Lecture 14: Eukaryotic Cell Division Meiosis

Question 1

What would happen if gametes were produced by mitosis?

Answer 1

If gametes were produced by mitosis, they would be
2n, and resulting embryos would be 4n.

Need a process of cell division that HALVES no. of chromosomes going into gametes (n), so that diploid number (2n) is retained in zygote.

Question 2

What is meiosis?

Answer 2

a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

Question 3

What does Meiosis I do?

Answer 3

Separates homologous chromsomes:

Prophase I
Mephase I
Anaphase I
Telophase I and cytokinesis

Question 4

What happens in prophase I?

Answer 4

Homologous
chromosomes align &
synapse

Crossing over between
non-sister chromatids
occurs at chiasmata

Crossing over results in
chromatids now being a
mix of pieces from each
homologous chromosome.

Question 5

What happens in Metaphase I?

Answer 5

Paired homologous
chromosomes move to
metaphase plate

Chiasmata (not
kinetochores, as in
mitosis) line up on
metaphase plate

Question 6

What happens in anaphase I?

Answer 6

Recombined homologous
chromosomes separate
(disjoin)

Sister chromatids remain
attached

In anaphase of mitosis, sister
chromatids separate

Question 7

Telophase I and cytoinesis

Answer 7

Haploid cells with
duplicated chromosomes
(the pairs of sister
chromatids) form

Haploid because only half
the genetic information is
in each new cell

Question 8

What happens in meiosis II?

Answer 8

Separates sister chromatids

Question 9

What happens during mitosis?

Answer 9

chromosomes
align independently

no chiasmata

centromeres on
metaphase plate

chromatids disjoin

2n - 2n

Question 10

What happens during meiosis I?

Answer 10

homologous
chromosomes synapse

chiasmata

chiasmata on
metaphase plate

chromosomes disjoin

2n - n

Question 11

If the sperm of a mouse has 3 picograms of DNA, the amount of DNA in the nucleus of a
somatic cell about to divide by mitosis would
be:

Answer 11

12 picograms

Question 12

The structures that move to the spindle poles at
anaphase of meiosis I usually differ from those
that move to the poles at anaphase II with
respect to:

A) chromatid number.

B) gene copy number.

C) the ratio of maternal to paternal genes.

D) all of the above.

Answer 12

D) all of the above

Question 13

how does sexual reproduction produce genetic diversity?

Answer 13

(i) independent assortment of chromosomes
(ii) crossing over and
(iii) random fertilization of gametes

Question 14

Genetic diversity allows selective responses what are some example?

Answer 14

(i) spatially variable environments
(e. g. climate, ecology)
(ii) changing environments
(e. g. parasites, seasons)
(i) sib-sib competition

Question 15

What is crossing over?

Answer 15

The exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.

In prophase I of meiosis the non sister chroatids are held together during synapsis

then movement to the metaphase 1 plate

breakdown of proteins holding sister chromatid arms together

Question 16

Drosophila males do not undergo crossing over
at meiosis. If Drosophila has a diploid number
of 8, how many genetically distinct types of
gametes can be produced by a male
Drosophila?
A) 4
B) 8
C) 16
D) 32

Answer 16

A) 4

Question 17

Presence of the sexual cycle in a species has
the potential to:
A) decrease competition among offspring.
B) allow the species to respond better to parasites.
C) increase evolutionary flexibility.
D) all of the above.

Answer 17

D) all of the above