherits from their parents.

[Picture of Chromosomes - Genes / Alleles]

Thus, even if homologous pairs contain the same genes, they do not necessarily carry the same versions of each gene.

Remember that the other version of a gene is called an ALLELE.

then each chromosome may have a different version of the gene (allele).

"Different versions of a gene encoding different versions of a trait are called ALLELES."

OK, in genetics different genes (alleles) are usually marked with letters, eg Aa.

The capital letter denotes the DOMINANT "A" allele; while a lowercase "a" would indicate a recessive allele.

some key terminology... Terminology is very important! Make sure you study the language of biology - understanding the meaning of a word makes all the difference!

Here are some key terms you should know:-

Heterozygous, homozygous (dominant and recessive), phenotype, genotype, allele, gene

Homozygous (dominant and recessive) and heterozygous...


"Homo" means "same" and zygote refers to the zygote (fertilized cell). So you can think of a homozygous as having 2 letters of the same "letter", such as 2 uppercase "AA" or 2 lowercase "aa".

Now you know that the capital "A" represents a dominant trait…. therefore, 2 capital letters "AA" can now be called homozygous dominant (2 same capital letters, representing a specific trait, e.g. eye color).

One of these A's (genes/alleles) comes from the mother while the other 'A' (gene/allele) comes from the father; therefore, one of the letters represents the "sperm" and its genes, and the other represents the egg. (egg cells) and their genes….

Homozygous individuals are true reproduction. This means that they will always produce offspring with the same phenotype because they do not "hide" the recessive allele.

So what does heterozygous mean?

Well, "hetero" means "different" and "zygote" refers to the zygote (fertilized cell).

So in genetics and when we use letters to represent heritable traits and traits, we can now think of heterozygotes as two different versions of the same letter...so the capital "A" represents the dominant trait and the small "a" represents the recessive trait.

Aa = heterocygoto

Now you know that the "letters" "A" and "a" are different versions of the same gene, or alleles...

so we have:

Homozygous Dominant: 2 of the same capital letters, AA, FF, HH etc… representing the 2 dominant genes inherited from each parent.

Homozygous Recessive: 2 of the same lowercase letters, aa, ff, hh etc… representing the 2 recessive genes inherited from each parent.

Heterozygous: 2 different versions of the same letters, "Aa", Ff, Hh, etc., representing a dominant allele inherited from one parent and a recessive allele inherited from the other parent.

Now that we know what the letters and key terms homozygous dominant, homozygous recessive, and heterozygote mean, we can better understand what Gregor Mendel was doing when he fertilized the pea plants...

Mendelian and monohybrid inheritance: how individual genes are passed on... Medal and his peas...


What is a monohybrid? We can better understand the term this way:-

mono = one

hybrid = inheriting one gene

so, literally, inheriting a gene...

OK, so... Monohybrid (single gene) inheritance is about the inheritance of different alleles BUT in relation to a single gene. (for example, a height gene or a flower color gene)…

...Like Mendel, we'll start with the pea, which has easily observable traits controlled by a single gene;

for example, peas have a gene for growth.

But the growth gene has 2 alleles:

You can represent growth genes/alleles with the letter "H".

Now you will know that the capital "H" (represents the dominant allele, in this case the allele of being tall).

while the lowercase "h" (denotes the recessive allele, in this case the allele because it is short).


Pea plants are diploid and therefore have 2 alleles (corresponding to height). Therefore, there are 3 possible genotypes:

1. A pea plant can have 2 dominant alleles: "TT" which you know is called homozygous dominant (homo = same) (so pea plants can be said to be homozygous for T-height)

2. A pea can have 2 recessive alleles: "tt", which is known as homozygous recessive (homo = same) (so we can say that the pea is homozygous for t - lack of food)

3. Pea could have inherited 1 dominant allele and 1 recessive allele: "Tt", which is known as heterozygous (hetero = different).

