Meiosis

Question 1

What is meiosis

Answer 1

Meiosis is the cell division whereby a diploma cell (somatic cell) undergoes two cell divisions, and divides to form four dissimilar haploid cells(sex cells).

Question 2

Diploid cells

Answer 2

Have two sets of chromosomes, where each chromosome has a homologous partner.

Question 3

Haploid cells

Answer 3

Only have one set of chromosomes. Chromosomes in haploid cells have no homologous partner.

Question 4

What happens before meiosis begins

Answer 4

Before meiosis begins (during) interphase, DNA replication takes place. The result is two sets of chromosomes consisting of two identical chromatids joined together with a centromere.

Question 5

The process of meiosis in animal cells

Answer 5

⚡Meiosis is the type of cell division used to produce gametes or sex cells (sperm and egg cellc). A cell undergoing meiosis will divide twice (meiosis I and meiosis II).

Question 6

What happens in Meiosis I

Answer 6

👑in the first meiotic division, the number of cellc is doubled,
but the number of chromosomes is not. This results in half
as many chromosomes per cell.

Question 7

What happens in Meiosis II

Answer 7

👑 in the second meiotic division, the number of chromosomes does not get reduced.

Question 8

First meiotic division

📣Prophase 1

Answer 8

⚡chromosomes shorten and become visible as two
chromatids joined by a centromere.
⚡homologous pairs of chromosomes are now visible.
⚡the nuclear membrane and nucleolus disappear.
⚡The spindle starts to form.
⚡Chromatids from each homologous pair touch. The point
where they touch is called a chiasma.
⚡DNA is crossed over (swopped) at the chiasma
⚡The spindle continues to form.

Question 9

First meiotic division

📣Metaphase 1

Answer 9

➡️The spindle extrand across the whole cell.
➡️The homologous chromosomes line up along the equator
of the spindle in their homologous pairs.
➡️One chromosome of each pair lies on iether side of the
equator.
➡️The centromere of each chromosome attaches to the
spindle fibres.

Question 10

First meiotic division

📣Anaphase1

Answer 10

👑The spindle fibres shorten an pull each chromosome of

each chromosome pair to opposite poles of the cell.

Question 11

First meiotic division

📣Telophase

Answer 11

🔌The chromosomes reach the poles of the cell.
🔌Each pole has half the number of chromosomes present in
the original cell.
🔌The cell membrane constricts and divides the cytoplasm
in half to form two cells.

Question 12

Second meiotic division

✳️Prophase 2

Answer 12

🍭Each cell formed during meiosis 1 now divides again.

🍭A spindle forms in each of the new cells.

Question 13

Second meiotic division

✳️Metaphase 2

Answer 13

🍭 Individual chromosomes line up at the equator of each cell, with the centromeres attached to the spindle fibres.

Question 14

Second meiotic division

✳️Anaphase 2

Answer 14

🍭The spindle fibres start to contract.

🍭The centromeres split and daughter chromosomes /chromatids are pulled to the opposite poles of each cell.

Question 15

Second meiotic division

✳️Telophase 2

Answer 15

🍭The daughter chromosomes/chromatids reach the poles and a new nucleus forms.
🍭The cell membrane of each cell constricts and the cytoplasm divides into two cells.
🍭Four haploid daughter cells are formed.
🍭Each daughter cell has half the number of chromosomes of the original cell.
🍭The daughter cells are genetically different from each other.

Question 16

An easy way to remember the events of meiosis is to use the word IPMAT

Answer 16

📣I - Interphase
📣P- Prophase
📣M - Metaphase 
📣A - Anaphase 
📣T - Telophase

Question 17

IPMAT - I

Answer 17

I - Interphase

❇️I for in between: The part of the life cycle of the cell that is in between cell divisions

Question 18

IPMAT - P

Answer 18

P- Prophase
❇️P for preparation: The chromosomes prepare for meiosis by untangling and becoming clearly visible. Crossing over also takes place.

Question 19

IPMAT - M

Answer 19

M- Metaphase

❇️M for middle: the chromosomes move to the ‘middle’ (equator).

Question 20

IPMAT - A

Answer 20

A - Anaphase

❇️A for apart: The chromosomes /chromatids move apart /move to the poles.

Question 21

IPMAT - T

Answer 21

T- Telophase

❇️T for terminal: The final phase of meiosis 1/meiosis 2.

Question 22

The significance of Meiosis

Answer 22

1. It reduces the number of chromosomes by half, in other words from diploid to haploid. This ensures that sex cells have half the number of chromosomes of other somatic cells so that when fertilization occurs the zygote formed has the
   correct number of chromosomes. It balances the doubling effect of fertilization.
2. Crossing over introduces genetic variation. Genetic variation results in offspring that are better adapted to a particular environment and ensures that they will have a better chance of survival.

Question 23

Abnormal meiosis

Answer 23

➡️Sometimes mistakes occur during the process of meiosis.
➡️This can happen in Anaphase 1 where the homologous chromosomes may not separate. Also called non-disjunction.
➡️It can also happen in Anaphase 2 when there is non-disjunction of the sister chromatids.
➡️If there is non-disjunction of chromosome pair 21 in humans it leads to the formation of an abnormal gamete with an extra copy of chromosomes 21.
➡️If there is fusion between a normal gamete and an abnormal gamete (with extra copy of chromosomes 21) it leads to Down Syndrome.

Question 24

Differences between meiosis 1 and meiosis 2

Answer 24

Meiosis 1-🍭 meiosis 2-❇️

1.🍭The chromosomes arrange at the equator of the cell in homologous pairs.
❇️Chromosomes line up at the equator of the cell individually.
2.🍭Whole chromosomes move to the opposite poles of the cell.
❇️Daughter chromosomes /chromatids move to opposite poles of the cell.
3.🍭Two cells form at the end of this cell division
❇️Four cells are formed at the end of the cell division.
4.🍭The chromosome number is halved during meiosis 1.
❇️The chromosome number remains the same during meiosis 2.
5.🍭Crossing over takes place.
❇️Crossing over does not take place.