Genetics Test 2

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an offspring with the AB phenotype from a cross of aabb × AABB?

1 (100%)

A couple has six daughters and is expecting a seventh child. What is the probability that this child will be a boy?

1/2

Freckles are caused by a dominant allele. A man has freckles but one of his parents does not have freckles. The man has fathered a child with a woman that does not have freckles. What is the probability that their child has freckles?

1/2

James is a 42-year-old man with hemophilia, a sex-linked recessive condition. His daughter, Susan, who has normal blood clotting, is married to Fred who also has hemophilia. Susan and Fred are expecting their first child and an ultrasound shows that the fetus is male. What is the approximate probability that their new son will have hemophilia?

1/2

If an AaBbccDd individual is crossed to an AaBbCcDD individual, what is the probability that the first offspring will be of AabbccDd genotype?

1/32

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AB gamete from an AaBb individual?

1/4

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AaBb zygote from a cross of AaBb × AABB?

1/4

A woman has normal vision although her maternal grandfather (her mother's father) had red-green color blindness, a sex-linked recessive trait. Her maternal grandmother and the woman's own father are assumed to not possess a copy of the mutant allele. The woman marries a man with normal vision although his father was color blind. What is the probability that the first child of this couple will be color blind?

1/8

Joan is phenotypically normal but had a child with the autosomal recessive disease cystic fibrosis (CF) from a previous marriage. Joan's father has hemophilia A, a sex-linked recessive condition where the blood fails to clot properly. Her father has survived due to recent treatment advances. Joan now intends to marry Bill, who is also phenotypically normal but who has a sister, Jill, with CF. Bill's parents are phenotypically normal, and there is no history of hemophilia A in his family. Assume that Joan and Bill do marry and have a child. What is the probability that this child will have CF but will not have hemophilia A? (Hint: This problem requires that you utilize concepts from Chapter 3 as well as Chapter 4.)

1/8

If both husband and wife are known to be heterozygous for the autosomal recessive condition of albinism, what is the probability that among their four children, three will be normal and one will have albinism?

27/64

A woman is phenotypically normal, but her father had the sex-linked recessive condition of red-green color blindness. If she has children with a man with normal vision, what is the probability that their first child will have normal vision and their second child will be color blind?

3/16

The very rare Bombay blood phenotype in humans (first discovered in Bombay, India) results in blood type O because of the lack of both the A and B antigens in individuals who are of hh genotype. This genotype results in blood type O regardless of the genotype at the unlinked I locus. If two parents are both of IA IB Hh genotype (type AB blood), what is the probability that their first child will also have type blood B?

3/16

In a cross between AaBbCcDdEe and AaBbccDdee, what proportion of the offspring would be expected to be A_bbC_ddE_? ( A_ means AA or Aa.)

3/256

In a cross between AABbCcDD and AaBbccdd, what proportion of the offspring would be expected to be A_B_C_D_? ( A_ means AA or Aa.)

3/8

In humans, occasionally a baby is found that has the XX chromosomal karyotype but is phenotypically male. Which of the following statements might be a CORRECT explanation for at least some of these unusual cases?

A piece of chromosomal material containing an active SRY gene is found attached to one of the X chromosomes.

A mother with blood type AB has a child with blood type B. Give all possible blood types for the father of this child

A, B, AB, O

A mother with blood type B has a child with blood type O. Give all possible blood types for the father of this child.

A, B, O

In humans, blood types A and B are codominant to each other and each is dominant to O. What blood types are possible among the offspring of a couple of blood types AB and A?

A, B, and AB only

A mother of blood type A gives birth to a child with blood type O. Which of the following could NOT be the blood type of the father?

AB

Which of the following crosses would produce a 3:1 ratio of phenotypes in the next generation?

Aa x Aa

Which of the following crosses would produce a 1:1 ratio of phenotypes in the next generation?

Aa x aa

Deafness is often inherited in humans as an autosomal recessive trait. Assume that this is the case here. Two severely deaf people meet and marry. They have four children and all of them have normal hearing. What is the MOST reasonable explanation for this outcome?

Complementation has occurred in the children, indicating that the deafness mutations in the parents involved different genes.

What is the apparent purpose for X inactivation in humans and other mammals?

