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.

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 sex-determining mechanism is of the XY1Y2: XX type. Thirteen chromosomes are present in the spermatogonia; 10 of these can be paired, while 3 (the X1Y1and 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; Y2is 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 Y2and 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