BLec Ch. 9

If one parent is blood type AB and the other is type O, what fraction of their offspring will be blood type A? a) 0.5 b) 0.75 c) 1.0 d) O

a) 0.5 : About half the offspring would be expected to inherit the A allele and be phenotypically A.

Michelle and Keith are apparently normal, but their daughter was born with alkaptonuria, an inherited metabolic disorder that causes urine to turn black when exposed to air. If alkaptonuria is like most other human hereditary disorders, the probability of their next child being born with alkaptonuria is _____. a) 25% b) 0% c) 50% d) 100%

a) 25%. The chances of their next child having alkaptonuria are always 1:4 because they must both be carriers (Aa) for their daughter to have it.

A testcross is... a) a mating between an individual of unknown genotype and an individual homozygous recessive for the trait of interest. b) a mating between two individuals heterozygous for the trait of interest. c) a mating between an individual of unknown genotype and an individual heterozygous for the trait of interest. d) a mating between two individuals of unknown genotype.

a) a mating between an individual of unknown genotype and an individual homozygous recessive for the trait of interest.

Most genetic disorders of humans are caused by ... a) multiple alleles. b) recessive alleles. c) dominant alleles. d) a mutation that occurs in the egg, sperm, or zygote

a) recessive alleles

Hemophilia appears rarely in females. This is because _____. a) the female must possess the hemophilia gene on both X chromosomes b) it only affects males because they only have one X chromosome c) it only affects females with two X chromosomes d) the female must possess the hemophilia gene on one X chromosome

a) the female must possess the hemophilia gene on both X chromosomes: Because hemophilia is an X-linked recessive disorder, the female must have the gene on both X chromosomes. For this to occur, one parent must have hemophilia and one must be a carrier.

Hypercholesterolemia is a disorder in which blood cholesterol levels are elevated. The H allele is incompletely dominant to the h allele, with hh homozygotes having extremely high levels of blood cholesterol. A husband and wife are both Hh heterozygotes. What is the chance that their first child will have normal levels of blood cholesterol? a) 0 b) 1/4 c) 1/2 d) 3/4

b) 1/4 : This is the probability of giving birth to an HH homozygote, the only genotype conferring normal cholesterol levels.

In lentils, the C gene has two different alleles. CS CS homozygotes have spotted seeds, CD CD homozygotes have dotted seeds, and CS CD heterozygotes have seeds with both spots and dots. This indicates that _____. a) CD is completely dominant to CS b) CS and CD are codominant c) CS is completely dominant to CD d) CS and CD are incompletely dominant

b) CS and CD are codominant

Two individuals decide to have children. The expected blood group genotypes are 50% of blood type A, and 25% each of blood types AB and B. What genotypes are the parents? a) IA i x IB i b) IA i x IA IB c) IA i x ii d) IB i x IA IB

b) IAi x IAIB. Since blood groups show codominance, the child of blood type A must be either IA IA or IA i. This is also true of the child with blood type B. However, because there are more offspring expected with blood type A, we know that an A allele is being contributed from both parents. By reversing the Punnett square, the parents' genotypes are observed to be IA i and IA IB .

All the offspring of a cross between a red-flowered plant and a white-flowered plant have pink flowers. This means that the allele for red flowers is ________ to the allele for white flowers. a) dominant b) incompletely dominant c) recessive d) codominant

b) incompletely dominant

Imagine that we mate two black Labrador dogs with normal vision and find that three of the puppies are like the parents, but one puppy is chocolate with normal vision and another is black with PRA (progressive retinal atrophy, a serious disease of vision). We can conclude that... a) the alleles for color and vision segregate dependently during gamete formation. b) the alleles for color and vision segregate independently during gamete formation. c) the same alleles that control coat color can also cause PRA. d) both of the parents are homozygous for both traits.

b) the alleles for color and vision segregate independently during gamete formation.

Vitamin D - resistant rickets is an X-linked dominant bone disorder. A man with this form of rickets marries a normal woman. What proportion of the couple's daughters is expected to have vitamin D - resistant rickets? a. 25% b. 100% c. 0% d. 50%

b. 100% : Because daughters receive one of their X chromosomes from their father, and this chromosome contains the dominant allele, all daughters will be affected.

