Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.


What is the probability that the first child of Amanda and Brice will have galactosemia? Show your work.

Cross-1 shown in the following figure illustrates genetic complementation of flower-color mutants. The produced from this cross of two pure-breeding mutant parental plants are dihybrid (CcPp) and have wild-type flower color. If these F₁ are allowed to self-fertilize, what phenotypes are expected in the F₂ , and what are the expected ratios of the phenotypes?

Labrador retrievers may be black, brown (chocolate), or golden (yellow) in color (see chapter-opening photo). While each color may breed true, many different outcomes are seen when numerous litters are examined from a variety of matings where the parents are not necessarily true breeding. Following are just some of the many possibilities.

(a) black x brown → all black

(b) black x brown → 1/2 black, 1/2 brown

(c) black x brown → 3/4 black, 1/4 golden

(d) black x golden → all black

(e) black x golden → 4/8 golden 3/8 black 1/8 brown

(f) black x golden → 2/4 golden 1/4 black 1/4 brown

(g) brown x brown → 3/4 brown 1/4 golden

(h) black x black → 9/16 black 4/16 golden, 3/16 brown

Propose a mode of inheritance that is consistent with these data, and indicate the corresponding genotypes of the parents in each mating. Indicate as well the genotypes of dogs that breed true for each color.

The wild-type allele of a gene has an A–T base pair at a particular location in its sequence, and a mutant allele of the same gene has a G–C base pair at the same location. Otherwise, the sequences of the two alleles are identical. Does this information tell you anything about the dominance relationship of the alleles? Explain why or why not.

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.

If the first child has galactosemia, what is the probability that the second child will have galactosemia? Explain the reasoning for your answer.

Galactosemia is an autosomal recessive disorder caused by the inability to metabolize galactose, a component of the lactose found in mammalian milk. Galactosemia can be partially managed by eliminating dietary intake of lactose and galactose. Amanda is healthy, as are her parents, but her brother Alonzo has galactosemia. Brice has a similar family history. He and his parents are healthy, but his sister Brianna has galactosemia. Amanda and Brice are planning a family and seek genetic counseling. Based on the information provided, complete the following activities and answer the questions.

What is the probability that Amanda is a carrier of the allele for galactosemia? What is the probability that Brice is a carrier? Explain your reasoning for each answer.

A true-breeding purple-leafed plant isolated from one side of El Yunque, the rain forest in Puerto Rico, was crossed to a true-breeding white variety found on the other side. The F₁ offspring were all purple. A large number of F₁ x F₁ crosses produced the following results:

purple: 4219, white: 5781 (Total = 10,000)

Propose an explanation for the inheritance of leaf color. As a geneticist, how might you go about testing your hypothesis? Describe the genetic experiments that you would conduct.

In Dexter and Kerry cattle, animals may be polled (hornless) or horned. The Dexter animals have short legs, whereas the Kerry animals have long legs. When many offspring were obtained from matings between polled Kerrys and horned Dexters, half were found to be polled Dexters and half polled Kerrys. When these two types of F₁ cattle were mated to one another, the following F₂ data were obtained:

3/8 polled Dexters

3/8 polled Kerrys

1/8 horned Dexters

1/8 horned Kerrys

A geneticist was puzzled by these data and interviewed farmers who had bred these cattle for decades. She learned that Kerrys were true breeding. Dexters, on the other hand, were not true breeding and never produced as many offspring as Kerrys. Provide a genetic explanation for these observations.

A geneticist from an alien planet that prohibits genetic research brought with him to Earth two pure-breeding lines of frogs. One line croaks by uttering 'rib-it rib-it' and has purple eyes. The other line croaks more softly by muttering 'knee-deep knee-deep' and has green eyes. With a newfound freedom of inquiry, the geneticist mated the two types of frogs, producing F₁ frogs that were all utterers and had blue eyes. A large F₂ generation then yielded the following ratios:

27/64 blue-eyed, 'rib-it' utterer

12/64 green-eyed, 'rib-it' utterer

9/64 blue-eyed, 'knee-deep' mutterer

9/64 purple-eyed, 'rib-it' utterer

4/64 green-eyed, 'knee-deep' mutterer

3/64 purple-eyed, 'knee-deep' mutterer

In another experiment, the geneticist crossed two purple-eyed, 'rib-it' utterers together with the results shown here:

9/16 purple-eyed, 'rib-it' utterer

3/16 purple-eyed, 'knee-deep' mutterer

3/16 green-eyed, 'rib-it' utterer

1/16 green-eyed, 'knee-deep' mutterer

What were the genotypes of the two parents?