Meiosis

Question 1

Where are chromosomes present

Answer 1

Chromosomes are present in nuclei of all living cells.

Question 2

Each chromosome is composed of

Answer 2

a single deoxyribonucleic acid (DNA) molecule wrapped around
proteins called histones.

Question 3

In a non-diving cell

Answer 3

In a non-diving cell, chromosomes exist as long, thin strands called chromatin threads spread through the nucleus. Chromosomes are visible when a cell begins to divide since they become shorter and thicker.

Question 4

Meiosis occurs only in

Answer 4

reproductive organs during production of gametes.

Question 5

Gametogenesis

Answer 5

process of producing gametes

Question 6

oogenesis (ovary)

Answer 6

produces ovum

Question 7

spermatogenesis(testes)

Answer 7

produces sperm.

Question 8

What is formed in meiosis

Answer 8

four genetically non-identical cells are formed. Each cell contains half the number of chromosomes as the parent cell, called the haploid number or n number.

Question 9

What is the haploid number or n number?

Answer 9

Each cell contains half the number of chromosomes as the parent cell, called the haploid number or n number.

Question 10

How many chromosomes do the sex cells have

Answer 10

The sex cells – sperm and ovum, have 23 chromosomes or the haploid number – n, half of a somatic cell.

Question 11

Meiosis is important because it ensures that:

Answer 11

-Each daughter cell has the haploid number of chromosomes. The diploid number can then be restored at fertilization.
- Each daughter cell has a different combination of genes. This leads to variation among offspring which enables species to constantly change and adapt to changing environmental conditions

Question 12

HOMOLOGOUS

Answer 12

the word homologous means that the chromosomes are approx. the same size and contain the same types of genes in the same locations. Chromosomes exist in pairs called homologous pairs. Every human cells has 23 pairs, one member of each pair from maternal origin, and the other of paternal origin. Except the sex chromosomes (X, Y)
members of each pair look alike.

Question 13

BIVALENTS

Answer 13

homologous chromosomes pair forming bivalents.

Question 14

CROSSING OVER

Answer 14

Occurs in Prophase I, where chromosomes are lined up in homologous pairs, they have this way that they can transfer their genetic information and exchange it between each other. Forms recombinant chromosomes and contributes to variety.

Question 15

CENTRIOLES

Answer 15

spindle fibres originate from centrioles. Centrioles only present in animal cells, not plant.

Question 16

Chromosomes duplicate during

Answer 16

interphase

Question 17

PROPHASE (1)

Answer 17

Homologous chromosomes attract each other and form bivalents.
Centrioles separate and start forming spindles.
Chromosomes shorten and thicken by coiling and then repel each other and move apart except at chiasmata. Here they have broken and joined to a different chromatid, Crossing over.
The nuclear membrane is still intact.

Question 18

2. METAPHASE

Answer 18

The nuclear membrane disappears, a spindle is formed and bivalents approach the equatorial region.

Question 19

3. ANAPHASE

Answer 19

The chromatids of the bivalents continue to separate and are pulled to opposite ends of the spindle by the spindle fibre contracting.

Question 20

4. SECOND MEIOTIC DIVISION

Answer 20

Two new spindles form at right angles to the first one and the chromatids of each pair separate and become chromosomes.

Question 21

5. TELOPHASE

Answer 21

The four groups of chromosomes are now enclosed in nuclear membranes, forming 4 nuclei containing the haploid number of chromosomes. The cytoplasm divides to separate the nuclei.

Question 21

Sources of variation

Answer 21

1. Crossing over – during Prophase 1
2. Independent assortment – random alignment of chromosomes at Metaphase I and again at
   Metaphase II
3. Random fertilization of gametes
4. Mutation