However, keep in mind that the dominant allele will "dominate" the recessive allele...so in this case Tt will be high peas.

Note: more key terms!

The letters we used "Tt" is the organism's genotype (the genes inherited by the organism).

However, the appearance of the organisms - for example, the heterozygous "Tt" pea plant looks tall - is their phenotype (the "physical" result or physical representation of the genotype)...

So the genotype is the genetics of the organism...the genes it contains. Letters can be used to represent them, eg the letter "H" for height... HH, gg or Hh.

The phenotype is the physical result - the expression of these genes... for example, if the letter "H" is the dominant gene for a tall plant - you can physically see the organism, in this case the pea is tall. but you wouldn't. I don't know if the pea was heterozygous or homozygous dominant (because you can't see its genes!)

And that's exactly what Mendel was doing! (He wanted to know what genes peas pass on to their offspring after fertilization.)

Remember that pea plants are diploid: they have 2 alleles (for height in this example).

So let's consider what happens when a homozygous dominant plant (TT = tall) is crossed with a homozygous recessive plant (tt = short).

[insert Punnett square]

All tall plant gametes contain the T allele.

All dwarf plant gametes contain the t allele.

These pea plants are mated at fertilization to produce offspring that inherit 1 dominant gene (allele) "T" from the homozygous dominant (tall) plant and 1 recessive allele from the homozygous recessive (short) plant "t". Thus, the genotypes of all offspring after this fertilization must be "Tt" (herozygous). and since the genes/alleles determine the organism's phenotype, we know that all pea plants "look" tall.

So we can say that all the first pea generations (known as the F1 generation) are tall because height is determined by the dominant (T) allele...

However, while all pea plants look identical (and so does the tall parent plant), they are very different in one very important way: they are heterozygous, NOT homozygous!

Remember: the actual appearance of an organism is called the phenotype!

Mendel wanted to know: what happens when 2 of these heterozygous pea plants are fertilized? What will they look like?

So if 2 of these heterozygous plants are crossed, half of the gametes of each parent are T and the other half are t, giving us 4 results with 3 possible genotypes in the second generation (F2)…

genotypy to: -


2. Ach,

3. Hm

4. gg.

[insert Punnett square]

The first 3 genotypes are all tall plants (phenotypically) but the fourth is a short plant (phenotypically). You can say that 75% are tall and 25% are short...

Monohybrid inheritance in humans.

Clear examples of monohybrid inheritance in humans are quite rare, but often involve a genetic disease where people inherit one or more defective alleles.

Genetic diseases are usually recessive; this is because defective alleles that do not produce an important protein can be masked by normal alleles that function correctly.

that is, recessive alleles are dominated (masked) by dominant alleles.

However, conversely, some genetic diseases, such as Huntington's disease, can be caused by DOMINANT ALLEMS. The alleles in question encode the product that is actively causing the harm; Symptoms are not due to one allele not doing its job. These alleles are dominant because the presence of the normal allele cannot mask symptoms.

Some Examples of Monohybrid Inheritance in Humans:-

[insert image/monohybrid inheritance table]

Pedigree analysis (detection of genetic diseases)

Huntington's disease is a rare inherited disease of the nervous system. it is caused by a dominant allele (we will denote this allele with a capital "H"). The recessive allele of this gene can be described by a lowercase "h".

[insert image "Pedigree"]

The diagram shows the inheritance of Huntington's disease in a family.

Use the genetic diagram to show the inheritance of the Huntington's disease allele by the children of parents P and Q.

[images of genetic diagrams]

Q) Explain why none of R's and S's children inherited Huntington's disease.

[insert image for Q above]

A) This does not apply to both parents; They don't have Huntington's disease.

The genotype of the parents is... hh homozygous recessive (therefore neither parent has a dominant "H" gene/allele and therefore cannot transmit the disease).

