meiosis

Question 1

what is meiosis?

Answer 1

the term meiosis was coined by farmer and Moore, “Meio” means to lessen. this division was by Wenn Benidin Winiwarter and strassburger .it contains two sequential nuclear division but only one cycle of DNA replication, which forms 4 haploid cells.

Question 2

where does meiosis occur?

Answer 2

in sexually reproducing animals. germs cells undergo meiosis to produce gametes

Question 3

what are the two divisions of meiosis?

Answer 3

1) meiosis 1: it is a reductional division i.e DNA content reduces by half
2) meiosis 2: it is an equational division i.e DNA content remains the same

Question 4

what are the divisions under meiosis 1?

Answer 4

1) prophase 1:
a) leptotene
b) zygotene
c) pachytene
d) diplotne
e) diakenisis
2) metaphase 1
3) anaphase 1
4) telophase 1

Question 5

explain leptotene.

Answer 5

1) condensation and coiling of chromatin occurs
2) chromosomes gradually becomes visible under a microscope
3) bouquet stage

Question 6

explain zygotene.

Answer 6

1) homologous chromosomes start to pair this is known as synapsis. and forms a bivalent
2) formation of the synaptonemal complex occurs

Question 7

what are homologous chromosomes?

Answer 7

they are chromosomes identical in shape size and structure. one of the homeologous chromosomes is maternal and the other is paternal.

Question 8

why does the formation of the synaptonemal complex occur?

Answer 8

help is stabilising the homologous chromosomes until the crossing is over.

Question 9

explain pachytene.

Answer 9

1) the synapsed chromosomes continue to m become thick and short. the 4 chromatids form a tetrad
2) two non-sister chromatids start to cross over ie they start to exchange genetic matter, this done by breakage and reunion of chromosomal segments
3) the recombination of the chromosome is done with the help of recombinase enzyme.

Question 10

explain diplotene.

Answer 10

1) synaptonemal complex disappears
2) x shaped structure named chiastama forms
3) in oocytes(eggs) of some vertebrates, this stage lasts for months or years. the longest phase of prophase
4) aka dictyotene stage

Question 11

explain diakinesis.

Answer 11

1) criminalisation of chiasmata due to tight condensation of chromosomes,
2) spindle appears
3) nuclear membrane and nucleolus disappears, nuclear envelop disintegrates

Question 12

explain metaphase 1.

Answer 12

1) two equatorial / metaphasic plates form
2) the centromere arrange themselves on the equatorial plates, forming a double metaphasic plate
3) there is no fixed direction in which the chromosomes should face
4) the distribution of the bivalent chromosomes are random
4) microtubules from the spindle fibres attach to the centromere facing towards it.

Question 13

explain anaphasic 1.

Answer 13

1) the two homologous chromosomes, separate and moves toward their respective poles, centromere does not split
2) there is a reduction of genetic material in daughter cells and this occurs in anaphase 1

Question 14

explain telophase 1.

Answer 14

1) the chromosomes reach their respective poles and uncoils
2) nuclear membrane, nuclear envelop and nucleolus reappears
3) spindle fibres disappears

Question 15

explain cytokinesis 1.

Answer 15

1) 1 diploid cell forms 2 haploid cells

Question 16

wha t is interkinesis?

Answer 16

interkinesis or intramieotic interphase is a gap between meiosis 1 and 2, present between telophase 1 and prophase 2. there is no DNA replication during this phase. RNA and protein required for meiosis 2 are synthesised in this stage, centriole replication occurs in animal cells.

Question 17

explain prophase 2.

Answer 17

1) condensation of chromosomes
2) nuclear membrane, nucleolus and nuclear envelop disappears
3) initiation of spindle apparatus

Question 18

explain metaphase 2.

Answer 18

1) one equotorial or metaphasic plate appears

2) chromosomes align themselves on equatorial plate

Question 19

explain anaphase 2.

Answer 19

1) centromere splits

2) chromosmes moves towards thier respective poles

Question 20

what is the terminalisation of chiasmata

Answer 20

movement of chiasmata toward the tip of the chromosomes due to condensation

Question 21

explain telophase 2.

Answer 21

1) disintegration of spindle fibers

2) nuclear membrane , nucleolus and nuclear envelop reappears.

Question 22

explain cytokinesis 2.

Answer 22

1) cleavage furrows and moves toward the center in animals , and cell plate forms in plant cells
2) forms 4 haploid daughter cells

Question 23

explain the significance of meiosis.

Answer 23

1) formation of gametes
2) maintenance of chromosome number
3) introduction of variation

Question 24

distinguish between meiosis and mitosis

Answer 24

study from TB

Question 25

what is the formulae used to find the number of meiotic division required to form n haploid cells?

Answer 25

n /4

Question 26

what is the formulae used to find the number of meiotic division required to form n diploid cells?

Answer 26

n + n/4

Question 27

how is variation introduced in meiosis?

Answer 27

1) crossing over

2) random distribution of maternal and paternal chromosomes