3. Mitosis & Meiosis

Question 1

What type of cells undergo mitotic cell division?

Answer 1

Somatic cells

Question 2

What is the product of mitosis?

Answer 2

2 identical daughter cells with exactly the same chromosomal content as the parent cell. Diploid cells with 23 pairs of chromosomes.

Question 3

Just before meiosis, what does the DNA look like in G2?

Answer 3

Chromosomes are replicated and sister chromatids are joined by a centromere. Not visible at this point as not condensed.

Question 4

What are the 5 stages of mitosis?

Answer 4

Prophase, Prometaphase, Metaphase, Anaphase & Telophase

Question 5

What happens in prophase which makes the DNA visible?

Answer 5

chromosomes condense

Question 6

At what stage do the spindle fibres attach to the centromeres?

Answer 6

Prometaphase

Question 7

What happens in metaphase?

Answer 7

The chromosomes line up along the metaphase plate

Question 8

In what phase does the nuclear envelope reappear in mitosis?

Answer 8

Telophase

Question 9

What differs during anaphase in mitosis and meiosis I?

Answer 9

In mitosis, the chromosomes are pulled apart and each chromatid is pulled to a different side of the cell.
During meiosis I, homologous chromosomes are separated. These are then separated into chromatids during meiosis II.

Question 10

What are telomeres and where are they located?

Answer 10

They are repeated sequences of DNA which are at each end of chromosome/chromatid. They protect DNA from degradation.

Question 11

What are the names for different position of the centromere, starting from central and working upwards.

Answer 11

Metacentric (central), submetacentric, acrocentric and telocentric (not in humans)

Question 12

During meiosis, when does crossing over/recombination occur?

Answer 12

Prophase I

Question 13

What is a bivalent or tetrad and when can it be seen?

Answer 13

It is when 2 replicated chromosomes, homologous pairs line up on the metaphase plate during metaphase I of meiosis.

Question 14

What are the 2 processes which lead to genetic variation in meiosis?

Answer 14

1. Random assortment of homologous pairs on metaphase plate.

2. Crossing over and exchanging of genetic information

Question 15

What is the product of meiosis?

Answer 15

4 non identical haploid (n) daughter cells

Question 16

How many chromosomes do the dividing cells have at the end of meiosis I?

Answer 16

Haploid (n) = 23 chromosomes

Question 17

How many chromosomes do the haploid daughter cells have after meiosis?

Answer 17

23 chromosomes (not paired)

Question 18

What is the difference in cell division in spermatogenesis and oogenesis?

Answer 18

Spermatogenesis produces 4 sperm (n) from 1 spermatocyte (2n) whereas oogenesis produces 1 egg (n) and 3 polar bodies from 1 oocyte (2n)

Question 19

What is a common cause of aneuploidy?

Answer 19

Non-disjunction of chromosomes during metaphase

Question 20

What will the be the result of non-disjunction at the first post-zygotes mitotic division?

Answer 20

46,N will divide to produce one monosomy cell line and one trisomy cell line. The monosomy cell line is usually lost.

Question 21

What is the result of non disjunction at later mitotic cell divisions?

Answer 21

46N will produce one monosomy cell line and one trisomy cell line. The monosomy will be lost and the trisomy will be combined with the normal cells. MOSAIC karyotype.

Question 22

What is mosaicism?

Answer 22

The presence of 2 or more cell lines in an individual

Question 23

What determines the degree of mosaicism?

Answer 23

When the non-disjunction takes place, later mitotic divisions will affect fewer cells.

Question 24

What will be the effect of non-disjunction in meiosis 1 ?

Answer 24

All offspring will have the wrong chromosome number. Half will be monosomy and half will be trisomy when fertilised.

Question 25

What happens if there is non-disjunction in meiosis II?

Answer 25

Half of the offspring will have the wrong chromosome number ( one trisomy and one monosomy) and have will be normal.

Question 26

What is a robertsonian translocation?

Answer 26

When 2 acrocentric chromosomes q arms fuse and p arms are lost, so the indictable will have 45 chromosomes.

Question 27

What gene is responsible for the initiation of male sex?

Answer 27

SRY gene on the Y chromosome

Question 28

23 unduplicated structures are seen to travel to each pole, what cell division is this?

Answer 28

Meiosis II.
Duplicated in meiosis I
46 in mitosis

Question 29

During mitosis, when does the Nucleolus disappear?

Answer 29

During prophase when the chromosomes are condensed and will only return when chromosomes decondense.

Question 30

What are the consequences of faulty meiosis ?

Answer 30

• infertility
• mental retardation
• miscarriage