Chapter 14 Practice test

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 x PpRr will have white flowers and wrinkled seeds? ( Concept 14.2) 0 1/16 1/4 3/4 1/2

1/16 Pp × Pp would produce 3/4 purple and 1/4 white. Rr × Rr would produce 3/4 round and 1/4 wrinkled; (1/4)(1/4) = 1/16 would have white flowers and wrinkled seeds.

If a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous? ( Concept 14.2) 1/4 1/3 1/2 2/3 all of them

1/2 One-quarter of the offspring will be homozygous for the dominant allele, one-quarter will be homozygous for the recessive allele, and the remaining half will be heterozygous.

Michelle and Keith are apparently normal, 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 _____. ( Concept 14.4) 0 1/4 1/2 2/3 3/4

1/4 Correct. The probability of their next child having alkaptonuria is one-fourth because they are both heterozygous (carriers) for the trait.

An AABbccDdEeFF individual is crossed with an individual with the genotype AaBBCCDdEeff. What is the probability that their offspring will have the genotype AaBBCcddEEFf? ( Concept 14.2) 1/2 1/4 1/16 1/32 1/64

1/64 Correct. To obtain the overall probability, multiply the individual probabilities for each locus: (1/2)(1/2)(1)(1/4)(1/4)(1) = 1/64.

If each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce? ( Concept 14.2) 10,000 200 1,000 100 1,000,000

10,000 100 × 100 = 10,000. The rule of multiplication applies to these independent events.

Tom's brother suffers from phenylketonuria (PKU), a recessive disorder. The brothers' parents do not have PKU. What are the chances that Tom, who is normal for this trait, is a carrier of PKU? ( Concept 14.4) 1/4 1/3 1/2 2/3 4/3

2/3 Correct. The parents must both be carriers of PKU. Tom, who is not affected, has a 1/3 chance of not being a carrier and a 2/3 chance of being a carrier.

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 _____. ( Concept 14.3) 100% pink 100% red 25% red, 50% pink, and 25% white 50% pink and 50% red 25% white and 75% red

25% red, 50% pink, and 25% white Breeding the F1 hybrids of the snapdragon cross produces F2 offspring, with a phenotypic ratio of 1 red: 2 pink: 1 white.

An individual with the genotype AABbCcDD can make how many different kinds of gametes? (Concept 14.2) 2 4 8 16 32

4 The individual varies only at loci B and C (not at A and D, which are homozygous), and there are two possible alleles at each loci (22 = 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? (Concept 14.3) 100% 75% 50% 25% 0%

50% The woman must be ii. 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, so he must have given him a recessive i allele.) The cross ii x IAi yields a 50% probability that the child will be ii, or type O.

Human blood groups are governed by three alleles, A, B, and O. A and B are codominant and O 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? ( Concept 14.3) A or B only AB only AB or O A, B, or O A, B, AB, or O

A, B, AB, or O The genotype of the man with type B blood could be IBIB or IBi, so his gametes could be IB or i. The genotype of the woman with type A blood could be IAIA or IAi, so her gametes could be IA or i.

A = big apples; R = red apples; a = small apples; r = yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half of the new trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents? ( Concept 14.1) AArr and aaRr Aarr and aaRr AARr and Aarr AaRr and AaRr AaRr and aarr

AArr and aaRr Trees that produce big yellow apples could be AArr or Aarr. Trees that produce small red apples could be aaRR or aaRr. Because all the offspring are big, the big parent must be homozygous for A. Because half the apples are red and half are yellow, the red parent must be heterozygous for red. The conclusion is that the cross must be AArr x aaRr.

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 _____. ( Concept 14.1) Aabbcc aabbcc AaBBcc AABBCc None of the listed responses is correct.

AaBBcc Correct. Individuals with one or two dominant alleles at a locus are indistinguishable, so AA and Aa have the same phenotype (as do BB and Bb).

In carrying out his breeding studies, Mendel examined characters that had which of the following properties? ( Concept 14.1) They were controlled by loci that were (or behaved as if they were) on different chromosomes. It was possible to isolate true-breeding varieties for each trait. The traits varied in an either-or fashion. The characters each were controlled by a single gene. All of the listed responses are correct.

All of the listed responses are correct.

Physically, what are different alleles? ( Concept 14.1) Different alleles are different DNA sequences found at the same locus on sister chromatids. Different alleles are different particles found in gametes. Different alleles are different phenotypes for a particular character. Different alleles are different DNA sequences found at the same locus on homologous chromosomes. None of the listed responses is correct.

Different alleles are different DNA sequences found at the same locus on homologous chromosomes. Correct. From a physical standpoint, an allele is a variant of a DNA sequence that codes for a particular gene.

