3.4.3 Genetic diversity can arise as a result of mutation or meiosis

Question 1

Meiosis – Causes of Variation (6)

Answer 1

1. Homologous chromosomes pair up;
2. Chiasmata formed
3. Independent segregation;
4. Maternal and paternal chromosomes are re-shuffled in any combination;
5. Crossing over leads to exchange of parts of (non-sister) chromatids/alleles between homologous chromosomes;
6. (Both) create new combinations of alleles

Question 2

Meiosis – Process of Crossing Over (4)

Answer 2

1. Homologous pairs of chromosomes associate / form a bivalent;
2. Chiasmata(ta) form;
3. (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
4. Producing new combinations of alleles;

Question 3

Describe how the process of meiosis results in haploid cells (4)

Answer 3

1. DNA replication (in interphase) creates two identical chromatids;
2. (meiosis has) two nuclear divisions;
3. (first division) Homologous pairs separated
4. (second division) sister chromatids separated

Question 4

Define mutation

Answer 4

A change in the base sequence of DNA, results in a new allele

Question 5

What is meant by the degenerate code?

Answer 5

More than one codon codes for a single amino acid;

Question 6

Mutation - How does mutation cause change in enzyme function (3)

Answer 6

1. Change in amino acid / (sequence of) amino acids / primary structure;
2. Change in hydrogen / ionic / disulphide bonds alters tertiary structure / active site (of enzyme);
3. Substrate not complementary / cannot bind (to enzyme / active site) / no enzyme- substrate complexes form;

Question 7

Mutation - How does mutation cause change in protein (receptor) structure? (4)

Answer 7

1. Change in DNA base (sequence);
2. Change in amino acid (sequence)/primary structure;
3. Alters (position of) hydrogen/ionic/disulfide bonds;
4. Change in tertiary structure (of receptor);

Question 8

Mutation – Mutation leading to evolutionary
changes/phylogenetic relationships

Answer 8

1. Mutations change base / nucleotide (sequence);
2. (Causing) change in amino acid sequence;
3. Mutations build up over time;
4. Few(er) mutations / differences (in amino acid / base / nucleotide sequence / primary structure) in closely related
   species;
5. Closely related species have recent common ancestor

Question 9

Define the term mutagenic agent.

Answer 9

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

Question 10

Name ways which increase genetic variation in a
population

Answer 10

1. Mutation;
2. Meiosis – crossing over and independent segregation
3. Random fertilisation/random fusion of gametes

Question 11

Define how a mutation can have a positive effect on an individual and no effect on a individual

Answer 11

No effect because:
1. Genetic code is degenerate/codon codes for the same amino acid
2. Mutation is in an intron
3. Creates a recessive allele which does not affect phenotype
Positive effect because:
4. (new allele) increases chance of survival