Topic 3 - Genetics 🟧five spec points missing🟧

Advantages of asexual reproduction

• Only one parent is needed

• Uses less energy

• Faster - don't need to find a mate

Disadvantages of asexual reproduction

• No variation in population because the offspring are genetically identical to the parent

• Means if the environment changes the whole population is affected - same with disease

Advantages of sexual reproduction

Produces variation in offspring, meaning if the environment changes it is likely that some organisms in the species will have good characteristics to survive - over time this leads to natural selection

Disadvantages of sexual reproduction

• Takes time and energy to find a mate

• Isolated individual can't reproduce

What experiment did Mendel do

• Mendel studied how characteristics are passed on from plant to plant

• In his first experiment, he crossed a tall pea plant with a dwarf pea plant

• in his second experiment, he crossed two tall pea plant offspring

What did Mendel conclude

• Offspring have some characteristics that their parents have because they inherit ‘hereditary units’ from each.

• One unit is received from each parent.

• Units can be dominant or recessive, and cannot be mixed together.

Explain why there are differences in the inherited characteristics as a result of alleles

• Alleles (different forms of the same gene) lead to differences in inherited characteristics.

• This is because different alleles code for different forms of the same protein

• an allele that codes for a damaged form of a protein can cause illness.

Define chromosome

A structure found in the nucleus which is made up of a long strand of DNA.

Define gene

A section of DNA that codes for a protein

Define allele

Different versions of the same gene

Define dominant

An allele that is always expressed, even if the individual only has one copy

Define recessive

An allele that needs two copies to be expressed

Define homozygous

when an individual has two of the same allele for a gene

Define heterozygous

When an individual has two different alleles for a gene

Define genotype

The combination of two alleles that an individual possesses for each gene

Define phenotype

The physical expression of the genotype

Define gamete

An organism’s reproductive cell

Define zygote

A fertilised egg cell

Describe how the sex of offspring is determined at fertilisation

• Men have X and Y chromosomes.

• Women have two X chromosomes.

• XX combination allows female characteristics to develop.

• Equal chances of having boy and girl.

Describe the inheritance of ABO blood groups

• inheritance of blood groups is an example of codominance

• three alleles determine blood group inheritance instead of two

• alleles I^A and I^B are both codominant

• they are both dominant to I^O

• I^A results in production of antigen A in the blood

• I^B results in production of antigen B in the blood

• I^O results in no antigens being produced in the blood

Describe how sex-linked genetic disorders are inherited

• Y chromosomes miss some genes found in the x chromosome.

• This means a man (XY) will have only one allele for some genes on the X chromosome (because those genes are missing on the Y chromosome).

• If the allele for on of these X chromosome genes causes a genetic disorder, the man will develop this.

• The allele a man has in the X chromosome, dominant or not, will always be expressed (since there is only one)

What are most phenotypic features the result of

Most phenotypic features are the result of multiple genes rather than single gene inheritance.

Describe the causes of variation that influence phenotype including genetic variation

• Different characteristics can arise as a result of random mutation, and sexual reproduction

• Random mutation occurs in gametes to produce offspring with brand new characteristics

• Sexual reproduction causes the offspring to have a combination of characteristics from mother and father

Describe the causes of variation that influence phenotype including environmental variation

• Characteristics can also be caused by an organism's environment

• For example a child who does receive adequate nutrition will not grow to their full height

• these changes are not heritable

Outcomes of the Human Genome Project

1. Helped scientists to discover which genes predispose people to certain diseases

• Doctors could provide more specific advice on the best lifestyle and diet to help people delay the onset of diseases, or avoid them entirely

2. allowed doctors to design new dugs specifically tailored to those with genetic variation

3. Finally, allows doctors to identify which faulty alleles cause inherited disorders

There is usually ____ within a population of a species, and  _____

there is usually extensive genetic variation within a population of a species, and these arise through mutations

Do mutations affect the phenotype

• Most genetic mutations have no effect on the phenotype

• Some mutations have a small effect on the phenotype

• It is rare for a single mutation to significantly affect the phenotype

Explain the role of meiotic cell division

• Meiosis produces four daughter cells, each with half the number of chromosomes

• this results in the formation of genetically different haploid gametes

Describe DNA

• A polymer made up of:

  • two strands coiled to form a double helix

  • Strands linked by a series of complementary base pairs joined together by weak hydrogen bonds

  • Nucleotides that consist of a sugar and phosphate group with one of the four different bases attached to the sugar

What is a genome

Entire DNA of an organism

What is a gene

A section of DNA that codes for a specific protein

Explain how DNA can be extracted from fruit

• Mix together water, salt and washing up liquid

• Heat this mixture

• Peel a kiwi and crush with a pestle and mortar

• Add the mixture to the kiwi

• Filter the solution

• Add the filtrate into a test tube

• Add pineapple juice to the test tube and leave it to rest

• Add cold ethanol to the solution and wait

What should be the result of the experiment

• After ten minutes you should see a white mass at the top of the test tube

• This is DNA

Why do you add pineapple juice

• It contains the enzyme bromelain

• Bromelain breaks down proteins attached to DNA

• Means you can see the DNA more clearly

Why do you add ethanol

Causes the DNA to precipitate and become visible at the top of the container

Definition of mutation

Random change to the base sequence of DNA

If there’s no medical treatment for a fatal inherited condition, what will happen to the frequency of alleles

• Frequency of alleles will decrease

• Because individuals affected will die + won’t have children

• This means the allele is not passed on to offpsring

What causes a protein to fold incorrectly

a mutation in the coding region of a gene changes the sequence of amino acids

What is the result of a mutation that happens in the non-coding region

• RNA polymerase is unable to bind

• Transcription does not occur

• Protein cannot be produced

What is the result of a mutation that happens in a gene

Amino acid sequence may change, changing protein structure

What are the two steps of protein synthesis

Transcription and translation

Explain transcription

1. RNA polymerase binds to the non coding region of DNA

2. RNA polymerase moves along the DNA, unwinding helix and separating strands

3. Free RNA nucleotides pair u with exposed complementary bases

4. RNA polymerase forms bonds between the free RNA nucleotides, forming mRNA

5. mRNA leaves nucleus and travels to ribosome

Explain translation

1. mRNA leaves nucleus and moves to ribosome

2. Ribosome reads 3 bases at a time

3. tRNA brings amino acids that are specific depending on the anticodon to ribosome

4. tRNA has an anticodon that is complementary to codons on mRNA

5. Amino acids join to form a polypeptide

6. When a stop codon is reached, the polypeptide is complete so it detaches from the ribosome

7. The polypeptide folds up into a unique 3D structure called a protein. Its shape is determined by the order of amino acids

Describe how mRNA is used to make proteins

• By translation

• mRNA leaves nucleus and joins to ribosomes

• tRNA carries amino acids

• tRNA joins to mRNA

• Bases are read in groups of three

• Amino acids are joined together to make polypeptides

Describe how a section of DNA determines the structure of a protein

• Gene codes for protein

• Sequence of bases determines sequence of amino acids

• One codon for one amino acid

• Several amino acids make up a protein

What is the difference between DNA and RNA

DNA

• double strand

• deoxyribose sugar

• T base

RNA

• single strand

• ribose sugar

• U base replaces T