A man who can roll his tongue and a woman who cannot roll her tongue have a son who can roll his tongue (R = can roll tongue; r = can't roll tongue). The son is curious about whether his father is homozygous or heterozygous for the tongue-rolling trait. Which of the following facts would allow him to know? ( Concept 14.4) His father's mother cannot roll her tongue. His paternal grandfather and his paternal grandmother can both roll their tongues. The son's sister is a tongue roller. The son's own daughter cannot roll her tongue. The son submits his own blood sample to a local genotyping lab, and they establish that he is heterozygous for the trait.

His father's mother cannot roll her tongue. Correct. If his father's mother cannot roll her tongue, then his father must be heterozygous.

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? ( Concept 14.4) Individuals with two sickle-cell alleles are immune to infection by the malaria parasite. The presence of both normal and sickle-shaped hemoglobin in the red blood cells of heterozygous individuals provides immunity to infection by the malaria parasite. Individuals only need one normal allele to have completely normal hemoglobin and reduced densities of malaria parasites in their red blood cells. 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. None of the listed responses is correct.

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. The presence of both normal and sickle-cell hemoglobin reflects a codominance of normal and sickle-cell traits in heterozygous individuals. By carrying only one sickle-cell allele, an individual is usually healthy and is protected from the lethal effects of malarial. Thus, the allele is retained in the population by this selective advantage. The prevalence of the allele among African-Americans is a remnant of their ancestry in Africa, where malaria is common.

Which of the following matings cannot produce a child with blood type O? The letters refer to blood types (phenotypes). ( Concept 14.3) A × A A × B O × AB O × O None of the listed responses is correct.

O × AB Every child of an AB individual will carry either the A or the B allele.

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 _____. ( Concept 14.4) cystic fibrosis hemophilia sickle-cell disease hypercholesterolemia Tay-Sachs

Tay-Sachs There is a disproportionately high incidence of Tay-Sachs disease among Ashkenazic Jews.

Which choice below is a basic difference between Mendel's particulate hypothesis and the hypothesis of blending inheritance? ( Concept 14.1) The blending inheritance hypothesis, but not the particulate hypothesis, maintained that mutation is the major source of new gene combinations. The blending inheritance hypothesis, but not the particulate hypothesis, maintained that the two alleles at any given locus are always different. The blending inheritance hypothesis, but not the particulate hypothesis, maintained that the traits governed by genes in the egg are different from the traits governed by genes in the sperm. The blending inheritance hypothesis, but not the particulate hypothesis, maintained that after a mating, the genetic material provided by each of the two parents is mixed in the offspring, losing its individual identity. All of the listed responses are correct.

The blending inheritance hypothesis, but not the particulate hypothesis, maintained that after a mating, the genetic material provided by each of the two parents is mixed in the offspring, losing its individual identity. Correct. The blending hypothesis maintained that the genetic material contributed by the two parents mixes in a manner analogous to the way blue and yellow paints blend to make green.

The law of independent assortment _____. ( Concept 14.1) states that the alleles at different loci segregate independently from one another during a dihybrid cross can account for a 9:3:3:1 ratio seen in the F2 generation applies only to genes that are present on different chromosomes (or behave as if they were) The first and second answers are correct. The first, second, and third answers are correct.

The first, second, and third answers are correct. states that the alleles at different loci segregate independently from one another during a dihybrid cross can account for a 9:3:3:1 ratio seen in the F2 generation applies only to genes that are present on different chromosomes (or behave as if they were) All of these are criteria of the law of independent assortment.

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? (Concept 14.4) New mutations continually introduce this harmful condition into the population. The harmful allele "hides" within heterozygous individuals, and one-fourth of the offspring of two heterozygotes would be afflicted. Mosquitoes can transfer the disease from person to person. People continue to make inappropriate lifestyle choices. None of the listed responses is correct.

The harmful allele "hides" within heterozygous individuals, and one-fourth of the offspring of two heterozygotes would be afflicted. Cystic fibrosis is inherited as a Mendelian recessive trait. Affected individuals usually have unaffected parents, both of whom are carriers of the recessive allele.

What kind of protection does the Genetic Information Nondiscrimination Act of 2008 provide the public with regard to the use of genetic information? ( Concept 14.4) The law guarantees that access to genetic counseling cannot be denied to U.S. citizens based on their race, sex, age, religious beliefs, or sexual orientation. The law prohibits the use of genetic test information to deny insurance coverage or employment to individuals. The law mandates that people who undergo genetic testing are provided professional instruction so that they can make informed family decisions based on their test results. The law mandates that all expecting mothers must undergo fetal testing for genetic disorders regardless of their demographic status.

The law prohibits the use of genetic test information to deny insurance coverage or employment to individuals. Correct. The law was enacted to allay fears by people opting for genetic testing that the results from such tests could be used against them by health insurance companies or potential employers.

