BY5.1 - Meiosis

Question 0

What does homologous mean?

Answer 0

Pairs of chromosomes that are the same length

Question 1

What is Humans diploid number?

Answer 1

46 (23 pairs)

Question 2

Outline the changes that occur in Interphase I

Answer 2

1) Chromosomes are in chromatin form (not visible)
2) DNA undergoes semi-conservative replication
- 4 copies of each chromosome are now present (2 maternal, 2 paternal)

Question 3

What changes happen in Prophase I?

Answer 3

1) DNA condenses and chromosomes become visible

2) Nuclear membrane breaks down

3) One chromosome has become 2 sister chromatids held at the centromere
4) Homologous chromatids pair up forming Bivalents (4 chromatids - 2 chromosomes joined)
5) Chromosomes entwine forming Chiasmata

6) Crossing over - parts of maternal and paternal DNA break and interchange

Question 4

What changes happen in Metaphase I?

Answer 4

1) Centrioles move to the poles
2) Spindle fibres form
3) Bivalents move to equator
4) Chromatids attach to spindle at centromeres
5) Random assortment

Question 5

What happens at Anaphase I?

Answer 5

1) Homologous pairs of chromatids separate
2) Spindle fibres contract - pull chromatids to opposite poles

Question 6

​What changes happen in Telophase I?

Answer 6

1) Spindle fibres break down

2) Cell enters prophase II

Question 7

What happens at Prophase/ Metaphase II

Answer 7

1) New spindle fibres form at right angles to the old
2) Each pair of sister chromatids move to equator
3) Chromatids attach to spindle fibres at centromere
4) Haploid cell - no homologous pairs

Question 8

What happens at Anaphase II?

Answer 8

1) Centromeres divide
2) Spindle fibres contract and pull chromatids to poles

Question 9

What happens in telophase II

Answer 9

1) Chromosomes lengthen - become chromatin
2) Spindle fibre breaks down
3) Nuclear membrane reforms
4) Cytokinesis - 4 haploid cells - genetic variation