Meiosis + Cell cycle

Question 1

What has to happen before meiosis 1 occurs?

Answer 1

Chromosomes are copied in interphase, they are then joined by centromere

Question 2

What happens in early meiosis?

Answer 2

The two chromosomes in a homologous pair come together (crossing over occurs)

Question 3

Explain what happens in crossing over

Answer 3

-Chromatids of the 2 chromosomes wrap around each other
-Tension on chromatids breaks pairs
-Broken parts of chromatids recombine with another chromatid
-Produces recombinant chromosomes

Question 4

What is chiasmata?

Answer 4

The points where the chromatids are joined

Question 5

What are bivalent chromosomes?

Answer 5

They’re the attached pair of chromosomes that result from crossing over

Question 6

Prophase 1
4 points:

Answer 6

-Nuclear membrane breaks down

-Chromosomes condense and become visible

-Homologous chromosomes are attached forming chiasmata, crossing over happens where exchange of alleles occur

-Centrioles move to opposite poles of cell, spindle fibres start to assemble

Question 7

Metaphase 1
2 points:

Answer 7

-Pairs of homologous chromosomes line up in equator of spindle apparatus
-Spindle fibres attach to centromeres

Question 8

Anaphase 1
2 points:

Answer 8

-Spindle fibres shorten
-Homologous chromosomes move towards opposite poles, chiasmata between pair breaks

Question 9

Telophase 1
2 points:

Answer 9

-Nuclear membrane reforms

-Chromosomes uncoil back to chromatin state

Question 10

What happens in meiosis 2?

Answer 10

Exact same process for meiosis 1 however this time centromere of each chromosome divides instead of chiasmata breaking.
Meiosis 1: Pair of chromosomes separated
Meiosis 2:Chromosomes separated into chromatids

Question 11

In what other way can meiosis create genetic variation?

Answer 11

Independent assortment

Question 11

What is independent assortment?

Answer 11

The order by which the pair of homologous chromosomes line up in spindle can be random. During metaphase 1 and 2

We cannot predict whether the paternal or maternal chromosome will end up in which gamete

Question 12

Differences between meiosis 1 and 2

Answer 12

Meiosis 1: Reduces number of chromosomes from parent to daughter cell by half (reduction or heterotypic division)
Meiosis 2: Equalizes number of chromosomes of parent and daughter cells (homotypic division)

Result of meiosis 1 are individual chromosomes and for meiosis 2 are sister chromatids

No crossing over in prophase 2 like in prophase 1

Question 13

What controls rate at which cells divide?

Answer 13

Cyclins (small proteins) which build up and attach to cyclin dependent kinases (CDK).

Question 14

What happens after Cyclin/CDK complex is formed?

Answer 14

Adds a phosphate group to other proteins changing their shapes, signalling the start of the next stage in cell cycle.