3.4.3

Question 1

What is a gene mutation?

Answer 1

A change in base sequence in DNA

Question 2

Name 2 causes of gene mutations

Answer 2

Spontaneous error during DNA replication
Mutagenic agents

Question 3

What are mutagenic agents and what do they do?

Answer 3

Factors that increase the rate of gene mutation

Question 4

Describe the 3 types of gene mutation

Answer 4

Substitution- when one or more bases are changed in the DNA sequence
Deletion- when one or more bases are removed from the DNA sequence
Insertion- when one or more bases are added to the DNA sequence

Question 5

Why are some mutations harmless?

Answer 5

Occur in introns
Due to degenerate nature of genetic code not all substitutions cause a change in encoded amino acids

Question 6

What is a frame shift?

Answer 6

When a base is inserted, removed or duplicated
Alters the number of bases in the DNA sequence
Means all the subsequent triplet codes are altered

Question 7

Where does meiosis occur in humans?

Answer 7

Ovaries and testes

Question 8

What does meiosis produce?

Answer 8

Genetically different daughter cells
Gametes with the haploid (half) number of chromosomes

Question 9

How many divisions are in meiosis?

Answer 9

2
First separates homologous chromosomes
Second separates chromatids

Question 10

Why do gametes have a haploid number of chromosomes?

Answer 10

Fuse together in fertilisation to restore the diploid number

Question 11

Describe how meiosis leads to genetic variation

Answer 11

Independent segregation of homologous chromosomes- paternal and maternal reshuffled in any combination
Homologous chromosomes cross over at the chiasma creating new combinations of alleles by exchanging

Question 12

Describe crossing over and how it leads to genetic diversity

Answer 12

Homologous chromosomes associate with each other
Cross over at chiasma
Exchange lengths of chromatids
Produces new combinations of alleles