Lecture 3 - sexual cell cycle

Question 1

What type of cell division creates diversity?

Answer 1

Sexual cell cycle

Question 2

What type of cells are created via meiosis?

Answer 2

4 haploid

Question 3

How many successive nuclear divisions are there in meiosis?

Answer 3

2 - both sets of sister chromatids go to separate poles. These are then separated into individual chromosomes - leading to haploid cells

Question 4

What are tetrad cells?

Answer 4

4 haploid products of meiosis

Question 5

What is the process of going from a diploid cell to a haploid cell called?

Answer 5

meiosis

Question 6

What is the process of going from a haploid cell to a diploid cell called?

Answer 6

nuclear fission

Question 7

Describe the nuclear cycle in Saccharomyces cerevisiae?

Answer 7

Haploid throughout most of life - 2 mating types (a & alpha) - both combine to give a transient diploid stage, before meiosis occurs, giving 4 haploid products

Question 8

Describe what is present at the end of meiosis 1?

Answer 8

there are 2 nuclei, each containing both sister chromatids of 1chromosome - from each pair of homologues - different from the cell

Question 9

What is the name given to each replicated chromosome - 2 sister chromatids with a single centromere?

Answer 9

Dyad

Question 10

What is the name given to 2 dyads joined together?

Answer 10

Bivalent

Question 11

What occurs during anaphase 1?

Answer 11

Dyads move to different poles - centromere stays intact

Question 12

What are the 5 stages of prophase in Meiosis 1?

Answer 12

1. leptotene
2. zygotene
3. pachytene (crossing over)
4. diplotene
5. diakinesis

Question 13

What occurs during leptotene?

Answer 13

replicated chromosomes start to contract

Question 13

What occurs during zygotene?

Answer 13

chromosomes line up in homologous pairs (synapsis), held together by a protein complex called synaptonemal complex

Question 13

What occurs during anaphase 2 in meiosis 2?

Answer 13

• centromere splits
• chiasmata break down
• chromatids move to opposite poles

Question 13

What occurs during pachytene (crossing over)?

Answer 13

genetic exchange between non-sister chromatids

Question 13

What occurs during diplotene?

Answer 13

chromosomes separate a bit but sites of crossing over are still visible

Question 13

what occurs during diakinesis?

Answer 13

chromosomes contract even further

Question 13

What is present at the end of Meiosis 2 (like haploid mitosis)?

Answer 13

4 nuclei:
- 2 contain 1 copy of the first homologous
- 2 contain one copy of the second

Question 13

What occurs during homologous recombination?

Answer 13

sections of the chromosome are ‘swapped’, giving new allele combinations

Question 13

How does meiosis generate variation?

Answer 13

through crossing over

Question 13

At what stage of Meiosis 1 are crossovers visible?

Answer 13

diplotene stage - they are still in place but chromatids have slightly separated - sites of crossovers can be seen.

Question 13

What process relies on chromatids being lined up correctly that identical (or nearly-identical) sequences can be accessed?

Answer 13

homologous recombination

Question 13

What ‘deliberately’ generates double-stranded breaks?

Answer 13

a specialised enzyme

Question 13

At a molecular level, what are crossovers?

Answer 13

sites of genetic exchange between homologous sequences on non-sister chromatids

Question 13

What are chiasmata?

Answer 13

points of contact between non-sister chromatids of homologous chromosomes in Meiosis 1