Ap Bio ch 12 test your understanding

Assume you are mapping genes A, B, C, and D in Drosophila. You know that these genes are linked on the same chromosome, and you determine the recombination frequencies between each pair of genes to be as follows: A and B, 8%; A and C, 28%; A and D, 25%; B and C, 20%; B and D, 33%. Describe how you determined the recombination frequency for each pair of genes. Draw a chromosome map based on your data.

(a) For each pair of genes, had to generate an F1 dihybrid fly

A man with hemophilia (a recessive, sex-linked condition) has a daughter without the condition, who marries a man who does not have hemophilia. What is the probability that their daughter will have the condition? Their son? If they have four sons, that all will be affected?

0; ½; ¹/₁₆

Two genes of a flower, one controlling blue (B) versus white (b) petals and the other controlling round (R) versus oval (r) 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?

450 each of blue-oval and white-round and 50 each of blue-round and white-oval

A wild-type fruit fly (heterozygous for gray body color and red eyes) is mated with a black fruit fly with purple eyes. The offspring are wild-type, 721; black-purple, 751; gray-purple, 49; black-red, 45. What is the recombination frequency between these genes for body color and eye color? Using information from Figure 12.9, what fruit flies (genotypes and phenotypes) would you mate to determine the sequence of the body-color, wing-size, and eye-color genes on the chromosome?

6%; wild-type heterozygous for normal wings and red eyes × recessive homozygous for vestigial wings and purple eyes

You design Drosophila crosses to provide recombination data for gene a, which is located on the chromosome shown in Figure 12.12. Gene a has recombination frequencies of 14% with the vestigial-wing locus and 26% with the brown-eye locus. Approximately where is gene a located along the chromosome?

About one-third of distance from vestigial-wing locus to brown-eye locus

A space probe discovers a planet inhabited by creatures that reproduce with the same hereditary patterns seen in humans. Three phenotypic characters are height (T = tall, t = dwarf), head appendages (A = antennae, a = no antennae), and nose morphology (S = upturned snout, s = downturned snout). Since the creatures are not "intelligent," Earth scientists are able to do some controlled breeding experiments using various heterozygotes in testcrosses. For tall heterozygotes with antennae, the offspring are tall-antennae, 46; dwarf-antennae, 7; dwarf-no antennae, 42; tall-no antennae, 5. For heterozygotes with antennae and an upturned snout, the offspring are antennae-upturned snout, 47; antennae-downturned snout, 2; no antennae-downturned snout, 48; no antennae-upturned snout, 3. Calculate the recombination frequencies for both experiments.

Between T and A, 12%; between A and S, 5%

Using the information from problem 3, scientists do a further testcross using a heterozygote for height and nose morphology. The offspring are tall-upturned snout, 40; dwarf-upturned snout, 9; dwarf-downturned snout, 42; tall-downturned snout, 9. Calculate the recombination frequency from these data; then use your answer from problem 3 to determine the correct order of the three linked genes.

Between T and S, 18%; sequence of genes is T-A-S.

Assume that genes A and B are 50 map units apart on the same chromosome. An animal heterozygous at both loci is crossed with one that is homozygous recessive at both loci. What percentage of the offspring will show recombinant phenotypes? Without knowing that these genes are on the same chromosome, how would you interpret the results of this cross?

Fifty percent of offspring show phenotypes resulting from crossovers. results be same as those from cross where A and B were not on same chromosome, and you would interpret results to mean that genes are unlinked.

Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently unaffected parents and usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele? Is its inheritance sex-linked or autosomal? How do you know? Explain why this disorder is almost never seen in girls.

Recessive; if disorder were dominant, would affect one parent of a child born with disorder. disorder's inheritance is sex-linked because seen only in boys. For girl to have disorder, she would have to inherit recessive alleles from both parents. would be rare, since males with recessive allele on X chromosome die in their early teens.

A man with red-green color blindness (a recessive, sex-linked condition) marries a woman with normal vision whose father was color-blind. What is the probability that they will have a color-blind daughter? That their first son will be color-blind? (Note the different wording in the two questions.)

¼ for each daughter; ½ for first son