AP Bio: Chapter 12 review

A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be a hemophiliac?

0

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? •0% •25% •50% •75% •100%

0%

What is the probability that a male will inherit an X-linked recessive allele from his father? •0% •25% •50% •75% •100%

0%

Humans are diploid and have 46 chromosomes (or two sets). How many sets of chromosomes are found in each human gamete? •1 •2 •3 •4 •5

1

A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. If the couple has four sons, what is the probability that all four will be born with hemophilia?

1/16

A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a son will be a hemophiliac?

1/2

Red-green color blindness is caused by a sex-linked recessive allele. A man with red-green color blindness marries a woman with normal vision whose father was color-blind. What is the probability that their first son will be color-blind?

1/2

Red-green color blindness is caused by a sex-linked recessive allele. A man with red-green color blindness marries a woman with normal vision whose father was color-blind. What is the probability that they will have a color-blind daughter?

1/4

A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive. They have a daughter who is a dwarf with normal color vision. What is the probability that she is heterozygous for both genes? • 50% • 0% • 100% • 75% • 25%

100%

Humans are diploid and have 46 chromosomes. How many chromosomes are found in each human gamete? •12 •23 •36 •45 •92

23

A particular diploid plant species has 48 chromosomes, or two sets. A mutation occurs and gametes with 48 chromosomes are produced. If self-fertilization occurs, the zygote will have _____ set(s) of chromosomes. •1 •2 •3 •4 •5

4

Assume that genes A and B are on the same chromosome and are 50 map units apart. An animal heterozygous at both loci is crossed with one that is homozygous recessive at both loci. What percentage of the offspring will show recombinant phenotypes resulting from crossovers?

50

Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a _____ probability of having hemophilia. •100% •25% •50% •0% •33%

50%

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? •0% •25% •50% •75% •100%

50%

f a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred? •A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell. •A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell. •A nondisjunction error occurred in meiosis I, in which both members of all homologous pairs migrated to the same pole of the cell. •No error occurred; these are normal gametes.

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.

If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred? •A nondisjunction error occurred in meiosis I, in which both members of all homologous pairs migrated to the same pole of the cell. •A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell. •No error occurred; these are normal gametes. •A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

What kind of cell results when a diploid and a haploid gamete fuse during fertilization? •A trisomic cell •A monosomic cell •A monoploid cell •A triploid cell

A triploid cell

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? •ABCD •ABDC •ACBD •ACDB •ADBC

ACBD

When can nondisjunction occur? Choose the best answer. •In mitosis, when sister chromatids fail to separate •In meiosis, when homologous chromosomes fail to separate •In meiosis, when sister chromatids fail to separate •All three answers are correct.

All three answers are correct.

Which of the following results of Thomas Hunt Morgan's experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics? •In the parental cross, a white-eyed male was crossed with a red-eyed female. The F1 progeny all 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. •The mutant allele (white eyes) was recessive. •Among the F2 progeny, only males had white eyes. All of the females had red eyes. •all of the above

Among the F2 progeny, only males had white eyes. All of the females had red eyes.

What is a nondisjunction? •None of the above •An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell •An error in which a diploid cell or organism has an extra chromosome of one type, producing a chromosome number of 2n + 1 •An error in which a diploid cell or organism lacks a chromosome of one type, producing a chromosome number of 2n - 1

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell

Why did Morgan choose Drosophila for his genetics experiments? •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.

Recombination between linked genes comes about for what reason? •Independent assortment sometimes fails because Mendel had not calculated appropriately. •Mutation on one homolog is different from that on the other homolog. •Crossovers between these genes result in chromosomal exchange. •When genes are linked they always "travel" together at anaphase. •Nonrecombinant chromosomes break and then re-join with one another.

Crossovers between these genes result in chromosomal exchange

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

Either her mother was a carrier or her father had hemophilia.

Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16? •There are probably more genes on chromosome 21 than on the others. •Chromosome 21 is a sex chromosome, and 3 and 16 are not. •Down syndrome is not more common, just more serious. •Extra copies of the other chromosomes are probably fatal to the developing embryo. •Nondisjunction of chromosomes 3 and 16 probably occurs much less frequently.

Extra copies of the other chromosomes are probably fatal to the developing embryo.

Imagine a human disorder that is inherited as a dominant, X-linked trait. How would the frequency of this disorder vary between males and females? •Males would display this disorder with greater frequency than females. •Females would display this disorder with greater frequency than males. •Males and females would display this disorder with equal frequency.

Females would display this disorder with greater frequency than males.

