4.3: Genetic diversity can arise as a result of mutation or during meiosis

Define the term mutagenic agent [1 mark]

Name the type of mutatino that changed the number of chromosomes in S. townsendii to produce S. angelica. Explain your answer [3 marks]

Name of mutation: Non-disjunction

Explanation: In meiosis (1) chromosomes are not separated OR all chromosomes stay in one cell OR chromosomes do not form homologous pairs (2)

Genetic variation within a species is increased during meiosis by crossing over anf the independent segregation of homologous chromosomes.

Apart from mutation, explain one other way genetic variation within a species is increased [2 marks]

1. Randon fusion of gametes OR random fertilisation

2. Produces new allele combinations OR produces new maternal and paternal chromosome combinations

Give one reason why trout eggs produced by meiosis are genetically different [1 mark]

Independent segregation OR crossing over

Define “gene mutation” and explain how a gene mutation can have:

• no effect on an individual

• a positive effect on an individual

[4 marks]

Definition of gene mutation:

1. Change in the base/nucleotide sequence of chromosomes/DNA

Effects:

2. Results in the formation of a new allele

has no effect because…

3. Genetic code is degenerate so amino acid sequence may not change

mutation is in an intron so amino acid sequence may not change

4. Does change amino acid but no effect of tertiary structure

5. New allele is recessive so does not influece phenotype

has a positive effect because

6. Results in change in polypeptide that positively changes the properties of the protein OR results in a change in polypeptide that positivelt changes a names protein

7. May result in increased reproductive success OR may result in increased survival chances

For all 4 marks, at least one mark must be scored in each section of the answer

Give two differences between mitosis and meiosis [2 marks]

1. Mitosis has one division, meiosis has two

2. Daughtr cells genetically identical in mitosis, they are genetically different in meiosis

referance to “genetically” needed once

3. Two cells produced

4. Diploid to diploid/haploid to haploid in mitosis, diploid to haploid in meiosis

5. separation of homologous chromosomes only in meiosis

6. Crossing over only in meiosis

7. Independent segregation only in meiosis

A change from Glu to Lys at amino acid 300 had no effect on the rate of reaction catalysed by the enzyme. The same change at amino acid 279 significantly reduced the rate of reaction catalysed by the enzyme.

Use all the information and your knowledge of protein structure to suggest reasons for the differences between the ffects of these two changes [3 marks]

Both negatively charged to positively charged in amino acid

Chneg at amino acid 300 does not change the shape of the active site

Amino acid 279 may have been involved in an ionic, disulphide, or hydrogen bond and so the shape of the active site changes OR amino acid 279 may be in the active site and required for binding the substrate

Explain how the chromosome number is hakved during meiosis [2 marks]

1. Homologous chromosomes (pair)

2. One of each (pair) goes to each (daughter) cell/to opposite poles

Describe the process of crossing over and expplain how it increases genetic diversity [4 marks]

1. Mutation/extra chromosome in gamete/egg/sperm (that formed zygote)

2. All cells derived (from a single cell/zygote) by mitosis

OR

3. All cells derived from a single cell/zygote by mitosis

4. Mitosis produces genetically identical cells/a clone

Mark points 1 and 2 OR 3 and 4