meiosis

Question 1

define meiosis

Answer 1

a two-staged cell division in sexually reproducing organisms that produces four genetically distinct daughter cells each with half the number of chromosomes of the parent cell

Question 2

what does meiosis result in

Answer 2

four genetically distinct haploid gametes

Question 3

what are the stages of meiosis

Answer 3

1) interphase
2) meiosis I
3) meiosis II
4) cytokinesis

Question 4

Draw a diagram showing the mass of DNA per cell/AU over time during meiosis

Answer 4

refer to PG 114 of text book

Question 5

what are the stages of meiosis

Answer 5

1) prophase I
2) metaphase I
3) anaphase I
4) telophase I
5) Prophase II
6) metaphase II
7) anaphase II
8) telophase II

Question 6

what is meant by the term synapsis

Answer 6

the pairing of chromosomes

Question 7

what does synapsis form

Answer 7

A bivalent

Question 8

outline what occurs in prophase I of meiosis

Answer 8

1) maternal and paternal chromosomes form a homologous pair via synapsis- this forms a bivalent
2) chromosomes coil and shorten becoming condensed
3) centrioles migrate to opposite poles
4) spindle fibres are formed
5) a chiasmata is formed via crossing over of non-sister chromatids in the bivalent allowing recombination of genetic material from parents producing new alleles and genetic variation
6) nuclear envelope disintegrates and the nucleolus disappears

Question 9

what is a chiasmata

Answer 9

occurs during crossing over of non-sister chromatids and is the site at which chromosomes exchange DNA during genetic crossing over

Question 10

outline the process of metaphase I in meiosis

Answer 10

1) spindle fibres attach to the centromere and moves chromosomes to the equator
2) the bivalents arrange themselves randomly at the equator, with either one of the homologous pair facing either pole- random assortment

Question 11

outline anaphase I of meiosis

Answer 11

1) the chromosomes in each bivalent sperate as the spindle fibres shorten
2) one of each pair (one whole chromosomes) is pulled to one pole and the other the opposite pole
3) due to random assortment during metaphase I there is a random mixture of maternal and paternal chromosomes

Question 12

outline telophase I of meiosis

Answer 12

1) the cytoplasm separates
2) the nuclear envelope reforms and the nucleolus reappears
3) each nucleolus now contains half the number of original chromosomes ( 2 chromosomes, haploid chromosomes)

Question 13

outline cytokinesis in meiosis I

Answer 13

the cytoplasm divides forming two haploid cells- cells containing one complete set of chromosomes

Question 14

how does crossing over introduce genetic variation in meiosis

Answer 14

1) crossing over of non-sister chromatids of the bivalent forming a chiasma where segments of DNA can be exchanged from one chromatid to another= produces a new combination of alleles

Question 15

how does independent assortment of chromosomes introduce genetic variation in meiosis

Answer 15

homologous chromosomes arrange themselves randomly at the equator of the cell during metaphase I, therefore, different combinations of maternal and paternal chromosomes are pulled to either pole during anaphase- genetic variation in gametes haploid cells after cytokinesis

Question 16

outline prophase II in meiosis

Answer 16

1) chromosomes condense and become visible
2) centrioles replicate and move to opposite poles
3) centrioles organize a new spindle fiber at a right angle to the old spindle in meiosis I
4) nuclear envelope disintegrates and the nucleolus disappears

Question 17

outline metaphase II in meiosis

Answer 17

1) spindle fibers pull chromosomes to the equator via the centromere
2) random assortment occurs and as the chromatids of the chromosomes can face either pole

Question 18

outline anaphase II

Answer 18

1) spindle fibers contract separating the centromeres dividing the chromatids
2) the chromatids are pulled to opposite poles of the cell centromere first
3) chromatids are now chromosomes once again

Question 19

outline telophase II in meiosis

Answer 19

1) chromosomes lengthen and are no longer visible
2) spindle fibers disintegrate
3) nuclear envelope and nucleolus reform

Question 20

outline cytokinesis in meiosis II

Answer 20

cytoplasm divides producing four genetically different haploid cells

Question 21

what is the significance of meiosis

Answer 21

1) keeps chromosome number constant through generation

2) generates genetic variation

Question 22

how is genetic variation intruded during metaphase I and metaphase II through independent assortment

Answer 22

metaphase I- daughter cells contain different combinations f maternal and paternal chromosomes

metaphase II- daughter cells have different combinations of chromatids