Calculate and analyze the results of monohybrid crosses

What if both parents are heterozygous? Arrange the results in a Punnett square:-

[insert square Punnett images and explanations]

Monohybrid genetic diagram Punnett squares and family pedigrees…

Cystic fibrosis is a recessive disease. Cross 2 carriers with Ff genotypes

[insert genetic diagram images]

Arrange the results of the genetic cross in a Punnett square:-

[insert Punnett square / straight ratio / %]

You know that meiosis is a special type of cell division that produces gametes (sex cells).

“Meiosis is a special type of cell division in which there are two successive divisions that result in the formation of gametes – sex cells!”

Remember that sperm and egg cells are haploid: they only have "n" half the number of chromosomes.

Meiosis: production of gametes (sex cells)

You also need to know that:-

Human sex is controlled by a pair of chromosomes (X and Y).

How sex of offspring is determined at fertilization (use genetic diagram).

[insert genetic diagram showing X and Y inheritance]

Organize your scores in a Punnett box:-

[insert Punnett square showing X and Y inheritance]

Sex-linked genetic diseases... How sex-linked genetic diseases are inherited...

You already know that a person's sex is determined by the inheritance of the X and Y chromosomes, now you need to know that some genetic characteristics are also "sex-linked", meaning that they are found on one of the sex chromosomes (X or Y). ).

Color blindness is an example of a sex-linked inherited trait... it is caused by a defective allele on the X chromosome...

Because the Y chromosome is smaller than the X chromosome, it carries less sex-linked genetic diseases!

For example, color blindness is much more common in men than women because men only need 1 defective (recessive) allele while women need 2.

[insert images: This genotype is rare, this genotype is more common]

[insert images of a genetic diagram showing the inheritance of color blindness by sex]

[insert square Punnett images of color blindness inheritance - sex linked]

Sex-linked genetic diseases:

Hemophilia (a disease where the blood does not clot properly) is a genetic condition that is inherited in exactly the same way as color blindness.

Hemophilia is inherited and caused by a defective allele on the X chromosome.

Keyword summary/overview:-

Homozygota: -

The pair of alleles for a given trait are the same, e.g.

Homocigoto dominant = HH

homozygota recesywna = hh

Heterozygous: - A pair of alleles causing a given trait; alleles are different, e.g. H.H.


An allele that will always be expressed even if only one of these alleles is present, denoted by a capital letter. e.g. HH or HH. – H (dominant allele – will be expressed)

Recessive: - An allele that will only be expressed if both alleles are of this type, e.g. H.H.

Gene: - A section of DNA that encodes a specific trait or trait.

Allele: - A different form of the gene that encodes a different version of the same trait (ie a different eye color).

Genotype: - Description of a pair of alleles for a given trait.

Phenotype: - Physical expression of alleles.

Let's see how we canconstruct a monohybrid Punnett squaredue to an inherited condition called brachydactyly.

If the brachydactyl (having short fingers) allele isdominant (B)(which actually is!) and allele "Normal length fingers are recessive (b)- So shouldn't the number of people with short fingers in the population increase with each subsequent generation?

Gloomy in time - Almost everyone should have short fingers!?

Let's look at this problem from a very simple Mendelian point of view...

Suppose a heterozygous man (Bb) and a heterozygous woman (Bb) have a child.… which isprobabilitythat his soninherit the short finger allele (B)Remember that short fingers predominate.

Of course, this is easy to consider using a monohybrid Punnett square:LookWatch the video below to see how a simple mono-hybrid Punnett square is made...

(You'll find out why brachydactyly isn't common in the A-level population when you learn about Hardy-Weinberg equilibrium!)

The Human Genome Project.

What you need to know:

Human genome sequencing.

genetic engineering

Advantages and disadvantages of genetic engineering.

Recombinant DNA technology

Agrobacterium tumefaciens: a vector in the creation of transgenic plants

Bacillus thuringiensis: insect resistance genes

Genetic modification of cultivated plants.

What is a genome?

