GTS 161 - PRACTICAL 1 – 2014
ADDITIONAL QUESTIONS
1.
In this problem you will be drawing a number of diagrams that illustrate your
understanding of cell division.
For all drawings assume the organism has 2n = 6, therefore 3 pairs of homologous
chromosomes.
Chromosome 1 is large and submetacentric, and carries gene A on the q-arm (long
arm).
Chromosome 2 is medium sized and metacentric, and carries the B locus.
Chromosome 3 is smaller and submetacentric, and carries gene G on the p-arm
(short arm).
NB : In all drawings, show the alleles of the loci on EACH chromatid.
Mitosis:
a. Make a schematic representation of the chromosomes of a non-dividing somatic cell
of this organism (G0 of interphase). Assume the individual is heterozygous for all
three loci (AaBbGg). Use a solid line for a chromatid.
b. Draw a new cell showing the arrangement of these chromosomes on the equatorial
plate during mitotic metaphase. How many chromatids should there now be per
chromosome? Why? Indicate the alleles of the loci on each chromatid.
c. Draw this cell in mitotic anaphase.
d. How many chromosomes will be present in each daughter cell at telophase? How
many alleles of each locus will be present in each daughter cell?
Meiosis:
e. Draw a cell showing one possible arrangement of the three bivalents on the
equatorial plate during metaphase I of meiosis (do not consider cross-overs). How
many chromatids should there be per chromosome? Why?
f. Draw a different metaphase I cell, with another possible arrangement of the
homologous pairs, that will allow you illustrate independent assortment when you
compare the cell in (f) to that in (e).
g. Theoretically, how many different gametes can be produced from independent
assortment for this organism with 2n = 6?
h. Draw the telophase I products that will arise from the cell in (e).
i.
Did the homologous chromosomes separate from one another during meiosis I? Did
sister chromatids separate from each other during meiosis I?
j.
Consider one of the telophase I products in (h). Now make a new drawing, showing
the arrangement of the chromosomes in this cell on the equatorial plate during
metaphase II of meiosis. Indicate the alleles.
k. Draw the telophase II products that will arise from the cell in (j).
l.
Did the alleles separate from one another, i.e. did sister chromatid segregation take
place, during meiosis II?
m. Why is it necessary for meiosis to consist of two divisions?
2.
The following represents a cell in Metaphase I, for an organism with 2n=4 that is
heterozygous for both the R and H loci. Dashed lines represent maternal
chromosomes and solid lines paternal chromosomes. In each bivalent a single
cross-over has occurred at the position and involving the chromatids as indicated.
1
H
A
r
aa
h
R
Draw this cell as it would appear in each of the cases listed below. Remember to
always indicate the nature of the chromatids (dashed for maternal / solid for
paternal), as well as the allele carried on each chromatid.
a.
b.
c.
Anaphase I.
The two Metaphase II cells.
The four resulting gametes.
TEXTBOOK QUESTIONS
Chapter 2 p 42-44 (4th Ed p 39-40)
Comprehension Questions 3, 12, 14, 15 (Not present in 4th Ed)
3. List three fundamental events that must take place in cell reproduction.
12. Why are the two cells produced by the cell cycle genetically identical?
14. What are the major results of meiosis?
15. What two processes unique to meiosis are responsible for genetic variation? At what
point in meiosis do these processes take place?
Application Questions and Problems 26, 27, 33, 38 (4th Ed Q’s 4, 5, 11, 15)
26. A cell in G1 of interphase has 12 chromosomes. How many chromosomes and DNA
molecules will be found per cell when this original cell progresses to the following
stages?
a. G2 of interphase
b. Metaphase I of meiosis
c. Prophase of mitosis
d. Anaphase I of meiosis
e. Anaphase II of meiosis
f. Prophase II of meiosis
g. After cytokinesis following mitosis
h. After cytokinesis following meiosis II
27. How are the events that take place in spermatogenesis and oogenesis similar? How
are they different?
33. The fruit fly Drosophila melanogaster has four pairs of chromosomes, whereas the
house fly Musca domestica has six pairs of chromosomes. All things being equal, in
which species would you expect to see more genetic variation among the progeny of
a cross? Explain your answer.
38. A primary oocyte divides to give rise to a secondary oocyte and a first polar body.
The secondary oocyte then divides to give rise to an ovum and a second polar body.
a. Is the genetic information found in the first polar body identical with that found
in the secondary oocyte? Explain your answer.
b. Is the genetic information found in the second polar body identical with that in
the ovum? Explain your reasoning.
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