Lecture 7 - Chromosome Segregation

Question 1

How do you get genes from your parents?

Answer 1

Genes from both parents undergo meiosis and enter daughter cells. These then undergo mitosis

Question 2

What can happen if you undergo chromosomes mis-segregation in somatic cells?

Answer 2

Cancer

Question 3

What happens is chromosome mis-segregation happens in female meiosis in human oocytes?

Answer 3

Infertility, miscarriage, birth defects

Question 4

Mechanism of chromosomes segregation - anatomy of chromosomes - what is the key features?

Answer 4

2 double stranded dna

Question 5

Mechanism of chromosomes segregation - what is the main attachment site between sister chromatids?

Answer 5

Centromeres

Question 6

Mechanism of chromosomes segregation - where do spindle fibres attach?

Answer 6

Kinetochores

Question 7

During mitosis what holds sister chromatids together?

Answer 7

Cohesin

Question 8

Do all chromosomes need to be attached to both poles? If so, why?

Answer 8

Yes because they cannot separate and therefore will send of wait signals until both poles are attached

Question 9

What happens if both poles attach correctly to the chromatids

Answer 9

The cohesin is destroyed and the sister chromatids enter anaphase which means they can be pulled apart

Question 10

What is the structure of cohesin?

Answer 10

4 subunits which form a ring structure to embrace the DNA after dna replication..

Question 11

What happens to the cohesin in anaphase?

Answer 11

One of the subunits is destroyed by a specific protease during anaphase

Question 12

When is cohesin established?

Answer 12

During s phase

Question 13

What is the difference between mitosis and meiosis in terms of cell numbers?

Answer 13

Mitosis - 1x diploid cell creates 2x diploid cells,

Meiosis (two division) - 1x diploid cell makes 4x haploid cells

Question 14

What is a diploid?

Answer 14

Chromosomes are in a pair - they are identical apart form X and Y in males

Question 15

What is the difference between homologous chromosomes and sister chromatids?

Answer 15

Homologous - one from mother one from father and made form a pair of sister chromatids = may have a different genetic makeup

Sister chromatids - a duplicate of the same chromatids = identical

Question 16

What is the main point of mitosis?

Answer 16

To separate sister chromatids into 2 daughter cells.

Question 17

How does meiosis 1 work?

Answer 17

1x diploid cell = sister chromatids pair with other sister chromatids and swap genetic information. Then the 2 pairs of sister chromatids separate (e.g II and II join IIII then swap genetic information and then split back into II and II

Question 18

How does meiosis 2 works?

Answer 18

The haploid cells have swapped genetic information and then each daughter cell sister chromatids split and form 4 daughter cells.

E.g. II and II goes to I and I and I and I.

Question 19

What happens once meiosis is finished?

Answer 19

Two haploid cells form egg and sperm come together to make a diploid zygote

Question 20

How does meiosis create diversity?

Answer 20

Segregation of homologous chromosomes and recombination between homologous chromosomes

Question 21

How does Segregation of homologous chromosomes create diversity?

Answer 21

Ignoring recombination any chromosomes can go into any daughter cell with any other chromosome

Question 22

How does recombination between homologous Chromosomes create diversity?

Answer 22

A chromosomes could have good and bad parts and they could recombine with another chromosomes which has both good and bad parts to make a fully good or a fully bad chromosomes

Question 23

Meiosis stages - what happens during prophase 1?

Answer 23

Recombine homologous chromosomes - exchange of genes and crossing over occurs here

Question 24

In prophase 1 what is the synaptonemal complex?

Answer 24

This stabilises homologous chromosomes pairings=ands promote recombination. It contains a recombination nodule

Question 25

What are the 5 stages of prophase 1 and their morphology of SC?

Answer 25

Leptotene - SC starts forming
Zygotene
Pachytene - SC fully formed
Diplotene - SC disassembled
Diakinesis - chromosomes condense

Question 26

What happens after the chromosomes has condensed in prophase 1?

Answer 26

They attaché it poles - sister kinetochores attach to the same pole

Question 27

What holds homologous chromosomes together (not sister chromatids)?

Answer 27

Chiasmata

Question 28

In meiosis 1 what cohesin is kept?

Answer 28

The ones at the centromeres so the sister chromatids will stay together even when the homologous pair it was exchanging DNA with goes away

Question 29

What happens to make the cohesin holding the sister chromatids go away?

Answer 29

Kinetochores attach to opposite poles

Question 30

The difference between meiosis 1 and meiosis II sister Kinetochores?

Answer 30

At 1 Kinetochores attach to same pole at 2 they attach to different poles

Question 31

The difference between meiosis 1 and meiosis II cohesin at centromeres?

Answer 31

1 - protected and during 2 is destroyed