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

Question 1

Define the term mutagenic agent. (1)

Answer 1

• (A factor that) increases (the rate of) mutations

Question 2

Apart from mutation, explain one other way genetic variation within a species is increased. (1)

Answer 2

• Random fusion of gametes / Random fertilisation

Question 3

Give one reason why trout eggs produced by meiosis are genetically different. (1)

Answer 3

• Independent segregation
• Crossing over

Question 4

Define ‘gene mutation’ and explain how a gene mutation can have:
- no effect on an individual
- a positive effect on an individual (4)

Answer 4

Definition of gene mutation):
- Change in the base/nucleotide (sequence of chromosomes/DNA)
- Results in the formation of new allelle

Has no effect because:
- Genetic code is degenerate (so amino acid sequence may not change)
/ Mutation is in an intron (so amino acid sequence may not change)
- Does change amino acid but no effect on tertiary structure
- (New allele) is recessive so does not influence phenotype

Has positive effect because:
- Results in change in polypeptide that positively changes the properties (of the protein)
/ Results in change in polypeptide that positively changes a named protein
- May result in increased reproductive success / May result in increased survival (chances)

Question 5

Give two differences between mitosis and meiosis. (2)

Answer 5

• One division, two divisions in meiosis
• (Daughter) cells genetically identical, daughter cells genetically different in meiosis
• Two cells produced, (usually) four cells produced in meiosis
• Diploid to diploid/haploid to haploid, diploid to haploid in meiosis
• Separation of homologous chromosomes only in meiosis
• Crossing over only in meiosis
• Independent segregation only in meiosis

Question 5

Explain how the chromosome number is halved during meiosis. (2)

Answer 5

• Homologous chromosomes (pair)
• One of each (pair) goes to each (daughter) cell / to opposite poles

Question 6

Crossing over greatly increases genetic diversity in this species of moss. Describe the process of crossing over and explain how it increases genetic diversity. (4)

Answer 6

• Homologous pairs of chromosomes associate / form a bivalent
• Chiasma(ta) form
• (Equal) lengths of (non-sister) chromatids / alleles are exchanged
• Producing new combinations of alleles