11. Using the information from problem 10, scientists do a further testcross usin a
heterozygote for height and nose morphology. The offspring are: tall-upturned snount,
40: dwarf-upturnes snout, 9: dwarf-downturned snout, 42; tall-downturned snout, 9.
Calculate the recombination frequency from these data; then use your answer from
problem 10 to determine the correct sequence of the three linked genes.
- Between T and S: 18%
-The sequences if genes is T-A-S
12. The ABO blood type locus has been mapped on chromosome 9. A father who has
blood type AB and a mother who has blood type O have a child with trisomy 9 and blood
type A. Using this information, can you tell in which parent the nondisjunction occurred?
Explain your answer.
Father: IaIb
Ia i
Ia i
Ib i
Ib i
-The nondisjunction occurred was inherited form the mother because if it was the father
the child would have had AB blood type.
13. Two genes of a flower, one controlling blue (B) versus white (b) petals and the other
controlling round (R) versus oval ® stamens, are linked and are 10 map units apart. You
cross a homozygous blue-oval plant with a homozygous white-round plant. The resulting
F1 progeny are crossed with homozygous white-oval plants, and 1,000 F2 progeny are
obtained. How many F2 plants of each of the four phenotypes do you expect?
-There are 450 each of blue-oval and white round (parentals) and 50 each of blue-round
and white-oval (recombinants) for the F2 plants.
14. You design Drosophila crosses to provide recombination data for gene a, which is
located on the same chromosome shown in Figure 15.8. Gene a has recombination
frequencies of 14% with the vestigial-wing locus and 26% with the brown-eye locus.
Where is a located on the chromosome?
-The chromosome is located about 1/3 of the distance from the vestigial-wing locus to the
brown-eye locus.