Unit 4- 3.4.3 Genetic diversity can arise as a result of mutation or during meiosis

Question 1

Define the term mutagenic agent.

Answer 1

A factor that increases the rate of mutations

Question 2

Explain why a mutation involving the deletion of a base may have a greater effect than one involving substitution of one base for another. (3 marks)

Answer 2

1. deletion causes frame shift;
2. changes sequence of amino acids (from this point);
3. substitution alters one codon / triplet / one amino acid altered;
4. code degenerate / same amino acid coded for;

Question 3

Explain how a change in DNA lead to a change in the function of an enzyme. (4 marks)

Answer 3

1. Change in mRNA;
2. Change in primary structure/sequence of amino acids
3. H/ ionic bonds form in different places
4. Secondary structure is altered
5. Changes tertiary structure of active site.

Question 4

Explain how crossing over can contribute to genetic variation. (3 marks)

Answer 4

1. sections of chromatids exchanged;
2. sections have different alleles;
3. new combinations of (linked) alleles;

Question 5

Describe what happens in meiosis 1.

Answer 5

Separate homologous pairs

Question 6

Describe what happens in meiosis 2.

Answer 6

Separate sister chromatids

Question 7

A normal animal cell has 20 chromosomes and therefore 20 units of DNA.
How many chromosomes would there be in a sperm cell?

Answer 7

10

Question 8

A normal animal cell has 8 pairs of chromosomes. How many different types of gametes could be produced from this cell as a result of different combinations of maternal and paternal chromosomes

Answer 8

256 (2 to the power 8)

Question 9

Explain the role of independent segregation in meiosis. (2 marks)

Answer 9

1. (To provide) genetic variation;
2. (Allows) different combinations of maternal and paternal chromosomes / alleles;

Question 10

Name two ways in which meiosis produces genetic variation.

Answer 10

1. Crossing over
2. Independant Segregation of homologous chromosomes.

Question 11

Patau syndrome is a condition caused by a mutation affecting chromosome number. Cells have an extra chromosome 13.

Describe how the change in chromosome number in Patau syndrome was produced. (2 marks)

Answer 11

1. In meiosis;
2. Homologous chromosomes / sister chromatids do not separate / non-disjunction