genetic diversity as a result of mutation or during meiosis 3.4.3

Question 1

what is a gene point mutation

Answer 1

a change in one or more nucleotide bases
or a change in the sequence of bases
can be caused by mutagens or errors during DNA replication

Question 2

what is a chromosome mutation

Answer 2

a change in the number or structure of the chromosomes
caused by error during cell division

Question 3

what are the three causes of point mutation

Answer 3

base substitution
base deletion
base insertion

Question 4

what is a silent mutation

Answer 4

does not alter amino acid sequence even though nucleotide sequence has changed
(because of the degenerate code)

Question 5

what is a missense mutation

Answer 5

does not alter amino acid sequence

Question 6

what is a nonsense mutation

Answer 6

involves a change from a normal codon to a termination codon
causes synthesis of polypeptide to be terminated

Question 7

2 reasons why mutation may not change amino acid sequence

Answer 7

• degenerate code - different triplet may code for same amino acid
• mutation may occur in an intron

Question 8

what is a substitution mutation

Answer 8

nucleotide in DNA sequence is replaced by another

Question 9

what is a deletion mutation

Answer 9

nucleotide in DNA sequence is lost
leads to a frame shift
entire amino acid sequence will be different

Question 10

what is a mutagenic agent

Answer 10

factors that increase the rate of gene mutation

Question 11

examples of mutagenic agents

Answer 11

UV light, X rays, gamma rays, tobacco, alcohol

Question 12

what is a polyploidy chromosome mutation

Answer 12

when an individual has three or more sets of chromosomes instead of two

Question 13

what is chromosome non-disjunction

Answer 13

chromosomes fail to separate correctly in meiosis
results in gametes with one more or less chromosome than normal

Question 14

what does meiosis produce

Answer 14

4 genetically different haploid cells known as gametes

Question 15

what happens during meiosis 1

Answer 15

1 homologous chromosomes pair to form bivalents
2 crossing over occurs at chiasmata
3 cell divides in two
homologous chromosomes separate randomly

Question 16

what happens during meiosis 2

Answer 16

1 independent segregation of sister chromatids
2 each cell divides again (same process as mitosis) producing 4 haploid daughter cells

Question 17

in which 2 ways does meiosis produce genetic variation

Answer 17

1 crossing over during meiosis one
2 independent segregation of homologous chromosomes and sister chromatids
results in a new combination of alleles

Question 18

Describe the process of crossing over and explain how it increases genetic diversity. (4 marks)

Answer 18

Homologous pairs of chromosomes form a bivalent
Chiasmata form
lengths of chromatids are exchanged
producing a new combination of alleles

Question 19

Apart from mutation, explain one other way genetic variation within a species is increased. (2 marks)

Answer 19

random fertilisation
produces new allele combinations

Question 20

Define ‘gene mutation’ and explain how a gene mutation can have:
- no effect on an individual
- a positive effect on an individual
(4 marks)

Answer 20

change in the nucleotide sequence
results in formation of new allele
no effect - genetic code is degenerate
positive effect - results in change in polypeptide that positively changes it’s properties

Question 21

differences between mitosis and meiosis (4)

Answer 21

1 One division in mitosis two divisions in meiosis
2 two cells produced in mitosis, four in meiosis
3 crossing over only in meiosis
4 independent segregation only in meiosis