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

Question 1

What is a gene mutation?

Answer 1

A gene mutation is a change in the base sequence of DNA.

Question 2

When do gene mutations arise?

Answer 2

Gene mutations arise spontaneously during DNA replication.

Question 3

Name two types of gene mutations.

Answer 3

Base deletion and base substitution.

Question 4

Why do not all base substitutions cause a change in the amino acid sequence?

Answer 4

Because of the degenerate nature of the genetic code where more than one codon codes for the same amino acid.

Question 5

What can increase the rate of gene mutation?

Answer 5

Mutagenic agents increase the rate of gene mutation.

Question 6

How can mutations in the number of chromosomes arise?

Answer 6

Mutations in chromosome number arise by chromosome non-disjunction during meiosis.

Question 7

What does meiosis produce?

Answer 7

Meiosis produces daughter cells that are genetically different from each other.

Question 8

How many divisions occur in meiosis and what is produced?

Answer 8

Two nuclear divisions produce four haploid daughter cells from a single diploid parent cell.

Question 9

How does independent segregation create genetic variation?

Answer 9

Independent segregation of homologous chromosomes produces genetically different daughter cells.

Question 10

How does crossing over create further genetic variation?

Answer 10

Crossing over between homologous chromosomes results in further genetic variation among daughter cells.

Question 11

Explain the different outcome of mitosis and meiosis.

Answer 11

Mitosis produces two genetically identical diploid cells meiosis produces four genetically different haploid cells.

Question 12

How does random fertilisation increase genetic variation?

Answer 12

Random fertilisation of haploid gametes produces new combinations of alleles increasing genetic variation within a species.

Question 13

Meiosis – Causes of Variation (6)

Answer 13

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 14

Meiosis – Process of Crossing Over (4)

Answer 14

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 15

Describe how the process of meiosis results in haploid cells.

Answer 15

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 16

Define mutation

Answer 16

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

Question 17

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

Answer 17

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 18

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

Answer 18

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 19

Mutation – Mutation leading to evolutionary changes/phylogenetic relationships

Answer 19

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 20

Define the term mutagenic agent.

Answer 20

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

Question 21

Name ways which increase genetic variation in a population

Answer 21

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

Question 22

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

Answer 22

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