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Four basic genetics problems

Practice problems

1. You're working in a lab that studies a particularly gruesome parasite from the Amazon that infests people's ear canals while they sleep. This parasite has a diploid number of 12 chromosomes in its somatic cells, consisting of 6 homologous pairs (i.e. 6 maternal and 6 paternal chromosomes). Another student in your lab tells you that only one-fourth of the gametes produced by meiosis in this parasite will have all of it's chromosomes from either maternal or paternal origin (i.e. all the chromosomes from dad or all the chromosomes from mom). Assume that meiosis in this parasite works just like meiosis in organisms we've talked about in class and explain whether you think the student is correct.

2. A diploid somatic cell from a rat has a total of 42 chromosomes (2n = 42). Answer the following questions:
A. How many different chromosomes (i.e. carrying different genes) does the rat have?
B. How many molecules of DNA are in the nucleus of a somatic rat cell in G1?
C. How many telomeres are in the nucleus of a somatic rat cell in G1?
D. How many molecules of DNA are in the nucleus of a somatic rat cell in G2?
E. How many telomeres are in the nucleus of a somatic rat cell in G2?
F. How many DNA molecules are in the nucleus of a rat cell in metaphase of mitosis?
G. How many chromosomes are in the nucleus of a rat cell in metaphase of mitosis?
H. How many DNA molecules are in the nucleus of a rat cell in metaphase I of meiosis?
I. How many chromosomes are in the nucleus of a rat cell in metaphase I of meiosis?
J. How many DNA molecules are in the nucleus of a rat cell in metaphase II of meiosis?
K. How many chromosomes are in the nucleus of a rat cell in metaphase II of meiosis?

3. For a particular plant, red flowers (A) are dominant over yellow flowers (a). An initial cross was made between a plant that was true-breeding for red flowers, and another plant true-breeding for yellow flowers. F1 progeny, all having red flowers, were allowed to form seeds, which were then planted to generate F2 progeny. Pollen from all the resulting F2 plants was pooled and used to fertilize true-breeding yellow plants. What proportion of the progeny resulting from this cross would be expected to have yellow flowers?

4. You learn that a Mars lander has retrieved a bacterial sample from the polar ice caps. You obtain a sample of the bacteria and perform the same kind of experiment that Meselson and Stahl did to determine how the Mars bacteria replicates its DNA. Based on the following equilibrium centrifugation results, what type of replication would you propose for this new bacteria?

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