4.3

Question 1

gene mutation

Answer 1

change in dna base sequence
can arise spontaneously during dna replication

Question 2

mutagenic agent

Answer 2

increase rate of gene mutation eg uv

Question 3

Mutation leading to non functional protiens

Answer 3

Change sequence of base triplets I’m dna so changes sequence codons in mRNA
Change AA seq in polypeptides
Change position of bonds
Changes tertiary structure
Enzyme active site changes shape So substrate can’t bind so ES can’t form

Question 4

Substitution effects

Answer 4

Base in dna replaced by another base
Change some triplet so changes one mRNA codon
So one AA in polypeptide changes
Tertiary structure may change if bond position changes
Or AA doesn’t change as degenerate or mutation in introns

Question 5

Deletion mutation

Answer 5

One base removed from DNA sequence
Change sequence of dna triplets from point of mutation
Changes sequence of mRNA codons after point of mutation
So AA seq in primary structure of polypeptide changes
Bond position changes so tertiary structure and shape of protein changes

Question 6

Homologous chromosome features

Answer 6

Same length and same genes but different alleles

Question 7

Diploid

Answer 7

2 complete sets of chromosomes 2N

Question 8

Haploid

Answer 8

Single set of unpaired chromosomes represented as n

Question 9

Cell division by meiosis

Answer 9

Meiosis 1 separates homologous chromosome chromosomes sp chromosomes arrange into homologous pairs
Crossing over and independent segregation
Meiosis 2 separates chromatids

Question 10

How does crossing over create genetic variation

Answer 10

Homologous pairs of chromosomes form bivalent
Chiasmata form
Alelles exchanged between chromosomes
Create new combo of maternal paternal alleles on chromosome

Question 11

Independent segregation and genetic variation

Answer 11

Homologous pairs randomly align at equator so random which chromosome from each pair goes to daughter cell
Creates dif combos of maternal and paternal alleles on chromosomes

Question 12

What else causes genetic variation

Answer 12

Random fertilisation

Question 13

Mitosis vs meiosis

Answer 13

Mitosis 2 daughter cells but meiosis 4 as 2 divisions
Mitosis genetically identical but meiosis genetically varied as crossing over and independent segregation
Mitosis maintains chromosome number but meiosis halves chromosomes number

Question 14

Importance of meiosis

Answer 14

2 division create haploid gametes halving the number of chromosomes
So diploid number is restored at fertilisation so chromosome number maintained between generations
Independent segregation and crossing over creates genetic variation

Question 15

How can you recognise where meiosis and mitosis occur in a life cycle?

Answer 15

Mitosis occurs between stages where chromosome number is maintained
Meiosis occurs between stages where chromosome number halves

Question 16

Describe how mutations in the number of chromosomes arise

Answer 16

● Spontaneously by chromosome non-disjunction during meiosis
● Homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate during meiosis
● So some gametes have an extra copy (n+1) of a particular chromosome and others have none (n-1)