Meiosis

Question 1

What are the features of homologous chromosomes?

Answer 1

• Same size
• Same position of centromeres
• Identical sequence of gene loci
• Pair with each other during prophase I of meiosis
• Same genes, but not same alleles (alternative forms of genes)
• Combination of genes the same, combination of alleles not the same

Question 2

What is the significance of meiosis?

Answer 2

1. Prevent doubling of chromosomes in sexual reproduction
2. Generates genetic variation by:
   * Chiasmata formation and crossing over between non-sister chromatids of homologous chromosomes
   * Independent assortment of homologous chromosomes
   * Fertilisation

Question 3

What happens during interphase?

Answer 3

• DNA replicates during S phase of interphase
• Centrioles replicate before meiosis I

Question 4

What happens during prophase I?

Answer 4

• Chromatin condense to chromosomes
• Nuclear envelope distintegrates
• Centrioles move to opposite poles of the cell
• Spindle fibres form
• Homologous chromosomes pair up and crossing over occurs

Crossing over is the breakage and rejoining between two non sister chromatids of the pair of homologous chromosomes at the chiasmata.
* Involves the exchange of genetic material between homologous chromosomes, resulting in formation of new combinations of alleles.

Question 5

What happens during metaphase I?

Answer 5

• Homologous chromosomes arranged along equator of metaphase plate
• Spindle fibres attached to centromeres of chromosomes via the kinetochore
• Independent assortment

Question 6

What happens during anaphase I?

Question 7

What happens during telophase I?

Question 8

What happens during prophase II?

Question 9

What happens during metaphase II?

Question 10

What happens during anaphase II?

Question 11

What happens during telophase II?

Question 12

State the types of chromosome aberration.

Answer 12

• Change in structure of chromosomes (structural aberration)
• Change in number of chromosomes (numerical aberration)

Question 13

List the types of structural chromosome aberration.

Answer 13

• Deletion
• Inversion
• Translocation
• Duplication

Question 14

List the types of numerical chromosome aberration.

Answer 14

• Aneuploidy
• Polyploidy

Question 15

What is non-disjunction?

Answer 15

Non-disjunction refers to:
* the failure of sister chromatids to separate during anaphase (mitosis) or
* the failure of homologous chromosomes to separate during anaphase I or
* the failure of sister chromatids to separate during anaphase II of meiosis