_____ is the process by which haploid gametes form a diploid zygote. •Embryogenesis •Meiosis •Gastrulation •Fertilization •Mitosis

Fertilization

Three genes (A, B, and C) at three loci are being mapped in a particular species. Each gene has two alleles, one of which results in a phenotype that is markedly different from the wild type. The unusual allele of gene A is inherited with the unusual allele of gene B or C about 50% of the time. However, the unusual alleles of genes B and C are inherited together 85.6% of the time. Which of the following describes what is happening? •The three genes are showing independent assortment. •Gene A is linked but genes B and C are not. •Gene A is located 14.4 map units from genes B and C. •Gene A is assorting independently of genes B and C, which are linked. •The three genes are linked.

Gene A is assorting independently of genes B and C, which are linked.

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

Half of their sons will have the recessive trait.

A woman is red-green color-blind. What can we conclude, if anything, about her father? •We have too little information to tell. •There is a 50% probability that he has normal vision. •He is red-green color-blind. •He has two Y chromosomes. •none of the above

He is red-green color-blind.

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

A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the results? •None of the females will have white eyes. •Fifty percent of the females will have red eyes. •Twenty-five percent of the females will have white eyes. •Twenty-five percent of the females will have red eyes. •None of the females will have red eyes.

None of the females will have white eyes.

_____ is usually less severe than _____, and _____ species have been observed in plants, fish, amphibians, and even mammals. •Polyploidy ... aneuploidy ... polyploid •Aneuploidy ... polyploidy ... aneuploid •Monosomy ... trisomy ... monosomic •Trisomy ... monosomy ... trisomic •Nondisjunction ... disjunction ... nondisjunctional

Polyploidy ... aneuploidy ... polyploid

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

She is XXX.

An inversion in a human chromosome often results in no demonstrable phenotypic effect in the individual. What else may occur? •All inverted chromosomes are deleted. •Some abnormal gametes may be formed. •The individual is more likely to get cancer. •There is an increased frequency of mutation. •There may be deletions later in life.

Some abnormal gametes may be formed.

X-linked genes differ from Y-linked genes in which of the following ways? •Only X-linked genes are technically sex-linked because Y-linked genes affect characteristics unrelated to sex. •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. •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. •Though most X-linked genes determine sex, Y-linked genes control for characters unrelated to sex.

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.

Gregor Mendel set up a dihybrid cross with one pea plant from the parental generation (P) producing round yellow peas and the other pea plant producing wrinkled green peas. The F2 generation included 315 plants producing round yellow peas, 108 with round green peas, 101 with wrinkled yellow peas, and 32 with wrinkled green peas. How would these results have differed if pea shape and pea color had been linked genes, located close together on the same chromosome? •The F2 generation would have included a higher percentage of pea plants producing round, yellow peas. •The F2 generation would have included a higher percentage of pea plants producing yellow peas. •The F2 generation would have included a lower percentage of pea plants producing wrinkled, green peas.

The F2 generation would have included a higher percentage of pea plants producing round, yellow peas.

Which of the following best describes the function of the XIST gene in X chromosome inactivation? •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.

Which of the following statements is true of linkage? •Crossing over occurs during prophase II of meiosis. •Linked genes are found on different chromosomes. •The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them. •The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%. •All of the traits that Mendel studied-seed color, pod shape, flower color, and others-are due to genes linked on the same chromosome.

The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.

Which of the following would result in genetic variation by way of new combinations of alleles? •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.

The chromosome theory of inheritance states that _____. •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.

When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result? •Other male-specific factors influence eye color in flies. •The gene involved is on an autosome, but only in males. •Other female-specific factors influence eye color in flies. •The gene involved is on the X chromosome. •The gene involved is on the Y chromosome.

The gene involved is on the X chromosome.

Which of the following is true of an X-linked gene, but not of a Y-linked gene? •Sister chromatids separate during mitosis. •The gene is present in both males and females. •It is only expressed in female offspring. •It does not segregate like other genes. •It is expressed in half of the cells of either male or female.

The gene is present in both males and females.

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? •Green-haired individuals have a higher prenatal mortality than black-haired individuals. •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 both of these traits are carried on the autosomes. •The genes for hair color and eye color are linked.

The genes for hair color and eye color are linked.

What is the reason that closely linked genes are typically inherited together? •Alleles are paired together during meiosis. •Genes align that way during metaphase I of meiosis. •The number of genes in a cell is greater than the number of chromosomes. •Chromosomes are unbreakable. •The likelihood of a crossover event between these two genes is low.

The likelihood of a crossover event between these two genes is low.

Select the correct statement(s) about sex determination in animals. • In all animals, males have the SRY gene and females lack this gene. • In all animals, males are XY and females are XX. • The mechanism of sex determination varies with different animal species.

