2.1.6 Cell Division – Meiosis

Question 1

What are gametes?

Answer 1

• They are sex cells
• In animals, they are sperm cells in males and egg cells (or ova) in females.
• In plants, they are pollen in males and ovules in females

Question 2

What are homologous chromosomes?

Answer 2

Matching chromosomes that contain the same genes in the same loci. Homologous chromosomes form pairs. They may have different alleles for some of these genes.

Question 3

What is meiosis?

Answer 3

The type of nuclear division that results in the formation of cells that contain half the number of chromosomes to the parent cell and are genetically not identical to the parent cell.

Question 4

What does the term haploid mean?

Answer 4

Half the full number of chromosomes e.g. 23 in humans.

Question 5

What does the term diploid mean?

Answer 5

The full number of chromosomes e.g. 46 in humans.

Question 6

Why is meiosis important?

Answer 6

Meiosis halves the chromosome number producing haploid gametes. This means that the chromosome number can be maintained after fertilisation.

Question 7

How many divisions take place during meiosis?

Answer 7

Two

Question 8

List all the ways meiosis produces genetic variation.

Answer 8

• The crossing over in prophase 1 shuffles the alleles.
• Independent assortment of the chromosomes in anaphase 1 and anaphase 2 randomly distributes the paternal and maternal chromosomes.
• Random fusion with gametes derived from another organism of the same species.

Question 9

What events take place during prophase 1 of meiosis?

Answer 9

• Chromosomes condense
• Nuclear envelope disintegrates
• Spindle fibres begin to form
• Homologous chromosomes pair up forming bivalents
• Crossing over occurs.

Question 10

What is crossing over in prophase 1?

Answer 10

Homologous pair of chromosomes come together and pair up. The chromatids twist around each other, forming chiasma and sections of chromatids swap over. The chromatids still contain the same gene but now have a different combination of alleles.

Question 11

What events take place in metaphase 1 of meiosis?

Answer 11

• The chromosomes line up along the equator region as spindles attach to the centromere of the chromosomes.
• Chromosomes are independently assorted as each of the chromosomes in a pair randomly face opposite poles.

Question 11

What events take place in prophase 2 of meiosis?

Answer 11

• Chromosomes re-condense
• Nuclear envelop breaks down again
• Spindle fibres reform

Question 12

What events take place in anaphase 1 of meiosis?

Answer 12

• Independent segregation - homologous chromosomes are pulled by the spindle fibres to the poles.
• The chromatids are not pulled apart.

Question 13

What events take place in telophase 1 of meiosis?

Answer 13

• Nuclear envelopes reform
• Chromosomes uncoil
• The cells undergo cytokinesis
• These cells are now haploid cells

Question 14

What events take place in anaphase 2 of meiosis?

Answer 14

• Chromosomes are a lined on the equator by the spindle fibres.
• Independent assortment of sister chromatids occurs.

Question 15

What events take place in metaphase 2 of meiosis?

Answer 15

• Centromeres break and sister chromatids are split apart by the spindle fibres.
• Chromatids move to the poles of the cells.

Question 16

What events take place in telophase 2 of meiosis?

Answer 16

• Chromatids uncoil
• Nuclear envelopes reform
• The cell undergoes cytokinesis
• 4 haploid daughter cells are produced