mitosis and meiosis

Question 1

what is independent segregation/ assortment?

Answer 1

occurs In metaphase 1
maternal and paternal chromosomes can be positioned either side of the equator of the cell
This is random and independent for each homologous pairs
results in cells with different combinateation od maternal and paternal chromosomes

Question 2

What happens in telophase

Answer 2

chromosomes uncoil/ decondense and nuclear envelope reforms around DNA

Question 3

what happens in metaphase 2?

Answer 3

chromosomes line up at the equator of cell and attach to spindle fibres by the centromere

Question 4

what happens in prophase 2

Answer 4

chromsomes condense and become visible
spindle fibres form

Question 5

what happens in the S phase of mitosis

Answer 5

DNA replication

Question 6

what happens in prophase 1

Answer 6

chromosomes condense and become visible,
homologous chromosomes attach to each other at chiasmata ( non sister chromosomes join together)
forming bivalents spindle fibres form

Question 7

what happens in prophase

Answer 7

chromosomes condense and become visible due to DNA becoming associated with histones, nuclear membrane and nucleolus disappears, spindle fibres start to form

Question 8

what happens in telophase 1

Answer 8

chromosomes uncoil
spindle fibres break down
haploid nuclei have formed

Question 9

How does meiosis increase genetic variation

Answer 9

independent segregation/ assortment
and crossing over
increasing combination of alleles
random fertilisation of gametes

Question 10

What happens in the G phase of interphase

Answer 10

cell increases in size and new organelles are made in preparation for mitosis

Question 11

what happens in telophase 2

Answer 11

chromosomes uncoil
spindle fibres break down

Question 12

what is crossing over

Answer 12

occurs in prophase 1
exchanged when the chiasmata break
results in new combinations of alleles on the chromatids

Question 13

what happens in prophase 1

Answer 13

chromosomes condense and become visible
homologous chromosomes attach to each other at chiasmata (non- sister chromosomes join together)
forming bivalents, spindle files form

Question 14

what are the 4 stages of mitosis

Answer 14

prophase
metaphase
anaphase
telophase

Question 15

what happens in anaphase

Answer 15

spindle files contract, pulling apart centromeres and pulling sister chromatids apart, going to opposite poles of the cell

Question 16

what happens in metaphase

Answer 16

chromosomes line up at the equator of the cell, attached to the spindle fibres of the centromere, arranged as pairs of homologues chromosomes

Question 17

what happens in anaphase 2

Answer 17

chromosomes seperate, and chromatids are pulled to the poles of the cell
spindle fibres contract, pulling the chromatids by the centromeres

Question 18

what does cytokinesis occur

Answer 18

during telphase

Question 19

what happens in anaphase 1

Answer 19

homologous pairs of chromosomes are pulled to poles of the cell,
spindle fibres contract, pulling the chromosomes by the centromere

Question 20

summarise mitosis

Answer 20

2 daughter cells produced which are diploid and genetically identical over 1 nuclear division

Question 21

what happens in metaphase 1

Answer 21

homologous pairs of chromosomes attach to spindle fibres at the equator of the cell

Question 22

summarise meisois

Answer 22

4 daughter cells produced, which are haploid and genetically different, two nuclear divisors

Question 23

  Name the three phases of mitosis shown by C, D and E on the figure above.
Describe the role of the spindle fibres and the behaviour of the chromosomes during each of these phases.

Answer 23

C = prophase and
D = metaphase and
E = anaphase;
2. (In) prophase, chromosomes condense;
Accept chromatin for ‘chromosomes’ and for ‘condense’, shorten and thicken
3. (In) prophase OR metaphase, centromeres attach to spindle fibres;
4. (In) metaphase, chromosomes/pairs of chromatids at equator/centre of spindle/cell;
5. (In) anaphase, centromeres divide;
6. (In) anaphase, chromatids (from each pair) pulled to (opposite) poles/ends (of cell);
Accept for ‘chromatids’, chromosomes but reject homologous chromosomes
7. (In) prophase/metaphase/anaphase, spindle fibres shorten;
If mark point 1 is not credited = 4 max
Do not carry forward error from 1.
Accept letters for stages as indicated in 1.
Accept for ‘shorten’, contract

Question 24

Describe the appearance and behaviour of chromosomes during mitosis.

Answer 24

(During prophase)
1. Chromosomes
coil / condense / shorten / thicken / become visible;
2. (Chromosomes) appear as (two sister) chromatids joined at the centromere;
(During metaphase)
3. Chromosomes line up on the equator / centre of the cell;
4. (Chromosomes) attached to spindle fibres;
5. By their centromere;
(During anaphase)
6. The centromere splits / divides;
7. (Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell / separate;
(During telophase)
8. Chromatids / chromosomes
uncoil / unwind / become longer / thinner.

Question 25

Describe the behaviour of chromosomes during mitosis and explain how this results in the production of two genetically identical cells.

Answer 25

1 chromosomes shorten / thicken / supercoiling;
2 chromosomes (each) two identical chromatids / strands / copies
(due to replication);
3 chromosomes / chromatids move to equator / middle of the spindle / cell;
4 attach to individual spindle fibres;
5 spindle fibres contract / centromeres divide / repel;
6 (sister) chromatids / chromosomes (separate)
move to opposite poles / ends of the spindle;
7 each pole / end receives all genetic information /
identical copies of each chromosome;
8 nuclear envelope forms around each group of chromosomes /
chromatids / at each pole;