Potoroo Mitosis and Meiosis Worksheet, Fall 2012
Name:
Refer to the following pictures of female Rat Kangaroo (Potoroo) cells (2n=12)
during mitosis to answer the following questions. In these figures, mitochondria are
red, chromosomes are blue and microtubules are green.
A
B
C
D D
Question 1. Label each of the stages of mitosis above.
Question 2. How many chromatids are present in figure A?
Question 3. How many chromosomes are present in each of the nuclei in figure D?
Question 4. If these nuclei were in meiosis I, rather than mitosis, how many
chromatids would be present in figure A?
Question 5. If these nuclei were in meiosis II, rather than mitosis, how many
chromatids would be present in figure A?
Question 6. An abstract of a paper by Sharman, et al. (1950) reads as follows:
“A study of spermatogonial and ovarian mitosis and of meiosis in the potoroo
or rat kangaroo of Tasmania (Potorous tridactylus) indicates that the sexdetermining mechanism is of the XY1Y2: XX type. Thirteen chromosomes are
present in the spermatogonia; 10 of these can be paired, while 3 (the
X1 Y1 and Y2) have no partners. In ovarian mitoses 12 chromosomes are
present, all of which can easily be arranged in homologous pairs. The X
chromosomes are conspicuous by their long, nearly median centromere
constriction. Y1 is the smallest chromosome; Y2 is acrocentric. Five bivalents
and a trivalent (the X chromosome and a Y chromosome pairing with each
arm) are formed at the first meiotic division in the ♂ The 2 Ys always move
to one pole, the X to the opposite pole. Two types of sperm are produced, ♂determining (with 7 chromosomes), and ♀-determining (with 6
chromosomes). At the prophase the Y2 and its homologous arm in the X
behave similarly to the autosomes. Y1and the other arm of the X-chromosome
are strongly heterochromatic and are condensed into an irregular sphere at
earliest diplotene. It seems probable that the sex-determining mechanism
has arisen by translocation between the X-chromosome and an autosome,
with loss of a centromere. The existence of a multiple mechanism is indicated
also in the wallaby (Macropus ualabatus). The diploid number of
chromosomes in this species is 10 for the ♀ and 11 for the ♂ 3 of these 11
form a trivalent at meiosis. A trivalent at meiosis in the ♂ has also been
reported in the insectivore, Sorex wraneus. A. P. G.”
Sharman, GB, McIntosh, AJ and Barber, HN. 1950. Multiple sex
chromosomes in the marsupials. Nature 166: 996.
Draw how the sex chromosomes of male Potoroos would look during:
a) Metaphase of Mitosis
b) Metaphase of Meiosis I
c) Metaphase of Meiosis II
d) Anaphase of Mitosis
e) Anaphase of Meiosis I
f) Anaphase of Meiosis II