Chapter 15 Practice Test

The chromosome theory of inheritance states that _____. ( Concept 15.1)

genes occupy specific positions on chromosomes
homologous chromosomes segregate from each other during meiosis
chromosomes assort independently during meiosis
The first and second answers are correct.
The first, second, and third answers are correct.

The first, second, and third answers are correct. The theory encompasses these three basic elements.

Why did Morgan choose Drosophila for his genetics experiments? ( Concept 15.1)

They have a long generation time.
A single mating can produce many offspring.
They have a large number of chromosomes.
Drosophila chromosomes can be easily distinguishable under a light microscope.
Both the second and fourth answers are correct.

Both the second and fourth answers are correct. The small number of chromosomes and the large number of offspring per mating contribute to Drosophila’s usefulness as an experimental animal for genetics experiments.

Wild type refers to _____. ( Concept 15.1)

a kind of chromosomal deletion
the most extreme mutant phenotype observed in an experiment
extranuclear genes
any mutant genotype
the most common phenotype thought to be found in the natural population

: the most common phenotype thought to be found in the natural population The wild type is the phenotype most often seen in the wild.

Which of the following results of Thomas Hunt Morgan’s experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics? ( Concept 15.1)

The mutant allele (white eyes) was recessive.
Among the F2 progeny, only males had white eyes. All of the females had red eyes.
The F1 flies were crossed with each other, and the F2 progeny included red-eyed and white-eyed flies in a 3:1 ratio.
In the parental cross, a white-eyed male was crossed with a red-eyed female. The F1 progeny all had red eyes.
all of the above

Among the F2 progeny, only males had white eyes. All of the females had red eyes. This result was unexpected and led to the discovery of sex-linked genes.

What is the probability that a male will inherit an X-linked recessive allele from his father? ( Concept 15.2)

0%
25%
75%
50%
100%

0% A male receives a Y chromosome from his father, not an X.

In an X-linked, or sex-linked, trait, it is the contribution of _____ that determines whether a son will display the trait. ( Concept 15.2)

the paternal grandfather
the mother
the father
the paternal grandmother
none of the above

the mother The son receives his single X chromosome from his mother and the Y from his father.

If a mother is heterozygous for a recessive sex-linked trait and her husband has the dominant allele, which one of the following is true about the probabilities for their children? ( Concept 15.2)

All of their daughters will be heterozygous.
Half of their sons will have the recessive trait.
All of their sons will have the recessive trait.
None of their sons will have the recessive trait.
none of the above

Half of their sons will have the recessive trait. All the sons will receive Y chromosomes from their father. The X must come from the heterozygous mother; therefore, each son has a 50% chance of inheriting the recessive allele.

In werewolves (hypothetically), pointy ears (P) are dominant over round ears (p). The gene is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears? ( Concept 15.2)

75%
50%
100%
25%
0%

50% The female werewolf must be heterozygous, because her father has round ears. Each of her sons has a 50% chance of inheriting the round allele.

A woman is red-green color-blind. What can we conclude, if anything, about her father? ( Concept 15.2)

He is red-green color-blind.
There is a 50% probability that he has normal vision.
We have too little information to tell.
He has two Y chromosomes.
none of the above

He is red-green color-blind. For the woman to be affected with this sex-linked recessive trait, she must be homozygous; therefore, she must have received a recessive allele from her father. The father’s single X must have the recessive allele.

A woman is a carrier for red-green color blindness, a sex-linked trait. Her husband is normal (not color-blind) for this trait. What are the chances that their newborn daughter will be red-green color-blind? (Concept 15.2)

75%
25%
50%
100%
0%

0% The daughter must receive one of her X chromosomes from her normal father and will not be color-blind.

Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls? (Concept 15.2)

The allele is carried on the Y chromosome.
To express an X-linked recessive allele, a female must have two copies of the allele.
Sex-linked traits are never seen in girls.
Nondisjunction occurs in males but not in females.
A sex-linked allele cannot be passed from mother to daughter.

To express an X-linked recessive allele, a female must have two copies of the allele. Moreover, males carrying the allele have less of an opportunity to have offspring.

Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a _____ probability of having hemophilia. ( Concept 15.2)

0%
33%
25%
50%
100%

50% The mother is XHXh, and the father is XhY. The daughter must receive Xh from the father and has a 50% chance of receiving Xh from the mother.

Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype? ( Concept 15.2)

Either her mother was a carrier or her father had hemophilia.
Either her mother was homozygous dominant or her father had hemophilia.
Either her mother was a carrier or her father had a dominant allele.
Both her mother and her father had hemophilia.
none of the above

Either her mother was a carrier or her father had hemophilia. Queen Victoria must have had the hemophilia allele on one of her X chromosomes. Either her mother was a carrier or her father was affected.

In a certain fish, fin rays (supporting structures for the fins) can be either bony or soft in adult fish. Sex linkage in a fish is similar to that in humans. What evidence would most strongly support the idea that the ray locus is on the X chromosome? ( Concept 15.2)

Females with bony rays cannot pass bony rays to female offspring even if they are mating with a bony ray male.
Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females.
Bony ray males can pass on bony rays only to their male offspring.
Females with either bony or soft rays can reproduce, but males with soft rays cannot transfer sperm to the female.
all of the above

Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females. Genes affecting sex-linked traits will give particular sex ratios in the offspring, and reciprocal crosses (males with the dominant trait crossed with females with the recessive trait, and males with the recessive trait crossed with females with the dominant trait) would not have the same results.

A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by _____. ( Concept 15.2)

RNA splicing
a homeobox
X chromosome inactivation
an operon
a mutation

X chromosome inactivation Inactive X chromosomes in the cells of a female condense into compact objects known as Barr bodies. All X chromosomes in excess of one are inactivated.

With a microscope, you examine some somatic cells from a woman and notice that each nucleus has two Barr bodies. What can you infer about the sex chromosomes in this individual? ( Concept 15.2)

She is XXXX.
She is XX.
She is XXX.
She is XXY, but the Y chromosome lacks the SRY gene.
none of the above

She is XXX.

X-linked genes differ from Y-linked genes in which of the following ways? ( Concept 15.2)

Though most X-linked genes determine sex, Y-linked genes control for characters unrelated to sex.
Only X-linked genes are technically sex-linked because Y-linked genes affect characteristics unrelated to sex.
Although the X and Y chromosomes carry genes that determine sexual characteristics, there are not corresponding regions of homology for genes located on each chromosome.
Sons and daughters have equal probabilities in inheriting a recessive allele of an X-linked gene from their mother, but only sons can inherit rare Y-linked genetic disorders from their father.
Sons and daughters can inherit alleles of X-linked genes from fathers proportionally but only sons inherit alleles of Y-linked genes from their fathers.

Sons and daughters have equal probabilities in inheriting a recessive allele of an X-linked gene from their mother, but only sons can inherit rare Y-linked genetic disorders from their father. Mothers can pass X-linked recessive alleles to both sons and daughters with equal probability. Because sons only inherit the one X chromosome from their mothers, they will express the recessive trait; the phenotype of daughters will depend on which X-linked allele they inherit from their fathers. Only sons inherit the Y chromosomes from their fathers, so Y-linked genetic disorders, although rare, will only affect sons.

Which of the following best describes the function of the XIST gene in X chromosome inactivation? (Concept 15.2)

The XIST gene codes for an enzyme that methylates DNA on the X chromosome being inactivated.
The XIST gene on the X chromosome to be inactivated is expressed to produce multiple RNA transcripts that bind to that chromosome and effectively cover it up, thereby generating a Barr body.
The XIST gene on the X chromosome to remain active is expressed to produce multiple RNA molecules that bind to the X chromosome to be inactivated and effectively cover it up, thereby generating a Barr body.
Together with other proteins, the product of the XIST gene binds to histones and induces supercoiling of the DNA in one of the X chromosomes, thus inactivating it.
The first and second listed responses are correct.

The XIST gene on the X chromosome to be inactivated is expressed to produce multiple RNA transcripts that bind to that chromosome and effectively cover it up, thereby generating a Barr body. Working with RNA products of other genes on the X chromosome to be inactivated, multiple copies of the RNA product of the XIST gene attach to the X chromosome in such a way that it is inactivated and becomes a Barr body.

If two genes are linked, _____. ( Concept 15.3)

they assort independently
they code for the same protein
they are on the same chromosome
they are on sex chromosomes
they are on different chromosomes

:they are on the same chromosome Genes located on the same chromosome are inherited together and are said to be linked.

