All the offspring of a white hen and a black rooster are gray. The simplest explanation

The genetic makeup of an organism is called its __________, and the physical traits of an organism are called its __________.

Which of Mendels laws is represented by each statement? a. Alleles of each pair of homologous chromosomes separate independently during gamete formation. b. Alleles segregate during gamete formation; fertilization creates pairs of alleles once again.

Edward was found to be heterozygous (Ss) for the sickle-cell trait. The alleles represented by the letters S and s are a. on the X and Y chromosomes. b. linked. c. on homologous chromosomes. d. both present in each of Edwards sperm cells.

Whether an allele is dominant or recessive depends on a. how common the allele is, relative to other alleles. b. whether it is inherited from the mother or the father. c. whether it or another allele determines the phenotype when both are present. d. whether or not it is linked to other genes.

Two fruit flies with eyes of the usual red color are crossed, and their offspring are as follows: 77 red-eyed males, 71 ruby-eyed males, 152 redeyed females. The gene that controls whether eyes are red or ruby is __________, and the allele for ruby eyes is __________. a. autosomal (carried on an autosome); dominant b. autosomal; recessive c. sex-linked; dominant d. sex-linked; recessive

All the offspring of a white hen and a black rooster are gray. The simplest explanation for this pattern of inheritance is a. pleiotropy. b. sex linkage. c. codominance. d. incomplete dominance

A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes? (Hint: Review Figure 9.20.) a. A, B, or O b. AB only c. AB or O d. A, B, AB, or O

Duchenne muscular dystrophy is a sex-linked recessive disorder characterized by a progressive loss of muscle tissue. Neither Rudy nor Carla has Duchenne muscular dystrophy, but their first son does have it. If the couple has a second child, what is the probability that he or she will also have the disease?

Adult height in people is at least partially hereditary; tall parents tend to have tall children. But people come in a range of sizes, not just tall or short. What extension of Mendels model could produce this variation in height?

A purebred brown mouse is repeatedly mated with a purebred white mouse, and all their offspring are brown. If two of these brown offspring are mated, what fraction of the F2 mice will be brown?

How could you determine the genotype of one of the brown F2 mice in problem 10? How would you know whether a brown mouse is homozygous? Heterozygous?

Tim and Jan both have freckles (a dominant trait), but their son Michael does not. Show with a Punnett square how this is possible. If Tim and Jan have two more children, what is the probability that both of them will have freckles?

Incomplete dominance is seen in the inheritance of hypercholesterolemia. Mack and Toni are both heterozygous for this character, and both have elevated levels of cholesterol. Their daughter Katerina has a cholesterol level six times normal; she is apparently homozygous, hh. What fraction of Mack and Tonis children are likely to have elevated but not extreme levels of cholesterol, like their parents? If Mack and Toni have one more child, what is the probability that the child will suffer from the more serious form of hypercholesterolemia seen in Katerina?

Why was Henry VIII wrong to blame his wives for always producing daughters?

Both parents of a boy are phenotypically normal, but their son suffers from hemophilia, a sex-linked recessive disorder. Draw a pedigree that shows the genotypes of the three individuals. What fraction of the couples children are likely to suffer from hemophilia? What fraction are likely to be carriers?

Heather was surprised to discover that she suffered from red-green colorblindness. She told her biology professor, who said, Your father is colorblind, too, right? How did her professor know this? Why did her professor not say the same thing to the colorblind males in the class?

In rabbits, black hair depends on a dominant allele, B, and brown hair on a recessive allele, b. Short hair is due to a dominant allele, S, and long hair to a recessive allele, s. If a true-breeding black short-haired male is mated with a brown long-haired female, describe their offspring. What will be the genotypes of the offspring? If two of these F1 rabbits are mated, what phenotypes would you expect among their offspring? In what proportions?

In 1981, a stray cat with unusual curled-back ears was adopted by a family in Lakewood, California. Hundreds of descendants of this cat have since been born, and cat fanciers hope to develop the curl cat into a show breed. The curl allele is apparently dominant and carried on an autosome. Suppose you owned the first curl cat and wanted to develop a purebred variety. Describe tests that would determine whether the curl gene is dominant or recessive and whether it is autosomal or sex-linked.

Interpreting Data As shown in the Punnett square below, one variety of deafness is caused by an autosomal recessive allele. Two parents who do not show any signs of the disease but are carriers could therefore have a child who is deaf, because that child could inherit one recessive deafness-causing gene from each parent. Imagine that a deaf male mates with a hearing female. We know the deaf male must have the genotype dd, but the female could be either Dd or DD. Such a mating is essentially a testcross, like the one shown in Figure 9.10. If the parents first child has hearing, can you say with certainty what the mothers genotype must be? What if the couple has four children (none twins), all with hearingcan you say with certainty the mothers genotype? What would it take for a definitive genotype to be assigned?

There are now nearly 200 recognized breeds of dog, from the Affenpinscher to the Yorkshire Terrier. But several of these suffer from medical problems due to the inbreeding required to establish the breed. For example, nearly every Cavalier King Charles (discussed in the Biology and Society essay) suffers from heart murmurs caused by a genetically defective heart valve. Such problems are likely to remain as long as the organizations that oversee dog breeding maintain strict pedigree requirements. Some people are suggesting that every breed be allowed to mix with others to help introduce new gene lines free of the congenital defects. Why do you think the governing societies are resistant to such cross-breed mixing? What would you do if you were in charge of addressing the genetic defects that currently plague some breeds?

Gregor Mendel never saw a gene, yet he concluded that some inherited factors were responsible for the patterns of inheritance he observed in peas. Similarly, maps of Drosophila chromosomes (and the very idea that genes are carried on chromosomes) were conceived by observing the patterns of inheritance of linked genes, not by observing the genes directly. Is it legitimate for biologists to claim the existence of objects and processes they cannot actually see? How do scientists know whether an explanation is correct?

Many infertile couples turn to in vitro fertilization to try to have a baby. In this technique, sperm and ova are collected and used to create eight-cell embryos for implantation into a womans uterus. At the eight-cell stage, one of the fetal cells can be removed without causing harm to the developing fetus. Once removed, the cell can be genetically tested. Some couples may know that a particular genetic disease runs in their family. They might wish to avoid implanting any embryos with the disease-causing genes. Do you think this is an acceptable use of genetic testing? What if a couple wanted to use genetic testing to select embryos for traits unrelated to disease, such as freckles? Do you think that couples undergoing in vitro fertilization should be allowed to perform whatever genetic tests they wish? Or do you think that there should be limits on what tests can be performed? How do you draw the line between genetic tests that are acceptable and those that are not?