4.3 - Genetic diversity can arise as a result of mutation or during meiosis

What is a mutation?

An alteration to the DNA base sequence.

Often arise spontaneously during DNA

replication.

Why might a mutation not lead to

change in the amino acid sequence?

● Genetic code is degenerate so

mutation may end up coding for same

amino acid as the original triplet.

● Mutation may occur in intron.

What is a substitution mutation?

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.

What is a deletion mutation?

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.

What is a mutagenic agent? Give

examples of this.

Factors that increase the rate of gene

mutation. X-rays, UV light, gamma rays,

certain chemicals e.g. in alcohol and

tobacco.

What is a polyploidy chromosome

mutation?

Where an individual has three or more

sets of chromosomes instead of two.

What is chromosome non-disjunction?

When chromosomes fail to separate

correctly in meiosis, resulting in gametes

with one more or less chromosome than

normal.

What is meiosis?

A form of cell division that produces four

genetically different haploid cells (cells

with half the number of chromosomes

found in the parent cell) known as

gametes.

How does meiosis differ from mitosis?

● 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.

What happens during meiosis Ⅰ?

1. Homologous chromosomes pair to form bivalents.

2. Crossing over (exchange of sections of genetic

material) occurs at chiasmata.

3. Cell divides into two. Homologous chromosomes

separate randomly. Each cell contains either

maternal or paternal copy.

What happens during meiosis Ⅱ?

1. Independent segregation of sister

chromatids.

2. Each cell divides again, producing 4

haploid cells.

Draw diagrams to show cells after each

stage of meiosis.

In which two ways does meiosis produce

genetic variation?

1. Crossing over during meiosis Ⅰ

2. Independent assortment (random

segregation) of homologous

chromosomes & sister chromatids

Result in new combinations of alleles.