A person with AB blood illustrates the principle of a. polygenic inheritance. b. codominance. c. pleiotropy. d. incomplete dominance.

b. codominance.

If hair color, eye color, and the presence or absence of freckles were consistently inherited together, the best explanation would be that _____. a. gene duplications have occurred b. the genes for these characters are linked on the same chromosome c. these traits are recessive characteristics d. both parents have the same hair color, eye color, and freckles

b. the genes for these characters are linked on the same chromosome: Genes located on the same chromosome are inherited together and are said to be linked

Assume that in cattle a spotted coat is dominant to an even coat, short horns are dominant to long horns, and the traits for coat type and horn length assort independently. In a cross between cattle that are each heterozygous for both traits, what proportion of their offspring are expected to have long horns? a) 1/16 b) 3/16 c) 1/4 d) 9/16

c) 1/4. Because these traits assort independently, this dihybrid cross can be considered as two separate monohybrid crosses, with the consequence that one-fourth of the offspring of cattle heterozygous for the horn length trait will express the recessive long-horn trait.

A woman with type O blood is expecting a child. Her husband is type A. Both the woman's father and her husband's father had type B blood. What is the probability that the child will have type O blood? a) 75% b) 25% c) 50% d) 100%

c) 50% : The woman must beii. The husband is A but must be a carrier of the i allele, as his father was B. (The father did not give him a B allele, or the husband would be AB, so he must have given him a recessive i allele.) The cross ii x IA i yields a 50% probability that the child will be ii, or type O.

Recessive X-linked traits are more likely to be expressed in a male fruit fly than a female fruit fly because a) the male chromosome is more susceptible to mutations. b) males are haploid. c) the male's phenotype results entirely from his single X-linked gene. d) the male chromosome is more fragile than the female chromosome.

c) the males phenotype results entirely from his single X-linked gene

A woman who is a carrier of hemophilia marries a man affected with hemophilia. What percentage of their sons and daughters is expected to have hemophilia? a. 100% of sons and 50% of daughters b. 0% of sons and 50% of daughters c. 50% of sons and 50% of daughters d. 50% of sons and 0% of daughters

c. 50% of sons and 50% of daughters: Because sons obtain their single X chromosome from their mother, they have a 50% chance of inheriting the homolog that carries the hemophilia allele. And because daughters inherit their father's only X chromosome and one of the two X chromosomes of their mother, in this cross they have a 50% chance of being homozygous for the hemophilia allele.

A red bull is crossed with a white cow and all of the offspring are roan, a shade between red and white. This is an example of genes that are _____. a. nonhomologous b. codominant c. incompletely dominant d. an interaction between other alleles

c. incompletely dominant: In incomplete dominance, the offspring have phenotypes somewhere between the phenotypes of the two parental varieties.

Sex-linked conditions are more common in men than in women because a. the genes associated with the sex-linked conditions are linked to the Y chromosome, which determines maleness. b. men acquire two copies of the defective gene during fertilization. c. men need to inherit only one copy of the recessive allele for the condition to be fully expressed. d. the sex chromosomes are more active in men than in women.

c. men need to inherit only one copy of the recessive allele for the condition to be fully expressed

If A is dominant to a and B is dominant to b, what is the expected phenotypic ratio of the cross: AaBb × AaBb? a) 8:4:2:2 b) 1:1:1:1 c) 16:0:0:0 d) 9:3:3:1

d) 9:3:3:1

Imagine that beak color in a finch species is controlled by a single gene. You mate a finch homozygous for orange (pigmented) beak with a finch homozygous for ivory (unpigmented) beak and get numerous offspring, all of which have a pale, ivory-orange beak. This pattern of color expression is most likely to be an example of a) codominance. b) polygenic inheritance. c) pleiotropy. d) incomplete dominance.

d) incomplete dominance

There are over 100 alleles known for the gene associated with cystic fibrosis. With current technology, it is possible to determine exactly which allele or alleles is/are carried by a person. What is the maximum number of different alleles that any person can carry? a.16 b. 1 c. as many as there are alleles of the gene (~100 in this case) d. 2

d. 2 :Because there are two chromosomes, each with one locus for this and every other gene, a person may carry up to two different alleles for this gene.