In a particular species of mammal, black hair (B) is dominant to green hair (b), and red eyes (R) are dominant to white eyes (r). When a BbRr individual is mated with a bbrr individual, offspring are produced in a ratio of 5 black hair and red eyes:5 green hair and white eyes:1 black hair and white eyes:1 green hair and red eyes. Which of these explanations accounts for this ratio? ( Concept 15.3)

Green-haired individuals have a higher prenatal mortality than black-haired individuals.
The genes for both of these traits are carried on the autosomes.
The genes for hair color and the genes for eye color are carried on different chromosomes.
The expected results did not take genetic recombination into account.
The genes for hair color and eye color are linked.

The genes for hair color and eye color are linked. This explains why the parental types occur more often than would be expected if the traits assorted at random.

A gray-bodied, vestigial-winged fly is crossed with a black-bodied, normal-winged fly. The F1 progeny is testcrossed. Among the resulting offspring, _____ is a parental type, and _____ is a recombinant type. ( Concept 15.3)

black-bodied, normal-winged … black-bodied, normal-winged
gray-bodied, vestigial-winged … black-bodied, normal-winged
gray-bodied, normal-winged … black-bodied, vestigial-winged
black-bodied, normal-winged … black-bodied, vestigial-winged
gray-bodied, normal-winged … black-bodied, normal-winged

black-bodied, normal-winged … black-bodied, vestigial-winged The two parental types are gray-bodied, vestigial-winged and black-bodied, normal-winged, and the two recombinant types are gray-bodied, normal-winged and black-bodied, vestigial-winged.

You perform a testcross using F1 dihybrid flies. If, in the resulting offspring, the percentages of parental and recombinant offspring are about the same, this would indicate that the two genes are _____. (Concept 15.3)

mutated
linked
unlinked
similar in DNA sequence
imprinted

unlinked Two genes on different chromosomes assort independently.

The recombination frequency between two gene loci is _____. ( Concept 15.3)

dependent on whether dominant or recessive alleles are carried at the two loci
greater as the distance between the two loci decreases
equal to the size of the chromosome
greater as the distance between the two loci increases
dependent on the sex of the parent

greater as the distance between the two loci increases Correct. The farther apart two genes are, the higher the probability that a crossover will occur between them, and therefore the higher the recombination frequency.

Four genes (A, B, C, and D) are on the same chromosome. The recombination frequencies are as follows: A-B: 19%; B-C: 14%; A-C: 5%; B-D: 2%; A-D: 21%; C-D: 16%. Based on this information, which sequence of genes is correct? ( Concept 15.3)

ACBD
ABDC
ACDB
ADBC
ABCD

ACBD C must lie between A and B (5 +14 = 19). Similarly, D must be beyond B to be 21 units from A and 2 units from B.

In question 18, the observed distribution of offspring was as follows: black-red 1,070; black-white 177; green-red 180; green-white 1,072. Based on these data, what is the recombination frequency? ( Concept 15.3)

86%
approximately 14%
7%
30%
approximately 17%

:approximately 14% 177 + 180 = 357 recombinants. 357 recombinants/2,499 total offspring × 100 = 14% (approximately).

A linkage map _____. ( Concept 15.3)

predicts the probability that you will have a male or female child
orders genes on a chromosome based on recombination frequencies
can be constructed only for sex chromosomes
orders genes on a chromosome based on their location with respect to a stained band
shows the ordering and exact spacing of genes on a chromosome

orders genes on a chromosome based on recombination frequencies A linkage map presents the correct order of genes on the chromosome, although it is not necessarily an accurate representation of the actual distances between genes.

Because the frequency of crossing over is not uniform along the length of a chromosome, _____. (Concept 15.3)

pairs of homologous chromosomes contain small but significant differences in gene order
map units do not necessarily correlate to physical distances along the chromosome
the recombination frequency between two genes cannot be used to calculate the number of map units separating them
recombination frequency cannot be used to determine the number of centimorgans separating two genes
the centimorgan is an unreliable unit of measurement, and is rarely used today

map units do not necessarily correlate to physical distances along the chromosome Map units reflect recombination frequency, but not physical distance.

Which of the following would result in genetic variation by way of new combinations of alleles? (Concept 15.3)

independent alignment of homologous chromosomes during meiosis I
the exchange of alleles between homologous chromosomes during meiosis I
random fertilization increasing the number of possible allele combinations in an individual
The first and second responses are correct.
The first three responses are correct.

