Topic 3.3: Meiosis Flashcards Preview

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Flashcards in Topic 3.3: Meiosis Deck (25)
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1

Meiosis

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

2

Cellular divisions in meiosis

a) Meiosis I separates homologous chromosomes
b) Meiosis II separates sister chromatids

3

Mitosis vs Meiosis (Discopug)

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

4

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

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

5

DNA Duplication in Meiosis

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

6

Stages of Meiosis

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

7

Prophase I

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

8

Metaphase I

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

9

Anaphase I

a) Spindle fibres contract and split the bivalent
b) Homologous chromosomes move to opposite poles of the cell

10

Telophase I

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

11

Prophase II

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

12

Metaphase II

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

13

Anaphase II

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

14

Telophase II

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

15

Crossing over

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)

16

Chiasmata

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

17

Recombinants

The non-sister chromatids that have exchanged DNA

18

Random Assortment

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

19

Random assortment and potential gamete combinations in humans

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

20

What does the halving of the chromosome number allow?

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

21

Three main sources of genetic variation from sexual reproduction

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

22

Non-disjunction

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

23

When may the failure of chromosomes to separate occur?

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

24

Down Syndrome

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

25

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

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