Chapter 14 questions

A genetic counselor is working with a couple who have just had a child who has Tay-Sachs disease. Neither parent has Tay-Sachs, nor does anyone in their families. What should the counselor say to this couple?

"Because you have had one child with Tay-Sachs, you must each carry the allele. Any child you have has a 25% chance of having the disease."

Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr × PpRr will have white flowers and wrinkled seeds?

1/16

If a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous?

1/2

An individual with the genotype AaBbEeHH is crossed with an individual who is aaBbEehh. What is the likelihood of having offspring with the genotype AabbEEHh?

1/32

Michelle and Keith are apparently healthy, but their daughter was born with alkaptonuria, an inherited metabolic disorder. If alkaptonuria is like most other human hereditary disorders, the probability of their next child being born with alkaptonuria is __________.

1/4

An AABbccDdEeFF individual is crossed with an individual with the genotype AaBBCCDdEeff. What is the probability that their offspring will have the genotype AaBBCcddEEFf?

1/64

If each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce?

10,000

Roan cattle result from incomplete dominance of red and white alleles at a single locus. If two roan cattle are allowed to breed, what ratio of phenotypes is expected in the offspring?

1:2:1 red:roan:white

Tom's brother suffers from phenylketonuria (PKU), a recessive disorder. Tom and the brothers' parents do not have PKU. What are the chances that Tom is a carrier of the recessive PKU allele?

2/3

John, age 47, has just been diagnosed with Huntington's disease, which is caused by a rare dominant allele. His daughter, age 25, has a 2-year-old son. No one else in the family has the disease. Without knowing anything about the 25-year-old daughter's genotype, what is the probability that the 2-year-old son will eventually develop the disease?

25%

Imagine a locus with four different alleles for fur color in an animal, Da, Db, Dc, and Dd. If you crossed two heterozygotes, DaDb and DcDd, what genotype proportions would you expect in the offspring?

25% DaDc, 25% DaDd, 25% DbDc, 25% DbDd

ABO blood type in humans exhibits codominance and multiple alleles. What is the likelihood of a type A father and a type A mother having a type O child?

25% if both parents are heterozygous

Flower color in snapdragons is an example of incomplete dominance. When a red-flowered plant is crossed with a white-flowered plant, the F1 generation has pink flowers. If a pink-flowered plant is crossed with another pink-flowered plant, the progeny plants will be __________.

25% red, 50% pink, and 25% white

The agouti gene in mice plays a role in determining coat color. At this locus, the genotype AA produces an "agouti coat," and the heterozygote Aa produces a yellow coat. The aa homozygotes, however, die very early in development. What is the expected phenotypic ratio of live mice resulting from a cross of two Aa mice?

2:1 yellow:agouti

Consider the case of recessive epistasis in Labrador coat color. Suppose you were to cross a black lab (genotype BbEe) with a brown lab (genotype bbEe). What is the expected distribution of coat color among the offspring?

3:3:2 black:brown:yellow

An individual with the genotype AABbCcDD can make how many different kinds of gametes?

4

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?

50%

John, age 47, has just been diagnosed with Huntington's disease, which is caused by a rare dominant allele. His daughter, age 25, has a 2-year-old son. No one else in the family has the disease. What is the probability that the daughter will develop the disease?

50%

Imagine a cross of two triple heterozygous pea plants with tall stems and axial purple flowers (genotype TtAaPp). If you were to create a Punnett square for this cross (this is not a recommended strategy!), what would be its dimensions? Recall that all three loci assort independently.

8 × 8

Human blood groups are governed by three alleles: IA, IB, and i. IA and IB are codominant and i is recessive to both. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes?

A, B, AB, or O

In a certain plant, the alleles A, B, and C are completely dominant to the alleles a, b, and c. A plant with the genotype AABbcc will have the same phenotype as a plant with the genotype __________.

AaBBcc

Which of the following properties were present in the characters that Mendel examined in his breeding experiments?

All of the listed responses are correct

A man has a pointed frontal hairline known as a widow's peak. This trait is thought to be controlled by a dominant allele. His wife lacks a widow's peak, and their son has a widow's peak. (W: widow's peak; w: no widow's peak). The son is curious about whether his father is homozygous or heterozygous for the widow's peak trait. Which of the following facts would allow him to know?

His father's mother lacks a widow's peak

How does codominance at the molecular level help to explain why evolutionary processes haven't resulted in the elimination of the sickle-cell allele among people of African descent?

Individuals with normal and sickle-cell hemoglobin in their red blood cells are usually healthy and, when infected by the malaria parasite have lower parasite densities and, thus, reduced malaria symptoms.

Which of the following matings CANNOT produce a child with blood type O? The letters refer to blood types (phenotypes).

O x AB

The Rh blood factor in humans is perhaps the most important after the ABO system. The + phenotype is dominant to the - phenotype and is encoded on a separate autosome from the ABO locus (i.e., the two loci assort independently). A child is born to a woman of blood type A+ and a man of blood type AB+. Which of the following blood types would not be possible for the child?

O+

Which of the following is not a reason that peas were well suited for Mendel's breeding experiments?

Peas have an unusually long generation time.

A couple, both descended from eastern European (Ashkenazic) Jews, visit a genetic counselor before trying to have children. In view of their ethnic background, the counselor recommends that they be tested to see if they are carriers for __________.

Tay-Sachs disease

The law of independent assortment __________.

The first, second, and third answers are correct

Cystic fibrosis, which is usually lethal before the age of reproduction, is a homozygous recessive trait. Why do cases continue to arise, even though people with the disease rarely live to reproduce?