The first three responses are correct. Correct. Independent alignment of homologous chromosomes, crossing over, and random fertilization of gametes are all processes that occur in sexual fertilization and serve to increase genetic variation in a population by recombining alleles to generate new genotypes in individuals and new raw material for natural selection to act on.

As an expecting mother of 42 years of age, you are saddened to learn that the results of a prenatal test came back positive for trisomy 21. Although you are distraught by your circumstances, you are somewhat relieved to find out that the Prenatally and Postnatally Diagnosed Conditions Awareness Act was enacted to _____.( Concept 15.4)

address the alarming increase in Down syndrome in recent years among women between the ages of 40 and 45 who underwent prenatal testing in their first trimester
require medical practitioners to provide up-to-date, evidence-based information to parents about any prenatal or postnatal diagnosis for a trisomy condition, and connect the parents with appropriate support services
recognize individuals with Down syndrome as valuable contributors to their communities and provide legal protection to such individuals against discrimination by health care companies and employers
help offset the financial cost of treating and correcting this disorder
The second and third listed responses are correct.

require medical practitioners to provide up-to-date, evidence-based information to parents about any prenatal or postnatal diagnosis for a trisomy condition, and connect the parents with appropriate support services Principally, the law was enacted to assist those parents who have received a positive test diagnosis for Down syndrome or some other prenatally or postnatally diagnosed condition in two ways: 1) Require medical practitioners to inform parents of the possible science-based outcomes of such a condition (i.e. life expectancy, intellectual and functional development, and treatment options for a fetus diagnosed with, or a child born with, such conditions); and (2) Stipulate that medical practitioners connect parents with support service providers.

Individuals with an extra X chromosome _____. ( Concept 15.4)

may have subnormal intelligence or be at risk for learning disabilities
are always female
are generally sterile
have distinguishing physical features
None of the listed responses is correct.

may have subnormal intelligence or be at risk for learning disabilities Having an extra X chromosome affects males much more than females. In males, the extra X chromosome causes Klinefelter syndrome: abnormally small testes and sterility; some breast enlargement and other female body characteristics; and intelligence may be subnormal. Trisomy X females are normal for the most part, although they may be taller than average and may demonstrate learning disabilities.

During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____. ( Concept 15.4)

gametic infertility
sticky chiasmata
cellular sterility
nondisjunction
meiotic failure

nondisjunction In nondisjunction, chromosomes fail to separate properly at meiosis.

In Klinefelter syndrome, individuals are phenotypically male, but they have reduced sperm production and may have some breast development in adolescence. The cells of Klinefelter individuals have two X chromosomes and one Y (they are XXY instead of XY). This occurs because of what meiotic error? (Concept 15.4)

translocation
aneuploidy
monosomy
duplication
polyploidy

aneuploidy Correct. Aneuploidy is a chromosomal condition in which one or more chromosomes are present in extra copies or are deficient in number.

Cells that have a number of chromosomes different from the normal number for their species are known as _____. ( Concept 15.4)

trisomy
nanoploid
diploid
aneuploid
polyploid

aneuploid Any deviation in chromosome number is called aneuploidy.

_____ is usually less severe than _____, and _____ species have been observed in plants, fish, amphibians, and even mammals. ( Concept 15.4)

Monosomy … trisomy … monosomic
Nondisjunction … disjunction … nondisjunctional
Trisomy … monosomy … trisomic
Aneuploidy … polyploidy … aneuploid
Polyploidy … aneuploidy … polyploid

Polyploidy … aneuploidy … polyploid Correct. Polyploidy appears to disrupt genetic balance less than aneuploidy, and it has been observed among animals and especially plants.

Gene A is normally found on chromosome number 15 in humans. If amniocentesis reveals fetal cells containing gene A on chromosome 17, but not on 15, the best explanation would be that _____. (Concept 15.4)

at least one parent probably had a genetic syndrome
crossing over occurred during synapsis of meiosis I in one parent’s gametes
an inversion of gene A occurred on chromosome 15
base substitution occurred either during gametogenesis or in the mitotic divisions following fertilization
translocation occurred

translocation occurred Fragments produced by chromosomal breakage may join nonhomologous chromosomes, a rearrangement known as a translocation.

