Solution-Determine a genetic map for these genes

1. The Drosophila genes scute, echinus and vestigial have as non-wild-type alleles sc (short for scute, or loss of certain thoracic bristles), ec (short for echinus, or roughened eye surface), and vg (short for vestigial wing). A wild-type true breeding fly is crossed with a triply recessive fly. The F1 females are testcrossed with tester males. The progeny are listed as gametic genotypes derived from the F1 females. Eight gametic types are possible, and they were counted in the following numbers in a sample of 1008 progeny flies:

sc · ec · vg                            235

sc+ · ec+ · vg+                      241

sc · ec · vg+                          243

sc+ · ec+ · vg                        233

sc · ec+ · vg                          12

sc+ · ec · vg+                        14

sc · ec+ · vg+                        14

sc+ · ec · vg                          16


A. Are the genes linked or unlinked? Explain your answer.

B. Determine a genetic map for these genes.

C. Based on the information you have gathered, how would you write the genotype of the parents of the testcross?

2. Mrs. Smith and Mrs. Doe were roommates at Harris Hospital and both had daughters at about the same time. After Mrs. Smith took Susie home, she became convinced that the babies had been switched.

Blood tests were performed with the following results:

Mr. and Mrs. Smith were both type AB;

Mr. and Mrs. Doe were both type A;

Susie Smith was type A and Debbie Doe was type O.

Had a switch occurred?

A. Determine the genotype of all the individuals involved.

B. Determine if a switch has occurred. Justify your answer discussing the children’s genotypes and using support from the parental genotypes.

3. In humans, sickle-cell anemia is caused by a recessive lethal allele Hbs; individuals who are HbaHbs have sickle-cell trait, but are healthy.

A. What is the probability of two heterozygous individuals giving birth to a child with sickle-cell trait?

B. What is the probability of two heterozygous individuals giving birth to a child with sickle-cell anemia?

C. If a normal HbaHba individual receives a blood transfusion from a HbaHbs individual (heterozygous for sickle cell) what are the chances that the HbaHba man and his HbaHba wife will have HbaHbs children?

4. Determine the mode of inheritance of the following trait:


Support your conclusion using references to specific individuals of the family.

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