Cell division

Question 1

mitosis

Answer 1

somatic cell division, in which the nucleus also divides
produces 2 daughter cells with the same number of chromosomes (23 pairs)
separation of chromatids, one of which has been replicated from the other in the S phase

Question 2

how long does mitosis last?

Answer 2

1-2 hours, continuous process

Question 3

what are the phases in mitosis?

Answer 3

prophase

prometaphase

metaphase

anaphase

telophase

Question 4

prophase

Answer 4

chromosomes condense and mitotic spindle begins to form. 2 centrioles form in each cell, from which microtubules radiate as they move towards opposite ends of the cell

Question 5

prometaphase

Answer 5

nuclear membrane begins to disintegrate, allowing chromosomes to spread around the cell

each chromosome becomes attached at its centromere to a microtubule of the mitotic spindle

Question 6

metaphase

Answer 6

chromosomes become aligned along the equatorial plane, each one attached to the centriole

maximally contracted and most easily visible

chromatids separate longitudinally but are attached at the centromere (not undergone division yet)

Question 7

anaphase

Answer 7

centromere of each chromosome divides longitudinally and 2 daughter chromatids separate to opposite poles

Question 8

telophase

Answer 8

chromatids are independent chromosomes consisting of a single double helix

two groups of daughter chromosomes become enveloped in a new nuclear membrane

cytokinesis - nuclear membrane separates

Question 9

what does each daughter cell contain?

Answer 9

complete diploid chromosome complement

Question 10

interphase

Answer 10

period between successive mitoses

Question 11

how long does interphase last in rapidly dividing cells?

Answer 11

16-24 hours

Question 12

components of interphase

Answer 12

G1, G2, S, G0

Question 13

G1 phase

Answer 13

chromosomes become thin and extended

variation in length - responsible for variation in generation time between different cell populations

cells that have stopped dividing usually arrest in this phase and enter G0

Question 14

S phase

Answer 14

when DNA replication occurs and chromatin of each chromosome is replicated
formation of 2 chromatids
DNA replication occurs at multiple points on a chromosome

Question 15

sex chromatin

Answer 15

Barr body

one of the X chromosomes is always late in replicating - visualised during interphase in female somatic cells

cells from buccal mucosa - buccal smear

Question 16

when does meiosis occur?

Answer 16

final stage of gamete formation

Question 17

how does meiosis differ from mitosis?

Answer 17

mitosis results in each daughter cell having a diploid chromosome complement (46)
in meiosis the diploid count is halved so each mature gamete receives a haploid complement (23)

mitosis occurs in somatic cells and in early cell divisions in gamete formation. meiosis occurs only in final division of gamete maturation

mitosis is a 1 step process, meiosis has 2

Question 18

what is meiosis sometimes referred to?

Answer 18

reduction division - chromosome number is halved

Question 19

prophase 1

Answer 19

chromosomes enter phase already split longitudinally into 2 chromatids joined at the centromere

homologous chromosomes pair and exchange of homologous segments occurs between non-sister chromatids

Question 20

recombination

Answer 20

crossing over

exchange of homologous segments between chromatids occurs

Question 21

prophase 1 in the male

Answer 21

pairing occurs between homologous segments of the X and Y chromosomes at the tip of their short arms - this portion of each chromosome is the pseudoautosomal region

Question 22

five stages of prophase 1

Answer 22

leptotene

zygotene

pachytene

diplotene

diakinesis

Question 23

leptotene

Answer 23

chromosomes become visible as they start to condense

Question 24

zygotene

Answer 24

homologous chromosmes align directly opposite eachother (synapsis) and are held together at points along their length by filamentous structures (synaptonemal complexes)

Question 25

synapsis and synaptonemal complexes

Answer 25

homologous chromosomes aligning directly opposite eachother filamentous structures holding chromosomes together

Question 26

pachytene

Answer 26

each pair of homologous chromosomes (bivalent) becomes tightly coiled. crossing over occurs

Question 27

bivalent

Answer 27

pair of homologous chromosomes

Question 28

diplotene

Answer 28

homologous recombinant chromosomes begin to separate but remain attached at points where crossing over has occurred (chiasmata)

Question 29

chiasmata

Answer 29

points on chromosomes where recombination has occured. small, medium and large chromosomes have 1, 2 adn 3 chiasmata respectively - approx. 40 recombination events per meiosis per gamete

Question 30

diakinesis

Answer 30

separation of homologous chromosome pairs proceeds as chromosomes become maximally condensed

Question 31

metaphase 1

Answer 31

nuclear membrane disappears and chromosomes align along equatorial plane, attached to the spindle

Question 32

anaphase 1

Answer 32

chromosomes separate to opposite poles of the cell as the spindle contracts

Question 33

telophase 1

Answer 33

each set of haploid chromosomes has separated completely to opposite ends of the cell, and cleaves into 2 new daughter gametes (secondary spermatocytes or oocytes)

Question 34

meiosis 2

Answer 34

each chromosome becomes aligned along the equatorial plane and splits longitudinally, forming 2 new daughter gametes - spermatids or ova

Question 35

consequences of meiosis

Answer 35

facilitates halving of the diploid number of chromosomes so each child receives half of its chromosome complement from each parent potential for genetic diversity

Question 36

how does meiosis have potential to generate genetic diversity?

Answer 36

when the bivalents separate, they do so independently of each other - each gamete receives a selection of parental chromosomes likelihood that 2 gametes contain same chromosomes is 1 in 8 million chromatid contains portions of DNA derived from both parental homologous chromosomes

Question 37

what is gene shuffling?

Answer 37

dispersion of DNA into different gametes

Question 38

clinical relevance of mitosis

Answer 38

detecting chromosomal abnormalities categorising tumours as benign or malignant grading malignant tumors

Question 39

clinical relevance of the mitotic spindle

Answer 39

taxol | vinca alkaloids - vinblastine, vincristine

Question 40

clinical relevance of anaphase

Answer 40

colchicine like drugs

Question 41

clinical relevance of spindle poles

Answer 41

ispinesib