4.3 Gene mutation

Question 1

What is a mutation?

Answer 1

any change to the quantity or base sequence of the DNA of an organism

Question 2

What is a gene mutation?

Answer 2

Any change to one or more nucleotide base or a change in the sequenced of the bases, in DNA

Question 3

What are the 3 main ways the DNA sequence can change?

Answer 3

• addition of a base
• substitution of a base
• deletion of a base

Question 4

What are the causes of a mutation?

Answer 4

• can be spontaneous during DNA replication
• Some things increase the rate of mutations: UV radiation, ionising radiation, some chemicals and some viruses

Question 5

Why might a mutation not lead to a change in the amino acid sequence?

Answer 5

• genetic code is degenerate so mutation may end up coding for same amino acid as the original triplet
• mutation may occur in intron

Question 6

What is substitution mutation?

Answer 6

When a nucleotide in the DNA sequence is replaced by another. This is more likely to be a quiet mutation, meaning no changes occur in the amino acid sequence

Question 7

What is a deletion mutation?

Answer 7

When a nucleotide in the DNA sequence is lost. This is more likely to be harmful and significant, as it leads to a frame shift which means the entire amino acid sequence will be different

Question 8

What is a mutagenic agent?

Answer 8

Factors that increase the rate of a gene mutation. X-rays, UV light, gamma rays, certain chemicals

Question 9

What is a polyploidy chromosome mutation?

Answer 9

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

Question 10

What is chromosome non-disjunction?

Answer 10

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

Question 11

What is meiosis?

Answer 11

A form of cell division that produces 4 genetically different haploid cells known as gametes

Question 12

How does meiosis differ from mitosis?

Answer 12

-Meiosis produces 4 genetically different cells with half the number of chromosomes as the parent cell
- Mitosis produces 2 genetically identical cells with the same number of chromosomes as the parent cells

Question 13

What happens in meiosis 1?

Answer 13

• homologous chromosomes pair up and their chromatids wrap around each other
• Crossing over (exchange of sections of genetic material) occurs in chiasmata
• Cells divide into two. Homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy

Question 14

What happens during meiosis 2?

Answer 14

• the chromatids move apart
• each cell divides again, producing haploid cells

Question 15

Give 2 ways meiosis produces genetic variation.

Answer 15

• crossing over during meiosis 1
• independent assortment of homologous chromosomes and sister chromatids result in new combinations of alleles

Question 16

What is independent segregation?

Answer 16

• happens in meiosis 1 when each chromosome lines up alongside its homologous partner
• the chromosomes can line up in any order resulting in different possible combinations

Question 17

What is crossing over?

Answer 17

• the chromatids of each pair become twisted around one another
• during this twisting process tensions are created and portions of the chromatids break off
• these broken portions might then rejoin with the chromatids of its homologous partner
• Usually it is the equivalent portions of homologous chromosomes that are exchanged
• in this way new genetic combinations of maternal and paternal alleles are produced
• Chromatids cross over one another many times and so the process is known as crossing over. The broken portions of chromatid recombine with another chromatid, so this process is called recombination

Question 18

How can independent segregation be calculated?

Answer 18

2^n where n = the number of pairs of homologous chromosomes