It allows for the levels of expression of genes on the X chromosome to be similar in males and females.

What is the role of the SRY gene in humans

It is located on the Y chromosome and initiates the developmental pathway toward the male phenotype.

Round seeds ( R) are dominant to wrinkled seeds ( r), and yellow seeds ( Y) are dominant to green seeds ( y). A plant of unknown genotype is testcrossed to a true-breeding plant with wrinkled and green seeds. The offspring produced were 53 round and yellow, 49 round and green, 44 wrinkled and yellow, and 51 wrinkled and green. What is the likely genotype of the parent in question?

RrYy

Round seeds ( R) are dominant to wrinkled seeds ( r), and yellow seeds ( Y) are dominant to green seeds ( y). A true-breeding plant with round and yellow seeds is crossed to a true-breeding plant with wrinkled and green seeds. What is the genotype of the F 1 progeny?

RrYy

In Labrador retrievers, black coat color is dominant to brown. Suppose that a black Lab is mated with a brown one and the offspring are four black puppies and one brown puppy. What can you conclude about the genotype of the black parent?

The genotype must be Bb

A man is heterozygous for a rare trait that is assumed to be caused by a dominant autosomal mutant allele. He marries a woman who is phenotypically normal. They have a phenotypically normal daughter who marries a phenotypically normal man. Unexpectedly their first child, a girl, has the same abnormal trait as her grandfather. Which of the following BEST explains this situation?

The mutant allele shows reduced penetrance and the normal daughter carries the mutant allele.

Which of the following chromosome constitutions would never lead to a viable human baby being born?

YY

If an organism of genotype Aa was used for a testcross, what was the genotype of the other individual used in the cross?

aa

In dogs, black coat color ( B) is dominant over brown ( b), and solid coat color ( S) is dominant over white spotted coat ( s). A cross between a black, solid female and a black, solid male produces only puppies with black, solid coats. This same female was then mated with a brown, spotted male. Half of the offspring from this cross were black and solid, and half of the offspring were black and spotted. What is the genotype of the brown, spotted male?

bbss

The ability to curl one's tongue into a U-shape is a genetic trait. Curlers always have at least one curler parent but noncurlers can have one or both parents who are curlers. Using C and c to symbolize the alleles that control this trait, what is the genotype of a noncurler?

cc

Interactions among the human ABO blood group alleles involve _____ and _____.

codominance; complete dominance

Red-green color blindness is X-linked recessive. A woman with normal color vision has a father who is color blind. The woman has a child with a man with normal color vision. Which phenotype is NOT expected?

color-blind female

In a germ-line cell from a human male that is dividing, when do the X and Y chromosomes segregate?

during meiosis I, anaphase

Human males with XY chromosomes are _____ and produce two different kinds of gametes, whereas females with XX chromosomes are _____ and produce only one kind.

heterogametic; homogametic

Freckles are caused by a dominant allele. A man has freckles but one of his parents does not have freckles. What is the man's genotype?

heterozygous

A Barr body is a(n):

inactivated X chromosome, visible in the nucleus of a cell that is normally from a female mammal.

Suppose that extra fingers and toes are caused by a recessive trait, but it appears in only 60% of homozygous recessive individuals. Two heterozygotes conceive a child. What is the probability that this child will have extra fingers and toes?

o.15

Achondroplasia is a common cause of dwarfism in humans. All individuals with achondroplasia are thought to be heterozygous at the locus that controls this trait. When two individuals with achondroplasia mate, the offspring occur in a ratio of 2 achondroplasia : 1 normal. What is the MOST likely explanation for these observations?

the allele that causes achondroplasia is a dominant lethal allele

In poodles, black fur is dominant to white fur. A black poodle is crossed with a white poodle. In a litter of four, all of the puppies are black. What is the BEST conclusion?

the black poodle is probably homozygous

Two parents are phenotypically normal, but one of their four biological children has a typical autosomal recessive trait. The other three children are phenotypically normal. It is very likely that:

the parents are both heterozygous for the trait

Polydactyly is the condition of having extra fingers or toes. Some polydactylous persons possess extra fingers or toes that are fully functional, whereas others possess only a small tag of extra skin. This is an example of:

variable expressivity