Crossing over, or recombination, is thought to be evolutionarily advantageous because it

A man with hemophilia (a recessive, sex-linked condition) has a normal daughter, who marries a normal man. What is the probability that a daughter will be a hemophiliac? A son? If the couple has four sons, that all will be affected?

Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently normal 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

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; dwarfno antennae, 42; tallno antennae, 5. For heterozygotes with antennae and an upturned snout, the offspring are antennae upturned snout, 47; antennaedownturned snout, 2; no antennaedownturned snout, 48; no antennaeupturned snout, 3. Calculate the recombination frequencies for both experiments.

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

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.)

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?

A wild-type fruit fly (heterozygous for gray body color and red eyes) is mated with a black fruit fly with purple eyes. The off- spring 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?

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?

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 whiteoval plants, and 1,000 F2 progeny are obtained. How many F2 plants of each of the four phenotypes do you expect?

Butterflies have an X-Y sex determination system that is different from that of flies or humans. Female butterflies may be either XY or XO, while butterflies with two or more X chromosomes are males. This photograph shows a tiger swallowtail gynandromorph, an individual that is half male (left side) and half female (right side). Given that the first division of the zygote divides the embryo into the future right and left halves of the butterfly, propose a hypothesis that explains how nondisjunction during the first mitosis might have produced this unusual-looking butterfly.

Crossing over, or recombination, is thought to be evolutionarily advantageous because it continually shuffles genetic alleles into novel combinations. Until recently, it was thought that Y-linked genes might degenerate because they have no homologous genes on the X chromosome with which to recombine. However, when the Y chromosome was sequenced, eight large regions were found to be internally homologous to each other, and quite a few of the 78 genes represent duplicates. How might this be beneficial?

The continuity of life is based on heritable information in the form of DNA. In a short essay (100150 words), relate the structure and behavior of chromosomes to inheritance in both asexually and sexually reproducing species.