What is indicated when a single-character testcross yields offspring that all have the dominant phenotype? ( Concept 14.1) The parent with the dominant phenotype was homozygous. The parent with the dominant phenotype was heterozygous. Epistasis has occurred. The alleles are codominant. Both parents are heterozygous.

The parent with the dominant phenotype was homozygous. If all the progeny show the dominant phenotype, the parent must have been homozygous, transmitting the dominant allele to all of the offspring.

Huntington's disease is an example of a genetic disorder caused by _____. ( Concept 14.4) a lethal dominant allele that afflicts an individual later in life a nonlethal dominant allele a late-acting recessive allele homozygous recessive alleles multiple alleles

a lethal dominant allele that afflicts an individual later in life Correct. By the time symptoms are evident, the individual may have already transmitted the allele to his or her children.

When two average-height parents give birth to a child exhibiting achondroplasia, it is most likely due to a new mutation. This is because _____. ( Concept 14.4) the frequency of achondroplasia is unknown achondroplasia is a relatively rare disorder achondroplasia is caused by an allele that is always expressed, therefore the parents must not have the allele such mutations are statistically predictable None of the listed responses is correct.

achondroplasia is caused by an allele that is always expressed, therefore the parents must not have the allele Achondroplasia, a form of dwarfism, is due to a dominant 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 _____. ( Concept 14.1) all be intermediate in height all be tall be 1/2 tall and 1/2 dwarf be 3/4 tall and 1/4 dwarf all be short

all be tall Like Mendel's original purple with white cross, all the F1 offspring will show the dominant phenotype.

The F1 generation differed from the F2 in Mendel's experiments in that _____. ( Concept 14.1) all of the F1 showed the dominant phenotype, whereas only half of the F2 did all of the F1 showed the dominant phenotype, but only three-fourths of the F2 did all of the F1 showed the dominant phenotype, and all of the F2 showed the recessive phenotype one-half of the F1 showed the dominant phenotype, and three-fourths of the F2 did none of the F1 showed the dominant phenotype, but one-half of the F2 did

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

If an organism that is homozygous dominant is crossed with a heterozygote for that trait, the offspring will be _____. ( Concept 14.1) all of the dominant phenotype 1/4 of the recessive phenotype all homozygous dominant all homozygous recessive present in a 9:3:3:1 ratio

all of the dominant phenotype The offspring of an AA x Aa cross are either AA or Aa. All will express the dominant phenotype.

Fetal cells may be removed along with fluid from the womb by a process known as _____. ( Concept 14.4) karyotyping testcrossing amniocentesis sonogramming chorionic villus sampling

amniocentesis Correct. In amniocentesis, a small amount of the amniotic fluid is extracted for testing.

Mendel's theory of particulate inheritance _____. ( Concept 14.3) can explain inheritance patterns for virtually every sexually reproducing organism but does not explain multifactorial characters cannot explain epistasis only applies to alleles that are strictly dominant or recessive can explain incomplete dominance but fails to explain multiple alleles explains how genotype is expressed as phenotype

can explain inheritance patterns for virtually every sexually reproducing organism but does not explain multifactorial characters Correct. Although many patterns of inheritance have been discovered, they can still be explained using the concept of alleles (Mendel's hereditary "particles"). Multifactorial characters are influenced by environmental influences, so they are not strictly governed by Mendel's theory.

In which genetic testing procedure would a physician remove a small tissue sample from a membrane of fetal genetic origin? ( Concept 14.4) chorionic villus sampling amniocentesis fetoscopy ultrasound None of the listed responses is correct.

chorionic villus sampling The cells sampled are derived from the fetus; therefore, a karyotype of the fetus can be created using these cells.

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 _____. (Concept 14.3) nonhomologous epistatic codominant polygenic completely dominant

codominant Correct. Roan is caused by the presence of both red and white hairs.

Homologous pairs of chromosomes often _____. ( Concept 14.1) carry different genes for different traits differ in length contain different alleles are not both present in diploid somatic cells are paired up in the G2 phase of the cell cycle

contain different alleles Homologous chromosomes may carry different alleles at one or more loci.

The genetic disease cystic fibrosis is caused by a defective allele that _____. ( Concept 14.4) encodes a dysfunctional enzyme that fails to break down brain lipids causes hemoglobin molecules to malfunction encodes a defective chloride-channel membrane transport protein encodes a neurotoxin encodes an enzyme that breaks down muscle fibers

encodes a defective chloride-channel membrane transport protein Correct. The absence of the transport protein leads to a high concentration of extracellular chloride, causing a thick, sticky mucus to accumulate outside of cells. This mucus interferes with the normal function of numerous organs.