The chromosomal abnormality in which a fragment of a chromosome breaks off and then reattaches to the original chromosome in the same place but in the reverse direction is called _____. ( Concept 15.4)

translocation
transduction
transformation
inversion
duplication

inversion As the name suggests, an inversion is a backward piece of a chromosome.

Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16? ( Concept 15.4)

Extra copies of the other chromosomes are probably fatal to the developing embryo.
Down syndrome is not more common, just more serious.
There are probably more genes on chromosome 21 than on the others.
Chromosome 21 is a sex chromosome, and 3 and 16 are not.
Nondisjunction of chromosomes 3 and 16 probably occurs much less frequently.

: Extra copies of the other chromosomes are probably fatal to the developing embryo. Nearly all trisomies have lethal effects.

When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of _____ and results from _____. ( Concept 15.4)

genomic imprint … excessive methylation of either the paternal or maternal chromosome 21
aneuploidy … nondisjunction of chromosome 21 during meiosis I
polyploidy … occurrence of meiosis without cytokinesis
replication error … an extra cycle of DNA synthesis during the S phase
none of the above

aneuploidy … nondisjunction of chromosome 21 during meiosis I Correct. One aneuploid condition, Down syndrome, is the result of an extra chromosome 21.

A person with two X chromosomes and one Y chromosome would appear to be _____. ( Concept 15.4)

both male and female
male
female
neither male nor female
any of the listed responses, depending on the number of other chromosomes

male The presence of the Y chromosome determines maleness in humans. A male with an extra X chromosome has Klinefelter syndrome.

Which of the following is the only known viable human monosomy? ( Concept 15.4)

XXY
XO
YO
XYY
XY

XO Turner’s syndrome, or XO, is the only viable human monosomy.

Which type of chromosomal alteration is responsible for the cri du chat syndrome? ( Concept 15.4)

genetic imprinting
inversion
translocation
duplication
deletion

deletion A specific deletion from chromosome 5 leads to this disorder, which is characterized by mental retardation, small head and unusual facial features, and a cry that sounds like a distressed cat.

What appears to be the mechanism for genomic imprinting? ( Concept 15.5)

DNA methylation that silences particular genes
crossing over
DNA methylation that activates particular genes
nondisjunction
both the first and third listed responses

both the first and third listed responses Correct. DNA methylation appears to be the major mechanism involved in genomic imprinting, but in come cases it silences a gene and in others it activates a gene.

Genomic imprinting in mammals appears to affect primarily genes involved in _____. ( Concept 15.5)

function of the nervous system
vision
embryonic development
digestion
sex determination

embryonic development Igf2 is an example of a growth factor required for normal prenatal development. Experiments have also shown that organisms with improperly imprinted genes often die before birth.

Both chloroplasts and mitochondria _____. ( Concept 15.5)

display a Mendelian pattern of inheritance
are inherited from both parents
have linear DNA
are found within the nucleus
carry extranuclear genes

carry extranuclear genes Both chloroplasts and mitochondria carry extranuclear genes.

It is proposed that a certain disorder affecting the inner ear is caused by mitochondrial DNA. Which of the following observations would be the most decisive evidence against this idea? ( Concept 15.5)

Fathers with the disorder pass it on to all their children, but mothers with the disorder do not pass it along.
Females and males have the disorder in equal numbers.
The precise cause of the disorder is found to involve the nervous system.
Mothers pass the disorder on to their offspring, but fathers do not.
All of the above would be evidence against mitochondrial inheritance of this condition.

Fathers with the disorder pass it on to all their children, but mothers with the disorder do not pass it along. Maternal inheritance is the rule for mitochondrial genes in mammals, because the mitochondria in the zygote all come from the cytoplasm of the egg.

A person’s remains are found, and officials are trying to identify them. A couple believes that the remains belong to their missing daughter. Because the remains have decayed considerably, mitochondrial DNA is being used to determine the person’s identity. In order to determine if the remains belong to someone in this couple’s family, whose mitochondrial DNA should be used for comparison? ( Concept 15.5)

either the husband’s or the wife’s
Anyone from the same family will have nearly identical mitochondrial DNA.
one of the couple’s other children
the husband’s mother
the husband’s

one of the couple’s other children Because mitochondrial DNA all comes from the egg, a mother passes essentially the same mitochondrial DNA to each of her children. A child from the same family should be nearly identical.