Topic 3.3 Meiosis

Question 1

Meiosis

Answer 1

Meiosis is the reduction division of diploid cell to produce four haploid cells (gametes that are genetically distinct.)
→ It involves two divisions
- Meiosis I separates homologous chromosomes
- Meiosis II separates sister chromatids

Question 2

Crossing Over

Answer 2

Crossing over is the cause for genetic variation.
Crossing over occurs via synapsis in Prophase I.
Homologous chromosomes from bivalents (or tetrads)
Chiasmata represents the points where genetic information has been exchanged between homologous pair.
The non-sister Chromatids that have exchange DNA are recombinants.

Question 3

Sexual Life Cycle

Answer 3

The halving of chromosomes number by meiosis allows a sexual cycle with fusion gametes
→ This acts as a further source of genetic variation

Question 4

Mitosis VS. Meiosis DISCO PUG

Answer 4

Question 5

Random Assortment

Answer 5

The reason for genetic Variation.
The homologous pairs orient randomly in Metaphase I.
This means there is an equal chance of resulting gamete containing either maternal or paternal chromosome.
As humans have a haploid of 23, consequently there are 2^23 potential gamete combinations (>8 million)

Question 6

Non-Disjunction

Answer 6

Non-disjunction refers to chromosomes failing to separate resulting i gametes with extra or missing chromosomes.
The failure to separate may involve the homologous pairs in Anaphase I or the sister chromatids in Anaphase II.
If a gamete with an extra chromosomes fuses with normal gamete, the resulting zygote will have three copies
→ E.g. Trisomy 21 (Down Syndrome)
Studies shows paternal age influences chance of non-disjunkaction
→ Older parents are at higher risk of non-disjunction events

Question 7

Stages of Meiosis I

Answer 7

Is a reduction division (diploid → haploid).
Separates the homologous chromosomes.
Crossing over may occur during Prophase I to create genetically divergent sister chromatids.

Question 8

Stages of Meiosis II

Answer 8

Is akin to a mitotic division (but of haploid cells).
Separates the sister chromatids.
Occurs because DNA is replicated in interphase to create chromosomes with sister chromatids.