Tay-Sachs disease runs in Rebecca's family. On a family pedigree, she saw a shaded circle. This represented a _____. ( Concept 14.4) male with Tay-Sachs female carrier male carrier female with Tay-Sachs male of unknown genotype

female with Tay-Sachs Correct. The circle indicates a female and the shading indicates the disease.

If a plant variety is true-breeding for a dominant trait, then _____. ( Concept 14.1) if the plant were allowed to self-pollinate, the dominant and recessive traits would consistently appear in a 3:1 ratio among the progeny the plant is heterozygous for the trait if the plant were crossed with a heterozygote, one-half of the progeny would show the dominant trait, and one-half would show the recessive trait if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait the variety is unable to mutate

if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait True-breeding means that self-pollination would produce progeny that all have the same phenotype as the parent. In this case, the parent shows the dominant trait, so the progeny would as well.

Which choice below describes the expression of Tay-Sachs disorder in humans at the biochemical level? ( Concept 14.3) dominant incompletely dominant codominant recessive polygenic

incompletely dominant This is the phenotype observed at the biochemical level. The activity level of the lipid-metabolizing enzyme in heterozygotes is intermediate.

Heart disease, diabetes, cancer, alcoholism, and many mental illnesses can best be described as _____. ( Concept 14.4) simple Mendelian disorders infectious diseases caused by microorganisms multifactorial disorders with a possible polygenic component the symptoms of Huntington's disease the results of an unhealthy lifestyle

multifactorial disorders with a possible polygenic component Correct. These disorders involve several genes and environmental factors.

A single genetic locus that controls more than one trait is said to be _____. ( Concept 14.3) polygenic epistatic pleiotropic a quantitative character somatic

pleiotropic Correct. The ability of a gene to affect an organism in multiple ways is called pleiotropy.

Tail length in a certain species of armadillo falls along a continuum, following a normal distribution. Assuming that environmental factors do not play an important role in determining tail length, this type of variation probably reflects _____. ( Concept 14.3) polygenic inheritance pleiotropy epistasis complete dominance incomplete dominance

polygenic inheritance Characters that vary along a continuum, following a normal distribution, are often controlled by multiple genes, each contributing to the phenotype in an additive fashion.

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. (Concept 14.1) white-flowered ... homozygous recessive white-flowered ... heterozygous purple-flowered ... homozygous recessive purple-flowered ... homozygous dominant purple-flowered ... heterozygous

purple-flowered ... heterozygous All F1 individuals of the purple x white cross were phenotypically purple and heterozygous (Pp).

It is far more common to find human genetic disease caused by _____ alleles than by _____ alleles because _____. ( Concept 14.4) dominant ... recessive ... dominant alleles have an evolutionary advantage over recessive alleles dominant ... recessive ... dominant alleles became dominant because they aid the survival of the organism carrying them recessive ... dominant ... harmful recessive alleles can survive in the heterozygote without any selection pressure against them recessive ... dominant ... even when homozygous, recessive alleles usually do not cause as much damage as dominant alleles None of the listed responses is correct.

recessive ... dominant ... harmful recessive alleles can survive in the heterozygote without any selection pressure against them Lethal dominant alleles are much less common than lethal recessive ones because the effects of lethal dominants are not masked in heterozygotes.

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. Among other things this leads to physical weakness, heart failure, joint pain, and brain damage. Such a suite of symptoms can be explained by _____. ( Concept 14.4) the polygenic nature of sickle-cell disease the pleiotropic effects of the sickle-cell allele an epistatic interaction between the sickle-cell allele and a proteolytic enzyme gene a bacterial infection interacting with the sickle-cell allele side effects of the drugs used to cure sickle-cell disease

the pleiotropic effects of the sickle-cell allele Correct. Pleiotropy refers to the ability of certain genes to affect multiple characters.

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? ( Concept 14.1) All of the offspring are short. All of the offspring are tall. The ratio of tall offspring to short offspring is 3:1. The ratio of tall offspring to short offspring is 1:1. There is not enough information to answer the question.

the ratio of tall offspring to short offspring is 1:1. Half of the offspring would be heterozygous and the other half homozygous recessive.

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 _____. ( Concept 14.1) would have contained four phenotypes in a 9:3:3:1 ratio would have contained only individuals that were heterozygous at both loci would have deviated from the 9:3:3:1 phenotypic ratio that is predicted by the law of independent assortment would have contained no individuals that were heterozygous at both loci None of the listed responses is correct.

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? ( Concept 14.3) white green with yellow stripes green yellow white with yellow stripes

yellow The genotype at the first locus is homozygous recessive for colored squash, and the genotype at the second locus is heterozygous. Yellow is dominant. Therefore, the squash is yellow.