4.3 Genetic Diversity Due To Mutation Or Meiosis

Question 1

Describe substitution - non sense mutation

Answer 1

A base mutates into a different base, producing a premature stop codon. Results in premature end to polypeptide synthesis - non functional polypeptide usually is the result

Question 2

Describe substitution - mis sense mutation

Answer 2

Change in base sequence produces a different amino acid, which results in a change to the tertiary structure
The effect of this mutation is determined by the role of the amino acid in the polypeptide
e.g. It may be involved in the bond formation of an active site which would cause the enzyme to no longer be complimentary

Question 3

Describe deletion - frameshift

Answer 3

A nucleotide is lost from DNA sequence
Changes reading frame of codons due to bases being read in triplets so subsequent bases are shifts forward as bases are non-overlapping
Amino acid sequence results in a non functional protein usually

Question 4

Describe chromosome mutation

Define non-disjunction

Answer 4

Occurs if homologous pairs do not separate during gamete formation in meiosis, resulting in a gamete having more or fewer chromosomes than normal e.g Down’s syndrome

Non disjunction - changes in the number of individual chromosomes

Question 5

What is diploid number

What is the diploid number in humans?

Answer 5

Each cells contains two of each chromosome

46 in humans

Question 6

What is haploid number?

What is the haploid number in humans?

Answer 6

Each gametes contains one copy of a chromosome

23

Question 7

Describe meiosis - 1st division

4 steps

Answer 7

1. DNA replication - sister chromosomes joined by a centromere
2. Synapsis occurs - The chromosomes arrange themselves in a bivalent along the equation
3. Independent segregation occurs - the bivalents line up in any orientation along the equator so that paternal and maternal versions of different chromosomes are mixed in the final gametes
4. Crossing over occurs - while chromosomes are joined in a bivalent, parts of each chromosome swap with corresponding parts. The point of cross over is called a chiasma. Crossing over does not always occur

Question 8

Describe meiosis - second division

Answer 8

1. Sister chromatides divide
2. 4 haploid cells are produced which are genetically different and each cell has a different chromatid - different set of alleles. This increases genetic variation of offspring

Question 9

What does meiosis do

Answer 9

Restores diploid number so diploid number is maintained every generation
Increases genetic variation in offspring

Question 10

Formula for number of combinations of chromosomes in gametes

Formula for the number of random pairings of male and female gametes

Answer 10

2^n

(2^n)^2

Question 11

Describe substitution - silent mutation

Answer 11

A base is substituted with a different base without affecting the amino acid produced. The codon still codes for the same amino acid because the code is Degenerate - 64 codons, 20 amino acids - some codons code for the same amino acid