4.3 Genetic Diversity Can Arise As A Result of Mutation or During Meiosis

Question 1

What is a mutation?

Answer 1

• An alteration to the DNA base sequence
• Often arises spontaneously during DNA replication

Question 2

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

Answer 2

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

Question 3

What is a substitution mutation?

Answer 3

• When a nucleotide in the DNA sequence is replaced by another
• This is more likely to be a quiet mutation, meaning no change occurs in the amino acid sequence

Question 4

What is a deletion mutation?

Answer 4

• When is 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 5

What is a mutagenic agent?

Answer 5

Factors that increase the rate of gene mutation

Question 6

Examples of a mutagenic agent

Answer 6

• X-rays
• UV light
• Gamma rays
• Chemicals in alcohol and tobacco

Question 7

What is a polyploidy chromosome mutation?

Answer 7

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

Question 8

What is a chromosome non-disjunction?

Answer 8

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

Question 9

What is meiosis?

Answer 9

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

Question 10

How does meiosis differ from mitosis?

Answer 10

• Meiosis produces four genetically different cells with half the number of chromosomes as the parent cells
• Mitosis produces two genetically identical cells with the same number of chromosomes as the parent cells

Question 11

What happens during meiosis 1?

Answer 11

1. Homologous chromosomes pair to form bivalents
2. Crossing over occurs at the chiasmata
3. Cell divides in two, homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy

Question 12

What happens during meiosis 2?

Answer 12

1. Independent segregation of sister chromatids
2. Each cell divides again, producing 4 haploid cells

Question 13

Draw diagrams to show cell contents after each stage of meiosis

Answer 13

Question 14

Give two ways meiosis produces genetic variation

Answer 14

1. Crossing over during meiosis 1
2. Independent assortment and random segregation of homologous chromosomes and sister chromatids

Question 15

What does crossing over and independent segregation result in?

Answer 15

New combinations of alleles