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Campbell Biology

Lisa A. Urry

Chapter 15

The Chromosomal Basis of Inheritance

Educators


Problem 1

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

Bryan L.
Numerade Educator

Problem 2

Knowledge/Comprehension
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.

Bryan L.
Numerade Educator

Problem 3

Knowledge/Comprehension
A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wildtype, 778; black vestigial, 785; black normal, 158; gray vestigial, 162. What is the recombination frequency between these genes for body color and wing size? Is this consistent with the results of the experiment in Figure 15.9?

Bryan L.
Numerade Educator

Problem 4

Knowledge/Comprehension
A planet is 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.

Bryan L.
Numerade Educator

Problem 5

Application/Analysis
Using the information from problem 4, 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, and then use your answer from problem 4 to determine the correct order of the three linked genes

Bryan L.
Numerade Educator

Problem 6

Application/Analysis
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 problem 3, what fruit flies (genotypes and phenotypes) would you mate to determine the order of the body color, wing size, and eye color genes on the chromosome?

Bryan L.
Numerade Educator

Problem 7

Application/Analysis
Assume that genes A and B are on the same chromosome and are 50 map units apart. 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 resulting from crossovers? Without knowing these genes are on the same chromosome, how would you interpret the results of this cross?

Bryan L.
Numerade Educator

Problem 8

Application/Analysis
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 homozyous blue oval plant with a homozygous white round plant. The resulting $\mathrm{F}_{1}$ progeny are crossed with homozyous white oval plants, and 1,000 offspring plants are obtained. How many plants of each of the four phenotypes do you expect?

Bryan L.
Numerade Educator

Problem 9

Application/Analysis
You design Drosophila crosses to provide recombination data for gene $a,$ which is located on the chromosome shown in Figure 15.12. Gene a has recombination frequencies of 14$\%$ with the vestigial wing locus and 26$\%$ with the brown eye locus. Approximately where is a located along the chromosome?

Bryan L.
Numerade Educator

Problem 10

Synthesis/Evaluation Banana plants, which are triploid, are seedless and therefore sterile. Propose a possible explanation

Bryan L.
Numerade Educator

Problem 11

Synthesis/Evaluation
EVOLUTION CONNECTION Crossing over is thought to be evolutionarily advantageous because it continually shuffles genetic alleles into novel combinations. Until recently, it was thought that the genes on the Y chromosome might degenerate because they lack homologous genes on the X chromosome with which to pair up prior to crossing over. 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. (Y chromosome researcher David Page has called it a "hall of mirrors.") Explain what might be a benefit of these regions.

Bryan L.
Numerade Educator

Problem 12

Synthesis/Evaluation
SCIENTIFIC INQUIRY $\bullet$ DRAW IT 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: $A-B, 8 \% ; A-C, 28 \% ; A-D, 25 \% ; B-C, 20 \% ; B-D, 33 \% .$
(a) Describe how you determined the recombination frequency for each pair of genes.
(b) Draw a chromosome map based on your data.

Michelle K.
Numerade Educator

Problem 13

Synthesis/Evaluation
WRITE ABOUT A THEME: INFORMATION The continuity of life is based on heritable information in the form of DNA. In a short essay (100-150 words), relate the structure and behavior of chromosomes to inheritance in both asexually and sexually reproducing species.

Bryan L.
Numerade Educator

Problem 14

Synthesis/Evaluation
SYNTHESIZE YOUR KNOWLEDGE Butterflies have an X -Y sex determination system that is different from that of flies or humans. Female butterflies may be butterflies with two or more X chromosomes are males. This photograph shows a tiger swallowtail gynandromorph, which 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 nondisunction during the first mitosis might have produced this unusual-looking butterfly.

Bryan L.
Numerade Educator