The mechanism of sex determination varies with different animal species.

During meiosis, a defect occurs in a cell that results in the failure of microtubules, spindle fibers, to bind at the kinetochores, a protein structure on chromatids where the spindle fibers attach during cell division to pull sister chromatids apart. Which of the following is the most likely result of such a defect? •The resulting cells will not receive the correct number of chromosomes in the gametes, a condition known as aneuploidy. •Excessive cell divisions will occur resulting in cancerous tumors and an increase in the chromosome numbers known as polyploidy. •The defect will be bypassed in order to and ensure normal chromosome distribution in the new cells. •New microtubules with more effective binding capabilities to kinetochores will be synthesized to compensate for the defect.

The resulting cells will not receive the correct number of chromosomes in the gametes, a condition known as aneuploidy.

How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced? •Both of the characters are controlled by more than one gene. •The two genes are closely linked on the same chromosome. •The testcross was improperly performed. •Recombination did not occur in the cell during meiosis. •The two genes are linked but on different chromosomes.

The two genes are closely linked on the same chromosome.

What does a frequency of recombination of 50% indicate? •Independent assortment is hindered. •The two genes are likely to be located on different chromosomes. •Abnormal meiosis has occurred. •All of the offspring have combinations of traits that match one of the two parents. •The genes are located on sex chromosomes.

The two genes are likely to be located on different chromosomes.

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? •Sex-linked traits are never seen in girls. •The allele is carried on the Y chromosome. •Nondisjunction occurs in males but not in females. •To express an X-linked recessive allele, a female must have two copies of the allele. •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.

Of the following chromosomal abnormalities, which type is most likely to be viable in humans? Monosomy Trisomy Haploidy Triploidy

Trisomy

Which syndrome is characterized by the XO chromosome abnormality? •Turner syndrome •Down syndrome •Trisomy X •Klinefelter syndrome

Turner syndrome

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 _____. •a mutation •X chromosome inactivation •RNA splicing •an operon •a homeobox

X chromosome inactivation

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents? •XnXn and XnY •XnXn and XNY •XNXn and XNY •XNXN and XNY •XNXN and XnY

XNXn and XNY

Which of the following is the only known viable human monosomy? •XYY •XO •YO •XY •XXY

XO

SRY is best described in which of the following ways? •a gene present on the X chromosome that triggers female development •a gene region present on the Y chromosome that triggers male development •an autosomal gene that is required for the expression of genes on the X chromosome •a gene required for development, and males or females lacking the gene do not survive past early childhood •an autosomal gene that is required for the expression of genes on the Y chromosome

a gene region present on the Y chromosome that triggers male development

Which of the following is known as a Philadelphia chromosome? •a human chromosome 22 that has had a specific translocation •an animal chromosome found primarily in the mid-Atlantic area of the United States •an imprinted chromosome that always comes from the mother •a chromosome found not in the nucleus but in mitochondria •a human chromosome 9 that is found only in one type of cancer

a human chromosome 22 that has had a specific translocation

Normally, only female cats have the tortoiseshell phenotype because •a male inherits only one allele of the X-linked gene controlling hair color. •the Y chromosome has a gene blocking orange coloration. •multiple crossovers on the Y chromosome prevent orange pigment production. •only males can have Barr bodies. •the males die during embryonic development.

a male inherits only one allele of the X-linked gene controlling hair color.

What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction? •a deletion •a translocation •polyploidy •an inversion •a nondisjunction

an inversion

Cells that have a number of chromosomes different from the normal number for their species are known as _____. •aneuploid •diploid •polyploid •nanoploid •trisomy

aneuploid

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? •translocation •polyploidy •aneuploidy •duplication •monosomy

aneuploidy

Which of the following is a situation in which the chromosome number is either 2n+1 or 2n-1 ? •aneuploidy •methylation •polyploidy •inversion •gene linkage

aneuploidy

When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of _____ and results from _____. •aneuploidy ... nondisjunction of chromosome 21 during meiosis I •polyploidy ... occurrence of meiosis without cytokinesis •genomic imprint ... excessive methylation of either the paternal or maternal chromosome 21 •replication error ... an extra cycle of DNA synthesis during the S phase •none of the above

aneuploidy ... nondisjunction of chromosome 21 during meiosis I

Mutant tetraploid plants _____. •are usually sickly •are able to interbreed with their parents •have an odd number of chromosomes •are unable to interbreed with a diploid plant •unable to self-fertilize

