3.4.3 Meiosis and Mutations

Question 1

What is a gene mutation?

Answer 1

Change in DNA base sequence of chromosome

Gene mutations can happen spontaneously during DNA replication.

Question 2

What can increase the rate of mutation?

Answer 2

Mutagenic agents such as ionising radiation and chemicals

These agents can induce changes in the DNA sequence.

Question 3

What are the three types of base changes in gene mutations?

Answer 3

• Substituted
• Deleted
• Added

Substitution may have no effect, change an amino acid, or introduce a stop codon.

Question 4

What is non-disjunction?

Answer 4

Chromosomes do not separate during anaphase in meiosis

Non-disjunction can lead to conditions like Down’s syndrome.

Question 5

What is the outcome of meiosis?

Answer 5

Produces daughter cells which are genetically different from each other

Meiosis involves two nuclear divisions.

Question 6

How many haploid daughter cells are produced from a single diploid parent cell during meiosis?

Answer 6

4 haploid daughter cells

This occurs after two rounds of division.

Question 7

What is the state of chromosomes before meiosis begins?

Answer 7

Chromosomes consist of two identical (sister) chromatids, joined at a centromere

This occurs after DNA replication.

Question 8

What happens during Prophase I of meiosis?

Answer 8

• Chromosomes condense and become visible
• Homologous chromosomes attach at chiasmata
• Spindle fibres form

Bivalents are formed during this stage.

Question 9

What occurs during Metaphase I of meiosis?

Answer 9

Homologous pairs of chromosomes attach to spindle fibres at the equator of the cell

This positioning is crucial for the separation of chromosomes.

Question 10

What happens during Anaphase I of meiosis?

Answer 10

• Homologous pairs separate
• Individual chromosomes are pulled to the poles of the cell

Spindle fibres contract during this process.

Question 11

What occurs during Telophase I of meiosis?

Answer 11

• Chromosomes uncoil
• Spindle fibres break down
• Haploid nuclei form

This marks the end of the first meiotic division.

Question 12

What happens during Prophase II of meiosis?

Answer 12

• Chromosomes condense and become visible
• Spindle fibres form

This stage prepares for the second meiotic division.

Question 13

What occurs during Metaphase II of meiosis?

Answer 13

Chromosomes line up at the equator of the cell and attach to spindle fibres by the centromeres

This alignment is essential for proper chromosome separation.

Question 14

What happens during Anaphase II of meiosis?

Answer 14

• Chromosomes separate
• Chromatids are pulled to the poles of the cell

Spindle fibres contract, pulling chromatids by the centromeres.

Question 15

What occurs during Telophase II of meiosis?

Answer 15

• Chromosomes uncoil
• Spindle fibres break down

This concludes the second meiotic division.

Question 16

What is independent segregation of homologous chromosomes?

Answer 16

Maternal and paternal chromosomes can be positioned either side of the equator of the cell during metaphase I

This results in different combinations of chromosomes in daughter cells.

Question 17

What is crossing over?

Answer 17

Sections of non-sister chromatids can be exchanged when the chiasmata break

This occurs during prophase and metaphase I, resulting in new combinations of alleles.

Question 18

What is random fertilisation?

Answer 18

Each individual organism produces genetically varied gametes, leading to an equal probability of any female gamete fusing with any male gamete

This process increases genetic variation within a species.