The Drosophila chromosome 4 is extremely small; there is virtually no recombination between genes on this chromosome. You have available three differently marked chromosome 4’s: one has a recessive...

The Drosophila chromosome 4 is extremely small; there is virtually no recombination between genes on this chromosome. You have available three differently marked chromosome 4’s: one has a recessive allele of the gene eyeless (
 ), causing very small eyes; one has a recessive allele of the cubitus interruptus (
 ) gene, which causes disruptions in the veins on the wings; and the third carries the recessive alleles of both genes. Drosophila adults can survive with two or three, but not with one or four, copies of chromosome 4.

a. How could you use these three chromosomes to find Drosophila mutants with defective meioses causing an elevated rate of nondisjunction?

b. Would your technique allow you to discriminate nondisjunction occurring during the first meiotic division from nondisjunction occurring during the second meiotic division?

c. What progeny would you expect if a fly recognizably formed from a gamete produced by nondisjunction were testcrossed to a fly homozygous for a chromosome 4 carrying both
 and
?

d. Geneticists have isolated so-called compound 4th chromosomes in which two entire
4’s are attached to the same centromere. How can such chromosomes be used to identify mutations causing increased meiotic nondisjunction? Are there any advantages relative to the method you described in part a?