Remember: the genome is all the DNA, and therefore all the genes (alleles) of each cell of a particular organism. Thus, the human genome is all the DNA (genes/alleles) of the chromosomes of our cells that is mapped, identified, categorized and cataloged.

The Human Genome Project began in 1989 using the DNA base sequencing method developed in 1977 by Fredrick Sanger. This method has enabled scientists from all over the world to collaborate. For 13 years, they have been working together at universities and research centers (the project ended in April 2003) to identify all the genes found on human chromosomes.


Scientists have broken chromosomes to extract DNA fragments and produce thousands of copies. Machines called sequencers then displayed the most likely order of the rules. Computers have been used to match the basic sequences of some genes with the proteins they encode.


Well, knowing where genes are located on chromosomes can be very useful. For example, if "defective genes" are known to cause certain genetic abnormalities, there may be an opportunity to replace those defective genes. Accurate diagnosis of some genetic diseases can be very difficult (e.g. Alzheimer's disease). The human genome project, however, may allow scientists to diagnose genetic disorders more accurately, as testing will be much easier.

The project revealed that certain demographics/race groups are more or less susceptible to certain diseases. Understanding chromosomal diseases can help advance pharmacogenomics: the use of an individual's genome to design personalized drug therapies.

In forensics, a "DNA fingerprint" can be used to determine the presence (or absence) of a person at a crime scene. Using biological samples from a crime scene, criminals can "match" the DNA of, among others, Suspect 1, 2, 3, etc., and determine if they were present with near certainty.

All this raises many ethical questions. For example, some people are concerned that understanding/identifying genetic data about ethnicity may result in (actually encourage) discrimination against certain groups of people. Discrimination can come from employers or insurance companies.

For example, employers may discriminate against people who are at higher risk of contracting a particular disease, and life insurance may be impossible (or very expensive) because of the likelihood of a particular disease.

This can generate more stress: knowing or not knowing, having children or not, etc.

genetic engineering

Genetic engineering: extracting a gene from one organism to insert it into another.

Genes can be inserted into animals, plants, microorganisms... So a transgenic organism is an organism whose genome has been inserted with genes from another organism.

What is recombinant DNA?

The combination of a useful gene with a DNA vector is called recombinant (2 (or more) sources of genetic material have been "recombined". We call a recombinant molecule genetically modified. Host cells are the cells into which the genes will be transferred. Therefore, the organism along with host cells has been genetically modified.

Useful genes can be transferred from cells of one type of organism to cells of almost any other type. To do this, the gene must be linked to a piece of DNA called a vector; vectors are usually plasmids found in bacteria, sometimes viruses are used.

How do you make a useful gene a vector?

We use restriction enzymes (sometimes called restriction endonucleases). Restriction enzymes are enzymes that "cut off" genes of interest from longer stretches of DNA. They "cut out" the gene by recognizing certain regions called restriction sites. This results in short, single-stranded base lengths called "sticky ends". By using the same restriction enzymes in the vector, complementary sticky ends will now be exposed. This allows the gene of interest to be inserted into the vector by complementary base pairing. The enzyme Ligase (Ligat means "to stick together") catalyzes the joining process that reassembles the "recombinant" DNA molecule.

ECOR1 is an example of a restriction enzyme that specifically recognizes the GAATTC restriction site. It is a genetic palindrome (same sequence read backwards and forwards). ECOR1 recognizes the sequence and specifically "cuts" between G and A, exposing sticky ends that allow insertion of the gene of interest.

transgenicThe cows (genetically modified cows) have been designed to produce "designer milk". Milk contains more protein (casein), has human antibodies (usually produced in our white blood cells) and is lower in cholesterol. Therefore, transgenic organisms can be of great importance in the production/improvement of all sorts of things that we humans need to maintain good health and development. For example, the insulin gene was introduced into bacteria to produce the hormone on a large scale and treat diabetes.

How has genetic engineering helped people with type 1 diabetes?

