lecture 14 meiosis

Question 1

What happens in prophase 1

Answer 1

Homologous chromosomes are pairs of chromosomes align and form synapses between them.
These synapses allow for crossing over to occur at the chiasmata, this happens between non-sister chromatids.
Centrosome movement, spindle fibres begin to form, the nuclear envelope breaks down all like mitosis.
Chromosomes begin to condense in this phase
Later in prophase one, the spindle microtubules connect to the kinetochores at the centre of each homologous pair. One on each homolog

Question 2

what happens in metaphase 1:

Answer 2

homologous pairs of chromosomes line up on the metaphase plate, with their chiasmata being directly on the metaphase plate line.
Both chromatids of one homolog are attached to a kinetochore and one microtubule spindle attaches to one kinetochore, the microtubule is effectively attached to two chromatids.

Question 3

describe anaphase 1:

Answer 3

Non-kinetochore spindle fibres extend and the kinetochore spindle fibres retract.The sister chromatids remain, as homologous pairs are separated.
This process can be called disjunction
Proteins that are responsible for sister chromatid cohesion, the chiasmata, along the chromatid arms break down, allowing the two homologs to separate.
Sister cohesion continues at the centromere of the homolog which causes the homolog to be moved to the pole as a unit.

Question 4

whats disjunction

Answer 4

this is where the chiasmata junctions are broken.

Question 5

describe telophase 1

Answer 5

splits the two cells
A cleavage furrow begins to form
Spindle fibres disappear
Makes two diploid cells
At telophase one each half of the cell has two sets of each duplicated chromosome.
Each chromosome has two sister chromatids, these sister chromatids may have non-sister
Chromatid regions due to crossing over
Cytokinesis occurs at the same time as telophase to form the two daughter cells.
The cleavage furrow forms in animal cells and cell plate for plant cells

Question 6

what is meiosis two similar to

Answer 6

mitosis

Question 7

what doesn’t happen before meiosis 2

Answer 7

there is no DNA replication before this part of meiosis

Question 8

what happens in prophase 2

Answer 8

Prophase 2:
Spindle fibres form, not connected at this time
In late prophase 2 the homologous sister chromatids move towards the metaphase plate

Question 9

describe metaphase 2

Answer 9

Chromosomes are centred at the metaphase plate like they are in mitosis metaphase
Because of crossing over( which only occurs in meiosis one) the two sister chromatids on the chromosome aren’t genetically identical anymore
The microtubule spindle fibres attach to the kinetochores of each chromosome, same as metaphase of mitosis

Question 10

describe anaphase 2

Answer 10

Breakdown of proteins holding the sister chromatids together at the centromere allows the chromatids to separate as the spindle fibres shorten, pulling chromosomes to opposite sides of the cell.

Question 11

describe telophase 2

Answer 11

Nuclei form and the chromosomes begin to condense to fit in said nuclei.
Cytokinesis begins to occur
This makes 4 unique daughter cells that are haploid, half the needed chromosomes, one copy of each.

Question 12

what is sexual cycle

Answer 12

people make gametes, gametes fertilise to make a zygote, zygote then mitosis to make a people