Meiosis

Question 1

What is meiosis?

Answer 1

The type of cell division that produces haploid (n) and genetically different cells called gametes. It is reduction division.

Meiosis is essential for sexual reproduction.

Question 2

Where does meiosis occur?

Answer 2

In the sex organs, specifically:
* testes and ovaries in mammals
* pollen grains and ovules in plants

Meiosis occurs in specialized cells that will develop into gametes.

Question 3

What occurs in the two rounds of cell division by meiosis?

Answer 3

Meiosis 1 separates the homologous chromosomes; Meiosis 2 separates sister chromatids.

This process results in four genetically unique haploid cells.

Question 4

When is the ploidy reduced from diploid to haploid?

Answer 4

During meiosis 1, hence it is known as the reduction division.

This reduction is crucial for maintaining the correct chromosome number across generations.

Question 5

What are bivalents and when are they formed?

Answer 5

Bivalents are the pairs of homologous chromosomes that form during interphase, just before prophase 1 starts.

Bivalents are essential for genetic recombination.

Question 6

What are the key events in prophase 1?

Answer 6

• Chromosomes condense and become visible
• Homologous chromosomes pair up to form bivalents
• Crossing over occurs between non-sister chromatids. The points where they cross over are called chiasmata
• The nucleus and nucleolus break down and disappear

Prophase 1 is critical for genetic diversity due to crossing over.

Question 7

What are the key events in metaphase 1?

Answer 7

Homologous pairs (tetrads) line up at the equator of the cell.
Spindle fibres attach to the centromere of each chromosome

This alignment is random and contributes to genetic variation through independent assortment.

Question 8

What happens during anaphase 1?

Answer 8

Spindle fibres contract to pull homologous chromosomes apart to opposite poles of the cell.

Question 9

What are the key events in telophase 1?

Answer 9

The chromosomes reach the opposite poles
Nuclear membrane reforms and cytokinesis occurs.

Question 10

Describe the cells formed at the end of telophase 1 of meiosis 1 after cytokinesis occurs describe the cells formed

Answer 10

Two haploid daughter cells are formed.
Their chromosomes consist of two chromatids joined by a centromere

Question 11

What are the key events in prophase 2?

Answer 11

Same as prophase 1
Chromosomes condense but homologous pairs do not form, centrioles duplicate and move to poles, nuclear membrane starts to break down.
Spindle fibres begin to form at right angles to the old spindle

Question 12

What happens during metaphase 2?

Answer 12

Spindle has now formed at right angles to the old one
Chromosomes align at the equator and attach to the spindle via their centromeres

Question 13

What occurs during anaphase 2?

Answer 13

Centromeres break and chromatids are pulled apart to opposite poles when the spindle fibres contract.

Question 14

What are the key events of telophase 2?

Answer 14

Chromosomes arrive at the poles, decondense, nuclear membrane reforms, and cytokinesis 2 occurs.

Question 15

Fill in the blank: During anaphase 1, spindle fibres contract to pull _______ chromosomes apart.

Answer 15

homologous

Question 16

True or False: At the end of telophase 1, the daughter cells are diploid.

Answer 16

False

Question 17

Fill in the blank: In prophase 2, spindle fibres begin to form at right angles to the _______.

Answer 17

old spindle

Question 18

What aligns at the equator during metaphase 2?

Answer 18

Chromosomes consisting of two chromatids.

Question 19

What will the end result be after cytokinesis in meiosis 2?

Answer 19

Four, haploid, genetically different daughter cells

Cytokinesis in meiosis 2 results in the formation of four unique gametes.

Question 20

When does genetic variation arise in meiosis?

Answer 20

During meiosis 1
Crossing over in prophase 1
Independent assortment in metaphase 1

Genetic variation arises due to processes such as crossing over and independent assortment.

Question 21

What is crossing over?

Answer 21

The non-sister chromatids of the bivalents entwine and swap sections at points called chiasmata.
Leads to a different combination of alleles in each chromosome

This process contributes to genetic diversity by creating new combinations of alleles.

Question 22

What is a chiasma?

Answer 22

A point where chromatids of a bivalent entwine and exchange sections of genes

Chiasmata are crucial for the process of crossing over.

Question 23

What is independent assortment?

Answer 23

The homologous pairs of chromosomes line up at the equator randomly at the start of metaphase 1
Which chromosome of each pair is closer to the poles is totally independent

This leads to the random distribution of chromosomes into gametes, increasing genetic variation.

Question 24

Fill in the blank: The two chromatids of each chromosome are no longer _______ after crossing over.

Answer 24

identical

This is a result of the genetic exchange that occurs during crossing over.

Question 25

What adds to the genetic variation of offspring resulting from sexual reproduction?

Answer 25

Random fusion and fertilisation of the gametes ## Footnote This process mixes genetic material from two parents, further increasing diversity.