Intellectual Genesis

Some important calculation in molecular biology.

1. In a particular family, one parent has Type A blood, the other has Type B. They have four children. One has Type A, one has Type B, one has Type AB, and the last has Type O. What are the genotypes of all six people in this family?

NOTE: The ABO blood type gene has three alleles. IA and IB are codominant; i (for Type O) is recessive to both.

2. Refer to problem I.3. Mrs. Smith has blood type A. Mr. Smith has blood type B. Their first child has blood type AB. Their second child has blood type O. Now is Mr. Smith justified? What are Mr. and Mrs. Smith’s genotypes for these two genes?

3. In a recent case in Spokane, Washington, a young woman accused a soldier of being the father of her child. The soldier, of course, denied it. The soldier’s lawyer demanded that blood types be taken to prove the innocence of his client. The following results were obtained: Alleged father, Type O. Mother, Type A. Child, Type AB. The court found the soldier guilty on the basis of the woman’s remarkable memory for dates and details that apparently eliminated all other possible fathers. a. What are the possible genotypes for these three people? b. Do you agree with the court’s decision? Why or why not?

1. Plutonian Tickle-bellies have a s*x determination system just like mammals. Hairy Snout is a holandric trait (carried on the Y chromosome). MyxRotcccc, a handsome male Tickle-belly, has lovely orange hair on his snout. He and his mate, OrgggWny, have six offspring, three boys and three girls. Please answer the following questions about this family. a. How many of MyxRotcccc’s and OrgggWny’s offspring have hairy snouts? Can you predict which ones? b. Their eldest son, Bob, marries and has a son. What is the chance that Bob’s son will also have a hairy snout? c. JoKchew, MyxRotcccc’s and OrgggWny’s youngest daughter, marries a male who has a smooth, hairless purple snout. She has eight offspring, each one lovelier than the last, and all boys. What percentage of these offspring do you expect to have hairy snouts? Explain.

2. In fruit flies (Drosophila), one eye color gene is X-linked, with a recessive white allele and a dominant red allele. If white-eyed female flies are bred to red-eyed male flies, describe the expected offspring (assume all parental flies are true-breeding). What results do you expect if you do the reciprocal cross (reverse the phenotypes of the parent flies)?

3. Earl has normal color vision, while his wife Erma is colorblind. . Colorblindness is an X-linked trait, and the normal allele is dominant to the colorblindness allele. If they have a large family, in what ways should the colorblindness trait affect their children?

4. Ethan is colorblind. His wife, Edna, is homozygous for the normal color vision allele. If they have eight children, how man of them would you expect to be colorblind? Using Punnett’s squares, derive and compare the genotypic and phenotypic ratios expected for the offspring of this marriage and those expected for the offspring of the marriage described in III.3.

5. Marian’s father is colorblind, as is her maternal grandfather (her mother’s father). Marian herself has normal color vision. Marian and her husband, Martin, who is also colorblind, have just had their first child, a son they have named Mickey. Please answer the following questions about this small family. a. What is the probability that this child will be colorblind? b. Three sources of the colorblindness allele are mentioned in this family. If Mickey is colorblind, from which of these three men (Marian’s grandfather, Marian’s father, or Martin) did he inherit the allele?
c. Using proper pedigree format, diagram the available information about the four generations of this family described, assuming that Mickey is colorblind. d. If Martin were not colorblind, how would this affect the prediction about Mickey?

6. In cats, there is a coat color gene located on the X chromosome. This gene is a different gene from the black/Siamese gene discussed in earlier problems. This gene has two alleles—orange and black. A heterozygous cat has tortoiseshell color (a splotchy mixture of orange and black). Predict the genotypic and phenotypic frequencies among the offspring of the following crosses. Pay careful attention to the genders of the offspring. a. Black female X Orange male b. Orange female X Black male c. Tortoiseshell female X Black male d. Tortoiseshell female X Orange male

1. A man with dark (dominant), curly (see problem I.5.) hair marries a woman with light, straight hair. Their daughter, who happens to have dark hair, marries a man with light, wavy hair. Answer the following questions about this dark-haired daughter and her family. a. Draw a Punnett’s square for this marriage, and predict the phenotypic ratio among the offspring of the daughter and her husband. b. What is the chance that they will have a child with hair just like his or her father’s?

2. In cats, again, black color is dominant to a special, temperature-sensitive albino gene which produces cats with dark legs, faces and tails (Siamese cats, in case you don’t recognize it). A short haired (dominant) Siamese colored female is bred to a long-haired black male. They have eight kittens: 2 black, short-haired; 2 black, long-haired; 2 Siamese, short-haired; and 2 Siamese, long-haired. What were the genotypes of the two parents?

3. Elizabeth is married to John, and they have four children. Elizabeth has a straight nose (recessive) and is able to roll her tongue (dominant). John is also able to roll his tongue, but he has a convex (Roman) nose (dominant). Of their four children, Ellen is just like her father, and Dan is just like his mother. The other children—Anne, who has a convex nose, and Peter, who has a straight nose—are unable to roll their tongues. Please answer the following questions about this family. a. What are the genotypes of Elizabeth and John? b. Elizabeth’s father was a straight-nosed roller, while her mother was a convex-nosed non-roller. What can you figure out about their genotypes? c. John’s father was a straight-nosed roller, while his mother was a convex-nosed roller. What can you determine about their genotypes? d. Diagram the three described generations of this family in accepted pedigree form, including the phenotypes for these two traits.

4. If a pure-breeding (homozygous) black (dominant), long-haired (recessive) cat is mated to a purebreeding Siamese, short-haired cat, and one of their male offspring is mated to one of their female offspring, what is the chance of producing a Siamese colored, short-haired kitten?

5. In horses, one which runs best in water (or in wet conditions) is called (WATER), and one which runs best in dry conditions is called (DRY). (WATER) is recessive to (DRY). A horse can also be either a trotter, which we will designate (GAIT) or a pacer, which we will designate (PACE). (PACE) is recessive to (GATE). We have mated two horses, a stallion named Halter-Man and a mare named Erlich-Mane. Halter-Man is a (WATER)(PACER), while Erlich-mane is a (DRY)(GAIT). One of Erlich-Mane’s parents was a (WATER)(PACER). What are the chances of Erlich-Mane and Halter-Man producing a (WATER)(GAIT) foal (that’s a baby horse, in case you didn’t know)?

6. When a male pig from a line of true-breeding (homozygous) black, solid-hooved pigs was crossed to a female from a breed (homozygous) of red, cloven-hooved pigs, their several progeny all looked alike with regard to color and hooves. These progeny were all mated to members of the same breed as their red, cloven-hooved mother pig. The offspring from this final cross were: 11 black, cloven-hooved; 8 black, solid-hooved; 14 red, cloven-hooved; and 10 red, solid-hooved. For each of these two genes (coat color and hoof type) determine which allele is the dominant one. Explain your reasoning. What were the phenotypes of the progeny produced by the first mating in this problem?

7. In garden peas, long stems are dominant to short stems, and yellow seeds are dominant to green seeds. 100 long/yellow pea plants, all of which had one short/green parent, are interbred (bred to each other). 1600 progeny result. Please answer the following questions about these progeny. a. Assuming that these two genes are unlinked, about how many long/green pea plants would you expect to find among the offspring? b. What ratio of yellow to green seed color would you expect among the offspring? c. What would you expect the overall phenotypic ratio among the 1600 offspring to be (taking into consideration both traits)?

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