Section 4 exam questions

Question 1

Define mutagenic agent

Answer 1

A factor that increases the rate of mutation`

Question 2

Name the type of mutation that changed the number of chromosomes in S.
townsendii to produce S. anglica. Explain your answer (Number of chromosomes doubles)

Answer 2

Non disjunction
In meiosis
Chromosomes do not seperate/all chromosomes stay in one cell/ chromosomes don’t form homologous pairs

Question 3

Genetic variation within a species is increased during meiosis by crossing
over and the independent segregation of homologous chromosomes.
Apart from mutation, explain one other way genetic variation within a
species is increased

Answer 3

Random fusion of gametes/fertilisation of gametes

Produces new combinations of alleles

Question 4

A trout body cell contains 80 chromosomes.
Farmed female trout are treated so that they produce diploid egg cells.
The offspring produced from farmed trout are sterile. Suggest and explain
why

Answer 4

Too many/extra set/3 copies of chromosomes
Homologous chromosomes don’t pair/don’t separate evenly
No meiosis

Question 5

Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual

Answer 5

A change in the base sequence of DNA
Results in formation of a new allele

Genetic code is degenerate- amino acid sequence may not change
Mutation is an intron so amino acid sequence may not change
Amino acid sequence changes but has no effect on tertiary structure of protein
Allele is recessive so has no influence on phenotype

Results in change in polypeptide that positively changes the
properties (of the protein)
OR
Results in change in polypeptide that positively changes a named
protein
Results in increased survival chances