Topic 3.3: Meiosis

Question 1

Meiosis

Answer 1

Reduction division of a diploid cell to produce four haploid cells (gametes) that are genetically distinct

Question 2

Cellular divisions in meiosis

Answer 2

a) Meiosis I separates homologous chromosomes

b) Meiosis II separates sister chromatids

Question 3

Mitosis vs Meiosis (Discopug)

Answer 3

a) Divisions
b) Independent assortment
c) Synapsis
d) Crossing over
e) Outcome
f) Ploidy
g) Use
h) Genetics

Question 4

a) Divisions
b) Independent assortment
c) Synapsis
d) Crossing over
e) Outcome
f) Ploidy
g) Use
h) Genetics

Answer 4

a) 1 | 2
b) No | Yes (Metaphase I)
c) No | Yes
d) No | Yes (Prophase I)
e) 2 | 4
f) Diploid | Haploid
g) Body | Sex
h) Identical | Variation

Question 5

DNA Duplication in Meiosis

Answer 5

DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids

Question 6

Stages of Meiosis

Answer 6

a) P-I
b) M-I
c) A-I
d) T-I
e) P-II
f) M-II
g) A-II
h) T-II

Question 7

Prophase I

Answer 7

a) Chromosomes condense
b) Nuclear membrane dissolves
c) Homologous chromosomes form bivalents
d) Crossing over occurs

Question 8

Metaphase I

Answer 8

a) Spindle fibres from opposing centrosomes connect to bivalents
b) Bivalents align along the middle of the cell

Question 9

Anaphase I

Answer 9

a) Spindle fibres contract and split the bivalent

b) Homologous chromosomes move to opposite poles of the cell

Question 10

Telophase I

Answer 10

a) Chromosomes
decondense
b) Nuclear membrane may reform
c) Cell divides (cytokinesis)

Question 11

Prophase II

Answer 11

a) Chromosomes condense
b) Nuclear membrane dissolves
c) Centrosomes move to opposite poles (perpendicular to before)

Question 12

Metaphase II

Answer 12

a) Spindle fibres from opposing centrosomes attach to chromosomes (at centromere)
b) Chromosomes align along the cell equator

Question 13

Anaphase II

Answer 13

a) Spindle fibres contract and separate the sister chromatids
b) Chromatids (now called chromosomes) move to opposite poles

Question 14

Telophase II

Answer 14

a) Chromosomes decondense
b) Nuclear membrane reforms
c) Cells divide (cytokinesis) to form four haploid daughter cells

Question 15

Crossing over

Answer 15

a) Crossing over occurs via synapsis in Prophase I
b) Homologous chromosomes form bivalents (or tetrads)
c) As a result of this exchange of genetic material, new gene combinations are formed on chromatids (recombination)

Question 16

Chiasmata

Answer 16

The points where genetic information has been exchanged between the homologous pair

Question 17

Recombinants

Answer 17

The non-sister chromatids that have exchanged DNA

Question 18

Random Assortment

Answer 18

a) The homologous pairs orient randomly in Metaphase I

b) This means there is an equal chance of a resulting gamete containing either the maternal or paternal chromosome

Question 19

Random assortment and potential gamete combinations in humans

Answer 19

As humans have a haploid number of 23, consequently there are 2^23 potential gamete combinations (>8 million)

Question 20

What does the halving of the chromosome number allow?

Answer 20

a) It allows for a sexual life cycle with the fusion of gametes.
b) This acts as a further source of genetic variation

Question 21

Three main sources of genetic variation from sexual reproduction

Answer 21

a) Crossing over (in prophase I)
b) Random assortment of chromosomes (in metaphase I)
c) Random fusion of gametes from different parents

Question 22

Non-disjunction

Answer 22

Chromosomes failing to separate, resulting in gametes with extra or missing chromosome

Question 23

When may the failure of chromosomes to separate occur?

Answer 23

a) Failure of homologues in Anaphase I (4 affected daughter cells)
b) Failure of sister chromatids in Anaphase II (2 daughter cells being affected)

Question 24

Down Syndrome

Answer 24

a) If a gamete with an extra chromosome fuses with a normal gamete, the resulting zygote will have three copies
b) Trisomy 21

Question 25

How does parental age influence the chances of non-disjunction?

Answer 25

Older parents are at a higher risk of non-disjunction events