Concept explainers
The ability of humans to taste the bitter chemical phenylthiocarbamide (PTC) is a genetic trait. People with at least one copy of the normal, dominant allele of the PTC gene can taste PTC; those who are homozygous for a mutant, recessive allele cannot taste it. Could two parents able to taste PTC have a nontaster child? Could nontaster parents have a child able to taste PTC? A pair of taster parents, both of whom had one parent able to taste PTC and one nontaster parent, are expecting their first child. What is the chance that the child will be able to taste PTC? Unable to taste PTC? Suppose the first child is a nontaster. What is the chance that their second child will also be unable to taste PTC?
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Chapter 12 Solutions
Biology: The Dynamic Science (MindTap Course List)
- In humans, dark hair (D) is dominant over blondness (d), and color blindness (c) is a sex-linked recessive trait. A woman has a blond brother, a blond mother, and a dark-haired father. Her brother and her parents have normal vision. She bears the following three children by her blond, normal-visioned husband: a dark-haired son with normal vision, a dark-haired daughter with normal vision, and a dark-haired color blind son. What is the probability that her next (fourth) child will be a colorblind boy.arrow_forwardIn humans, dark hair (D) is dominant over blondness (d), and color blindness (c) is a sex-linked recessive trait. A woman has a blond brother, a blond mother, and a dark-haired father. Her brother and her parents have normal vision. She bears the following three children by her blond, normal-visioned husband: a dark-haired son with normal vision, a dark-haired daughter with normal vision, and a dark-haired color blind son. If he is a colorblind boy, what is the probability that he will have dark hair?arrow_forwardSickle cell anemia is a blood disorder that is expressed with incomplete dominance. The homozygous recessive phenotype has sickle shaped red blood cells that cause anemia and often death if untreated. If an unaffected father and mother move to the United States from Sub-Saharan Africa and several of their offspring have sickle cell anemia, what do we know about both parents' genotypes? One is homozygous recessive, the other is heterozygous They are both heterozygous They are both homozygous recessive One is homozygous dominant, the other is heterozygousarrow_forward
- 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 mother’s genotype must be? What if the couple has four children (none twins), all with hearing—can you say with certainty the mother’s genotype? What would it take for a definitive genotype to be assigned?arrow_forwardIn Humans, the ability to taste PTC is inherited as a dominant gene (T). In a marriage between 2 heterozygous tasters (Tt): (1) what is the probability of 3 taster children, (2) what is the probability of 3 taster girls, (3) Why is there a difference in the last two answers to this problem?arrow_forwardWith regard to the ABO blood types in humans, determine the genotypes of the individuals below: John: John is blood type A and his mom was type B Genotype = Jane: Jane is blood type B and her dad was type O Genotype John and Jane have kids. What are the possible blood types of their offspring, including the expected ratio of each? O John is A1", Jane is l'i, the blood type ratios of their children would be: 1 AB: 1A : 1B John is IA, Jane is l1", the blood type ratios of their children would be: 1 AB: 1 B John is 1Ai. Janc is iP1P, the blood typc ratios of their children would be: 1 AB: 1 A: 1B John is Jane is IPi, the blood type ratios of their children would be 1 AB : 1A 1B:10arrow_forward
- Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele have sharp spines, whereas homozygous recessive cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have long or short spines. Homozygous recessive cactuses have short spines. A cross between a homozygous sharp-long cactus and a dull short-spined cactus would produce what percentage of sharp-long cacti?arrow_forwardA common kind of red-green blindness in humans is caused by the presence of a sex-linked recessive gene c, whose normal allele is c+. Using these genes, what are the possible genotypes and their corresponding phenotypes in males and females? Can two colorblind parents produce a normal son? (b) A normal daughter? (c) Can two normal parents produce a colorblind son? (d) a colorblind daughter?arrow_forwardIn humans, the genetic disease cystic fibrosis is caused by a recessive allele (a). The normal (healthy) allele is dominant (A). What is the genotype of someone who has cystic fibrosis? What are the two different genotypes that a healthy person could have? If two people were both heterozygous for the cystic fibrosis gene, what fraction of their children would be likely to have this disease? Hint: Draw a Punnett square to figure it out.arrow_forward
- As seen in the photo, Labradors come in three colors-- black, brown and yellow. What is the genetic basis for these different coat colors? One gene produces melanin, a pigment which is deposited in the dog's fur and makes the color dark. With this gene, allele B (black) is dominant to allele b. Only in the case of a recessive homozygote (bb) will the dog's phenotype be brown. The regulatory gene is separate from the melanin gene but it acts as a switch, either turning the melanin gene on or turning it off. Allele E is dominant and allows for the melanin to be deposited in the dog's fur ("on" switch), but if the switch gene is a recessive homozygote, the melanin is blocked ("off" switch) and a yellow dog is the result! 1. Two other Labradors mate and produce puppies. Their genotypes are Bbee and BbEe. What color are each parent and what are the phenotypic rations of their offspring in the F1 Generation? Show your work with a Punnett square.arrow_forwardAs seen in the photo, Labradors come in three colors-- black, brown and yellow. What is the genetic basis for these different coat colors? One gene produces melanin, a pigment which is deposited in the dog's fur and makes the color dark. With this gene, allele B (black) is dominant to allele b. Only in the case of a recessive homozygote (bb) will the dog's phenotype be brown. The regulatory gene is separate from the melanin gene but it acts as a switch, either turning the melanin gene on or turning it off. Allele E is dominant and allows for the melanin to be deposited in the dog's fur ("on" switch), but if the switch gene is a recessive homozygote, the melanin is blocked ("off" switch) and a yellow dog is the result! Review the information on Labrador retrievers above. What are the phenotypic ratios of the F1 generation offspring of two dihybrids? Make sure to match the numbers with coat colors (e.g, which number in the ration goes with which color). Use a Punnett square to…arrow_forwardIn humans, color vision depends on genes encoding three pigments. The R (red pigment) and G (green pigment) genes are close together on the X chromosome, whereas the B (blue pigment) gene is autosomal. A recessive mutation in any one of these genes can cause color blindness. Suppose that a color-blind man married a woman with normal color vision. The four sons from this marriage were color-blind, and the five daughters were normal. Specify the most likely genotypes of both parents and their children, explaining your reasoning. (A pedigree drawing will probably be helpful.) (Problem 50 is by Rosemary Redfield.)arrow_forward
- Human Biology (MindTap Course List)BiologyISBN:9781305112100Author:Cecie Starr, Beverly McMillanPublisher:Cengage Learning