1. What features make polytene chromosomes particularly useful for the detection of altered chromosomal structure?
2. Where other than a polytene chromosome could one look to verify the existence of a chromosomal inversion or partial duplication?
3. Define the following terms
A. Heterokaryon
B. Tandem duplication
C. Pseudodominance
D. Paracentric inversion
E. Reciprocal translocation
F. Translocation heterozygote
G. Unequal crossing over.
4. Deletions, duplications and inversions all cause the formation of loops in polytene chromosomes. How would you distinguish among these three possibilities cytologically? What genetic traits would you look for to support your conclusions?
5. Describe the mechanisms that lead to the production of Doublebar progeny from crosses of males that are hemizygous for Bar eye with females that are homozygous for Bar eye.
6. An inversion loop is more likely to cause severe problems during meiosis than a deletion loop. Explain the difference.
7. Under what conditions is a duplication of genetic material not abnormal?
8. Explain how a translocation can cause Down syndrome.
9. What special property distinguishes a deletion mutation from a typical missense point mutation (one that codes for the wrong amino acid)?
10. What mechanism has been proposed to account for the fact that humans have 46 chromosomes while the great apes have 48? What observations support the proposed mechanism?
11. Describe two distinctly different ways that Down syndrome can originate in humans (from two different lectures). What genetic similarity is shared in the two cases? How do they differ?
12. Explain how a deletion mutation can cause partial hemizygosity.
13. What is the molecular nature of a "fragile site" in a chromosome? What are the biological consequences of the fragile X syndrome.
14. What type of chromosomal change is particularly likely to result in a dominant phenotype with lethality in the homozygous state. What mechanism is likely to be involved in the lethality.
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