are unable to interbreed with a diploid plant

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. •gray-bodied, normal-winged ... black-bodied, vestigial-winged •gray-bodied, vestigial-winged ... black-bodied, normal-winged •gray-bodied, normal-winged ... black-bodied, normal-winged •black-bodied, normal-winged ... black-bodied, vestigial-winged •black-bodied, normal-winged ... black-bodied, normal-winged

black-bodied, normal-winged ... black-bodied, vestigial-winged

Which type of chromosomal alteration is responsible for the cri du chat syndrome? •inversion •duplication •genetic imprinting •deletion •translocation

deletion

A nonreciprocal crossover causes which of the following products? •deletion only •deletion and duplication •duplication only •duplication and nondisjunction •nondisjunction

deletion and duplication

How are human mitochondria inherited? •from the father only •from the mother only •as linear DNA •without DNA •as an X-linked trait

from the mother only

The recombination frequency between two gene loci is _____. •dependent on the sex of the parent •greater as the distance between the two loci increases •greater as the distance between the two loci decreases •dependent on whether dominant or recessive alleles are carried at the two loci •equal to the size of the chromosome

greater as the distance between the two loci increases

What can we observe in order to visualize Mendel's Law of Segregation? •the replication of DNA •the behavior of sex-linked genes •sister chromatids separating during mitosis •homologous chromosomes separating during meiosis I •homologous chromosomes separating during meiosis II

homologous chromosomes separating during meiosis I

In general, the frequency with which crossing over occurs between two linked genes depends on what? •the characters the genes code for •whether the genes are dominant or recessive •whether the genes are on the X or some other chromosome •how far apart they are on the chromosome •the phase of meiosis in which the crossing over occurs

how far apart they are on the chromosome

Most polyploid plants arise as a result of _____. •self-fertilization •a mutation of gamete formation •meiosis •mitosis •hybridization

hybridization

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 _____. •inversion •translocation •transduction •transformation •duplication

inversion

Males are more often affected by sex-linked traits than females because •mutations on the Y chromosome often worsen the effects of X-linked mutations. •males are hemizygous for the X chromosome. •male hormones such as testerone often alter the affects of mutations on the X chromosome. •female hormones such as estrogen often compensate for the effects of mutations on the X chromosome. •X chromosomes in males generally have more mutations than X chromosomes in females.

males are hemizygous for the X chromosome.

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

map units do not necessarily correlate to physical distances along the chromosome

Individuals with an extra X chromosome _____. •may have subnormal intelligence or be at risk for learning disabilities •have distinguishing physical features •are generally sterile •are always female •None of the listed responses is correct.

may have subnormal intelligence or be at risk for learning disabilities

Inheritance patterns cannot always be explained by Mendel's models of inheritance. If a pair of homologous chromosomes fails to separate during meiosis I, select the choice that shows the chromosome number of the four resulting gametes with respect to the normal haploid number (n)? • n+1; n-1; n; n • n+1; n+1; n-1; n-1 • n+1; n+1; n; n • n+1; n-1; n-1; n-1

n+1; n+1; n-1; n-1

During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____. •cellular sterility •meiotic failure •gametic infertility •nondisjunction •sticky chiasmata

nondisjunction

What is the source of the extra chromosome 21 in an individual with Down syndrome? •duplication of the chromosome •nondisjunction in the mother only •nondisjunction in the father only •It is impossible to detect with current technology. •nondisjunction or translocation in either parent

nondisjunction or translocation in either parent

A linkage map _____. •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 •predicts the probability that you will have a male or female child

orders genes on a chromosome based on recombination frequencies

Which of these terms applies to an organism with extra sets of chromosomes? •monosomy •haploid •trisomy •polyploid •diploid

polyploid

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 _____. •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

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

the most common phenotype thought to be found in the natural population

In an X-linked, or sex-linked, trait, it is the contribution of _____ that determines whether a son will display the trait. •the mother •the father •the paternal grandmother •the paternal grandfather •none of the above

the mother

In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male? •orange females; orange males •orange females; black males •black females; orange males •tortoiseshell females; tortoiseshell males •tortoiseshell females; black males

tortoiseshell females; black males

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

translocation occurred

Sex determination in mammals is due to the SRY region of the Y chromosome. An abnormality of this region could allow which of the following to have a male phenotype? •a person with one normal and one shortened (deleted) X •translocation of SRY to an autosome of a 46, XX individual •Down syndrome, 46, XX •Turner syndrome, 45, X •a person with an extra X chromosome

translocation of SRY to an autosome of a 46, XX individual

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 _____. •linked •unlinked •similar in DNA sequence •mutated •imprinted

unlinked

What name is given to the most common phenotype in a natural population? •autosome •wild type •locus •mutant phenotype •genotype

wild type