The harmful allele "hides" within heterozygous individuas, and one-fourth of the offspring of two heterozygotes would be afflicted

What kind of protection does the Genetic Information Nondiscrimination Act of 2008 provide the public with regard to the use of genetic information?

The law prohibits the use of genetic test information to deny insurance coverage or employment to individuals

What is indicated when a single-character testcross yields offspring that all have the dominant phenotype?

The parent with the dominant phenotype was homozygous

Pea plants are tall if they have the genotype TT or Tt, and they are short if they have genotype tt. A tall plant is mated with a short plant. Which outcome below would indicate that the tall parent plant was heterozygous?

The ratio of tall offspring to short offspring is 1:1

Huntington's disease is an example of a genetic disorder caused by __________.

a lethal dominant allele that afflicts an individual later in life

When two average-height parents give birth to a child exhibiting achondroplasia, it is most likely due to a new mutation. This is because

achondroplasia is caused by an allele that is always expressed; therefore the parents must not have the allele

Assume tall (T) is completely dominant to dwarf (t) in a certain species of plant. If a homozygous dominant individual is crossed with a homozygous dwarf, the offspring will____.

all be tall

The F1 generation differed from the F2 in Mendel's experiments in that

all of the F1 showed the dominant phenotype, but only three-quarters of the F2 did

If an organism that is homozygous dominant is crossed with a heterozygote for that trait, the offspring will be __________.

all of the dominant phenotype

Fetal cells may be removed along with fluid from the womb by a process known as __________.

amniocentesis

Examine this genetic pedigree. What mode of inheritance does this trait most likely follow?

autosomal recessive

Mendel's theory of particulate inheritance __________.

can explain inheritance patterns for virtually every sexually reproducing organism but does not explain multifactorial characters

A red bull is crossed with a white cow and all of the offspring are roan, an intermediate color that is caused by the presence of both red and white hairs. This is an example of genes that are __________.

codominant

Homologous pairs of chromosomes often __________..

contain different alleles

Physically, what are different alleles?

different alleles are different DNA sequences found at the same locus on homologous chromosomes

A cross between homozygous purple-flowered and homozygous white-flowered pea plants results in offspring with purple flowers. This demonstrates

dominance.

The genetic disease cystic fibrosis is caused by a defective allele that

encodes a defective chloride-channel membrane transport protein

Tay-Sachs disease runs in Rebecca's family. On a family pedigree, she saw a shaded circle. This represented a __________.

female with Tay-Sachs

A pea plant is heterozygous at the independent loci for flower color (Pp) and seed color (Yy). What types of gametes can it produce?

four gamete types: pY, py, PY, and Py

Look around the campus. Which of the following human phenotypes can likely be considered to be polygenic?

height hair color eye color skin color all of the above

If a plant variety is true-breeding for a dominant trait, then

if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait

Which choice below describes the expression of Tay-Sachs disease in humans at the biochemical level?

incompletely dominant

Heart disease, diabetes, cancer, alcoholism, and many mental illnesses can best be described as __________.

multifactorial disorders with a possible polygenic component

A phenotypic trait that is dependent on several genes and environmental conditions is said to be

multifactorial.

A single genetic locus that controls more than one trait is said to be

pleiotropic

Tail length in a certain species of armadillo falls along a continuum; a plot of tail length versus frequency displays a normal distribution. Assuming that environmental factors do NOT play an important role in determining tail length, this type of variation probably reflects __________.

polygenic inheritance

In Mendel's monohybrid cross of purple-flowered and white-flowered peas, all members of the F1 generation had the __________ phenotype because their genotype was __________ at the flower-color locus.

purple-flowered...heterozygous

It is far more common to find human genetic disease caused by __________ alleles than by __________ alleles because __________.

recessive... domiant... harmful recessive alleles can survive in the heterozygote without any selection pressure against them

In people with sickle-cell disease, red blood cells break down, clump, and clog the blood vessels. The blood vessels and the broken cells accumulate in the spleen. These events lead to physical weakness, heart failure, joint pain, and brain damage. Such a suite of symptoms can be explained by

the pleiotropic effects of the sickle-cell allele

If the two traits that Mendel looked at in his dihybrid cross of smooth yellow peas with wrinkled green peas had been controlled by genes that were located near each other on the same chromosome, then the F2 generation

would have deviated from the 9:3:3:1 phenotypic ratio that is predicted by the law of independent assortment

Color in squash is controlled by epistatic interactions in which color is recessive to no color. At the first locus, white squash (W) is dominant to colored squash (w). At the second locus, yellow (Y) is dominant to green (y). What is the phenotype of a squash with the genotype wwYy?

yellow

Imagine the same cross of two triple heterozygous pea plants with tall stems and axial purple flowers (genotype TtAaPp). Using the rules of probability (and not a Punnett square), determine what proportion of offspring will have dwarf stems and axial purple flowers.

¼ × ¾ × ¾ = 9/64

The following offspring were observed from many crossings of the same pea plants. What genotypes were the parents? 465 purple axial flowers 152 purple terminal flowers 140 white axial flowers 53 white terminal flowers

​PpAa × PpAa

In peas, the allele for tall stems (T) is dominant to that for dwarf stems (t), and the allele for axial flowers (A) is dominant to that for terminal flowers (a). A plant of unknown genotype with tall stems and axial flowers is crossed with a plant with dwarf stems and terminal flowers. Among the offspring are 38 plants with tall stems and axial flowers, and 36 plants with tall stems and terminal flowers. What is the previously unknown genotype?

​TTAa