Well, in the past, insulin was often extracted from dead animals [p. e.g. pork]. However, human insulin is now produced using transgenic bacteria. This is how:-

The section of DNA encoding insulin is cut by a restriction enzyme (such as ECOR1)

The plasmid (vector) is excised from the bacterial cell using the same restriction enzyme.

The insulin gene is inserted into a plasmid (vector) and reattached by the enzyme Ligase.

The recombinant plasmid (now containing the human insulin gene) is reintroduced into the bacterial cell where it divides (via binary fission). In this way, "clones" of recombinant DNA encoding insulin were created.

Bacteria can be grown on a large scale using fermenters, producing very large amounts of the human insulin gene, ready to be processed and packaged for medical use.

Another example is transgenic rice. The beta-carotene gene was introduced into rice to reduce vitamin A deficiency (which can lead to blindness in children), especially in Africa and Southeast Asia where rice is a staple food.

Plants can also become resistant.to certain factors that would otherwise kill them. For example, crop resistance to herbicides. Herbicides are used to kill weeds, but they also damage crops. Growing herbicide-resistant crops increases crop yields and produces more food.

This is done by locating a resistant site (often a wild plant with a resistant gene). The resistance gene is then 'excised' from the appropriate chromosome and inserted into the 'non-resistant' plant using a vector (often a plasmid from a bacterium). The transgenic plant is now herbicide resistant. As a result, more food is produced because plants do not have to compete with weeds for resources.

How to create a transgenic plant…

Plants (crops) can be transgenic to provide benefits, such as increasing yields, resisting diseases and herbicides, improving taste (for example, introducing flavonoids into tomatoes), etc.

to bacteriaAgrobacterium tumefacienscontains a plasmid called Ti plasmid (Ti stands for cancer causing) that can be used as a vector. The Ti plasmid causes accelerated growth of infected plants, resulting in a nodular mass of solid tissue called crown gall. Small fragments of crown gall can be used to grow new plants whose cells will carry the recombinant Ti plasmid.

The herbicide resistance gene is isolated and "cut" using a restriction enzyme.

Agrobacterium tumefacienshas a plasmid called a Ti plasmid. Which is cut with the same restriction enzyme.

The herbicide resistance gene is inserted into a Ti plasmid and ligated (reattached) to the enzyme Ligase.

The Ti-plasmid, now recombinant, is reintroduced into bacteria (Agrobacterium tumefaciens).

A plant infected with the bacterium produces a crown gall whose cells contain recombinant DNA, a herbicide resistance gene.

Small pieces of gallium are cut to grow (grow) transgenic seedlings with the herbicide resistance gene.

Seedlings grow into mature, herbicide-resistant plants, helping farmers to control weeds more effectively and increase yields.

Another example is Bt crops. Bt cultures use the bacterium Bacillus thuringiensis, which produces a toxin called Bt ICP (Bacillus thuringiensis insect crystal protein). This protein kills a variety of crop pests.

Bt crops are produced in the same way as herbicide-resistant strains: by isolating the gene of interest and using restriction enzymes to "extract" it and inserting it into vectors, using ligase to produce a recombinant DNA molecule.

Although GMOs seem beneficial and bring great benefits to humans, right?

What is your opinion on genetically modified organisms?

Consider the pros and cons. Be a scientist and work with pro-GMO data and compare and contrast with anti-GMO data.

Some ideas to get you started:-

[insert table/image of ideas]


GCSE biology: cloning.

What you need to know:-

Embryonic stem cells can differentiate into all other cell types.

Research on embryonic stem cells

Cloning is an example of asexual reproduction that produces genetically identical copies.

Stages of production of cloned mammals.

Advantages, disadvantages and risks of mammalian cloning.

Stem cells can differentiate (specialize) into different types of cells.

Remember: a fertilized egg divides (by mitosis) to form an embryo.

Embryonic cells start out the same (undifferentiated) and are commonly called embryonic stem cells.

Embryonic stem cells divide to form more stem cells or different types of cells, specialized cells (for example, red blood cells, white blood cells, liver cells, etc.). This process is called differentiation.

