Meiosis and mutations

Question 1

Compare and contrast meiosis and mitosis

Answer 1

Comparison=
- In both, DNA is replicated at the start
- In both the daughter cells produced can be haploid

Contrast=
- In meiosis there are 2 divisions but in mitosis there’s only 1 division
- In meiosis 4 daughter cells are produced whereas in mitosis only 2 are produced
- In meiosis, crossing over and independent segregation occur whereas they don’t in mitosis
- The daughter cells are genetically identical in mitosis whereas in meiosis they are genetically different
- In meiosis homologous chromosomes separate whereas they don’t in mitosis

Question 2

State another way genetic variation increases (not crossing over or Independent seg.)

Answer 2

Random fertilisation of gametes happens after meiosis. Each gamete is fertilised with different alleles

Question 3

Describe what happens during Independent segregation and explain how it creates genetic variation

Answer 3

When homologus pairs line up at the equator of the cell maternal and paternal chromosomes can form different combinations

Question 4

Describe what happens during crossing over and explain how it increases genetic variation

Answer 4

• Homologus pairs of chromosomes associate to form a bivalent
• Chiasmata form
• Equal lengths of non- sister chromatids and alleles are exchanged
• This produces new combinations of alleles in the gametes

Question 5

What is meant by haploid?

Answer 5

A haploid cell is a cell containing one of each type of chromosome e.g. a gamete
It is represented by n

Question 6

What is meant by diploid?

Answer 6

A diploid cell is a cell containing 2 of each type of chromosome e.g. a normal body cell
It is represented by 2n

Question 7

What is chromosome non-disjuction?

Answer 7

A spontaneous mutation that can occur in meiosis is called chromosome non- disjunction

Homologus chromosomes (1st division) or sister chromatids (2nd division) aren’t separate forming gametes with 1 more/ 1 less chromosome.
It can lead to genetic diseases like Down syndrome

Question 8

What are homologus chromosomes?

Answer 8

Homologus chromosomes are a pair of chromosomes which have the same genes at the same gene loci but many have different alleles

Question 9

What is a mutation and how does it arise?

Answer 9

A gene mutation is a change in the DNA base sequence of a chromosome which leads to the formation of a new allele.

Question 10

A mutation can lead to the production of a non- functional enzyme. Explain how (7)

Answer 10

• mutation is a change in the DNA base sequence
• changes the amino acid sequence of a polypeptide
• changes the position of the hydrogen, ionic and disulphide bonds between amino acids
• changes the tertiary structure
• active site changes shape
• so active site isn’t complementary to the substrate
• no enzyme- substrate complexes form

Question 11

Describe how a mutation can create a non- functional protein

Answer 11

• change in the DNA base sequence
• changes the amino acid sequences of the polypeptide
• changes the position of the hydrogen, ionic and disulphide bonds between amino acids
• changes the tertiary structure

Question 12

Name some possible mutagenic agents

Answer 12

• High energy environments- X-rays, UV radiation
• Chemicals- benzene, asbestos

Question 13

What is a deletion mutation?

Answer 13

when one base is removed from the DNA

Question 14

Describe and explain the possible effect of a substitution mutation on a protein

Answer 14

Substitution mutations don’t always result in a change to the amino acid sequence. This is because the genetic code is degenerate so some amino acids are coded for by more than 1 triplet

Question 15

What is a substitution mutation?

Answer 15

when one base is swapped for another base

Question 16

Describe and explain the effect of the deletion mutation on a protein

Answer 16

Deletion mutations always result in a change to the amino acid sequence. This is because deletion mutations result in a frame shift so that all triplet codes and amino acids from the point of mutation change.