Unpacking Problem 731. Define homozygous, mutation, allele, closely linked, recessive, wild type, crossing over, nondisjunction, testcross, phenotype, and genotype.2. Does this problem concern sex linkage? Explain.3. How many chromosomes does Drosophila have?4. Draw a clear pedigree summarizing the results of crosses1, 2, and 3.5. Draw the gametes produced by both parents in cross 1.6. Draw the chromosome 4 constitution of the progeny ofcross 1.7. Is it surprising that the progeny of cross 1 are wild-typephenotype? What does this outcome tell you?8. Draw the chromosome 4 constitution of the male testerused in cross 2 and the gametes that he can produce.9. With respect to chromosome 4, what gametes can thefemale parent in cross 2 produce in the absence of nondisjunction? Which would be common and which rare?10. Draw first- and second-division meiotic nondisjunctionin the female parent of cross 2, as well as in the resultinggametes.11. Are any of the gametes from part 10 aneuploid?12. Would you expect aneuploid gametes to give rise to viable progeny? Would these progeny be nullisomic, monosomic, disomic, or trisomic?13. What progeny phenotypes would be produced by thevarious gametes considered in parts 9 and 10?14. Consider the phenotypic ratio in the progeny of cross 3.Many genetic ratios are based on halves and quarters,but this ratio is based on thirds and sixths. To what mightthis ratio point?15. Could there be any significance to the fact that thecrosses concern genes on a very small chromosome?When is chromosome size relevant in genetics?16. Draw the progeny expected from cross 3 under the twohypotheses, and give some idea of relative proportions.
Unpacking Problem 73
1. Define homozygous, mutation, allele, closely linked, recessive, wild type, crossing over, nondisjunction, testcross, phenotype, and genotype.
2. Does this problem concern sex linkage? Explain.
3. How many chromosomes does Drosophila have?
4. Draw a clear pedigree summarizing the results of crosses
1, 2, and 3.
5. Draw the gametes produced by both parents in cross 1.
6. Draw the chromosome 4 constitution of the progeny of
cross 1.
7. Is it surprising that the progeny of cross 1 are wild-type
phenotype? What does this outcome tell you?
8. Draw the chromosome 4 constitution of the male tester
used in cross 2 and the gametes that he can produce.
9. With respect to chromosome 4, what gametes can the
female parent in cross 2 produce in the absence of nondisjunction? Which would be common and which rare?
10. Draw first- and second-division meiotic nondisjunction
in the female parent of cross 2, as well as in the resulting
gametes.
11. Are any of the gametes from part 10 aneuploid?
12. Would you expect aneuploid gametes to give rise to viable progeny? Would these progeny be nullisomic, monosomic, disomic, or trisomic?
13. What progeny
various gametes considered in parts 9 and 10?
14. Consider the phenotypic ratio in the progeny of cross 3.
Many genetic ratios are based on halves and quarters,
but this ratio is based on thirds and sixths. To what might
this ratio point?
15. Could there be any significance to the fact that the
crosses concern genes on a very small chromosome?
When is chromosome size relevant in genetics?
16. Draw the progeny expected from cross 3 under the two
hypotheses, and give some idea of relative proportions.
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