Meiosis

Question 1

What are diploid cells?

Answer 1

• Contain two of each type of chromosome- one from father and one from mother
• Contain homologous chromosomes- same genes

Produced when a diploid cell divides by mitosis

Question 2

What are haploid cells?

Answer 2

Contain only one of each type of chromosome.

Produced when a diploid cell divides by meiosis OR when a haploid cell divides by mitosis

Question 3

What is the purpose of meiosis?

Answer 3

• Produces haploid gametes that contain a haploid number of chromosomes
• Has different combination of alleles- genetic variation

Question 4

Prophase 1

Answer 4

• Homogenous Chromosomes line up to from bivalent at chiasma
• Centriole pairs move to opposite poles of the cell
• Nucleoli and nuclear envelope splits
• Spindle forms

Question 5

Metaphase 1

Answer 5

• Bivalent lines up along the equator of the spindle
• Centromeres attach to the spindle fibres

Question 6

Anaphase 1

Answer 6

• Homologous chromosomes separate - spindle fibres shorten pulling centromeres to opposite poles of the cell

Question 7

Telophase 1
(Only sometimes occurs)

Answer 7

• Chromosomes begin to decondense
• nuclear envelope forms

Question 8

Prophase 1

Answer 8

• Chromosomes condense
• Nucleoli & nuclear envelope disappear
• New spindle forms at 90 degrees

Question 9

Metaphase 2

Answer 9

• Sister Chromatids line up along equator of the spindle
• Centromeres attach to spindle fibres

Question 10

Anaphase 2

Answer 10

• Centromeres divide
• Sister chromatids separate - spindles shorten pulling each chromatid towards the opposite pole of the cell

Question 11

Telophase 2
(only sometimes occur)

Answer 11

• Chromosomes decondense
• Nucleoli & nuclear envelopes form
• Cytoplasm divides- cytokinesis

Question 12

What are the two events in meiosis that introduce genetic variation?

Answer 12

Prophase 1: crossing over & recombination
- Crossing over involves chromatids breaking
- Swap parts to form new allele combinations

Metaphase 1: independent assortment of chromosomes
- Produces gametes with different combinations of chromosomes

Question 13

How does crossing over introduce genetic variation?

Answer 13

Homologous chromosomes condense and form bivalents, Chiasmata form when chromatids from each chromosome attach, Crossing over occurs at chiasmata, leading to chromatids breaking and detached parts swapping over and recombining

This process produces 4 chromatids with different allele combinations.

Question 14

In which stages do key meiosis events occur?

Answer 14

• Meiosis 1: Pairing of homologous chromosomes
• Meiosis 1: Chiasmata formation
• Meiosis 1: Independent assortment of chromosomes
• Prophase 1 and 2: Each chromosome consists of a pair of chromatids
• Meiosis 2: Chromatids separate

Key events occur at specific stages of meiosis