Most animal cells lose their ability to differentiate early in development. However, plants never lose this ability. Adult humans only have stem cells in the bone marrow, which are not as versatile as embryonic stem cells because they cannot differentiate into all cell types.

Many people oppose embryonic stem cell research; arguing that human embryos should not be used for experiments, since each of them is potentially human life.

Opponents suggest that science should find alternatives (for example, bone marrow). As a result, the UK has very strict guidelines allowing stem cell research.

Other countries (e.g. Germany: stem cell research is prohibited).

On the other hand, some believe that when embryonic stem cells are used as possible treatments, the "potential" life of the embryos should be more important. It is noted that the embryos used for research usually come from infertility clinics; therefore they are not used and would otherwise be destroyed. Having an unlimited supply of different types of cells can be very attractive, for example, for transplantation into damaged tissue (stem cell therapy).

Currently, the use of adult stem cells is used to treat certain diseases, including Sickle cell anemia (after bone marrow transplant): Remember that the bone marrow contains undifferentiated stem cells that can produce 'new' red blood cells.

It is possible to use stem cells to create specialized cells that can replace damaged or diseased cells (due to infection or trauma). For example, it may be possible to create new heart muscle, which will help people suffering from heart disease. Stem cell therapy is also ideal for Parkinson's disease and diabetes.

It is because of the potential applications of stem cells that this area is of great scientific interest. In addition, scientists experimented with stem cells, extracting them from early embryos and using them to grow new, differentiated and specialized cells. However, before it is possible to understand all the advantages (and disadvantages) of stem cell research, much research is needed, along with careful consideration of the ethical implications. Remember that many people believe that it is unethical to use embryos for scientific research. .

The risks of stem cell therapy may include:

Rejection of the embryonic stem cell. Secondary effects and complications in the recipient. Stem cells can trigger an immune response and even contribute to the development of some cancers. Mutations passed down from adult stem cells that can then become defective (or cancerous).


Asexual reproduction is a form of cloning.

Remember that some organisms can reproduce (via mitosis), e.g. remember strawberry plants that form stolons and develop into new plants.

This was an example of asexual reproduction: since the new plants have exactly the same genes as the parent plant (there is no genetic variation), the plants are clones!

But what about animal cloning?

Well, this is where "we" intervene...


Cloning has many potential applications, for example:

Endangered animals could be cloned in an attempt to help protect these vulnerable species.

Mammalian cloning could help provide organs for transplantation (helping to address the organ shortage). For example, genetically modified pigs are currently being bred that could provide humans with "appropriate" organs. If successful, cloning pigs will be an effective way to meet the need for organ transplants.

Studies of cloned animals could provide a better understanding of developmental embryology and thus help us understand aging and age-related diseases (disorders).

Unfortunately, there are many problems and controversies surrounding animal cloning today.

For example, cloning leads to a reduction in the gene pool, i.e. less genetic variation in a population. This means fewer alleles and more vulnerability for that particular species.

Remember that if a population is closely related (several genetically different alleles) and a new disease emerges, it can potentially wipe out the population. This is because there may not be a "disease-resistant allele" in the population.

Cloning, although a fairly "easy" technique, is associated with problems. The cloning process itself often fails (Dolly's cloning took over 400 attempts). Clones are often born with genetic defects. Cloned animals often have weakened immune systems, making them less healthy and therefore suffering from more diseases.

For example, the cloning procedure often fails to produce a viable clone. Dolly the sheep is the most famous example of a cloned mammal that lived to be only 6 years old (about half the age of many healthy sheep). Dolly had to be put to sleep because she had many age-related problems, including arthritis and lung diseases. Many people believe this is because Dolly (the clone) was cloned from an older sheep; thus it is implied that Dolly's "true age" was much older. However, Dolly may have just been unlucky and naturally succumbed to these diseases.

Monohybrid cross (Punnett square)


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