question

Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1? a) gene linkage b) methylation c) aneuploidy d) inversion e) polyploidy

answer

c) aneuploidy

question

What can we observe to visualize Mendel's Law of Segregation? a) the replication of DNA b) homologous chromosomes separating during meiosis I c) sister chromatids separating during mitosis d) homologous chromosomes separating during meiosis II e) the behavior of sex-linked genes

answer

b) homologous chromosomes separating during meiosis I

question

What name is given to the most common phenotype in a natural population? a) mutant phenotype b) genotype c) autosome d) locus e) wild type

answer

e) wild type

question

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

answer

a) None of the females will have white eyes

question

Eye color exhibits sex-linked inheritance 1. If there were 100 female offspring, ______ would have red eyes and ______ would have white eyes. 2. If there were 100 male offspring, ______ would have red eyes and _______ would have white eyes.

answer

1. 100, 0 2. 0, 100

question

Eye color exhibits autosomal (non-sex-linked) inheritance 3. If there were 100 female offspring, ____ would have red eyes and _____ would have white eyes. 4. If there were 100 male offspring, _____ would have red eyes and ____ would have white eyes.

answer

3. 100, 0 4. 100, 0

question

*Bob has a genetic condition that affects his skin. * Bob's wife, Eleanor, has normal skin. No one in Eleanor's family has ever had the skin condition. * Bob and Eleanor have a large family. Of their eleven children, al six of their sons have normal skin, but all of their daughters have the same skin condition as Bob. Based on Bob and Eleanor's family history, what inheritance pattern does the skin condition most likely follow? a) X-linked recessive b) autosomal dominant c) Y-linked d) X-linked dominant e) autosomal recessive

answer

d) X-linked dominant

question

Red-green color blindness is due to an X-linked recessive allele in humans. A widow's peak is due to an autosomal dominant allele. Consider the following family history: * A man with a widow's peak and normal color vision marries a color-blind woman with a straight hairline. * The man's father had a straight hairline, as did both of the woman's parents. Use the family history to make predictions about the couple's children. Suppose the couple had a daughter with normal color vision and a widow's peak. What is the chance that she is heterozygous for both genes?

answer

1

question

In humans, what determines the sex of offspring and why? a) The chromosome contribution from both parents determines sex because the offspring uses all the parents' chromosomes. b) The female gamete determines sex because only the female gamete provides cytoplasm to the zygote. c) The male determines sex because the sperm can fertilize either a female egg or a male egg. d) The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome. e) The female gamete determines sex because only the female gametes can have one of the two functional sex chromosomes.

answer

d) The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome.

question

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

answer

c) The gene is present in both males and females.

question

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

answer

c) how far apart they are on the chromosome

question

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

answer

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

question

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

answer

d) All three answers are correct

question

Which syndrome is characterized by the XO chromosome abnormality? a) Klinefelter syndrome b) Trisomy X c) Turner syndrome d) Down syndrome

answer

c) Turner syndrome

question

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

answer

c) A triploid cell

question

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

answer

c) Trisomy

question

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) A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same of the cell. b) No error occurred; these are normal gametes c) A nondisjunction error occurred in meiosis I, in which both members of all homologous pairs migrated to the same pole of the cell. d) A non disjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

answer

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

question

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) A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell. b) No error occurred; these these are normal gametes. c) A nondisjunction error occurred in meiosis I, in which both members of all homologous pairs migrated to the same pole of the cell. d) A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

answer

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

question

If 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) A nondisjunction error occurred in meiosis I, in which both members of all homologous pairs migrated to the same pole of the cell. b) No error occurred; these are normal gametes. c) A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell. d) A non disjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.

answer

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

question

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) a translocation b) an inversion c) a nondisjunction d) a deletion e) polyploidy

answer

b) an inversion

question

What phenomenon occurs when a particular allele will either be expressed or silenced, depending on whether it is inherited from a male or a female? a) sex linkage b) aneuploidy c) genomic imprinting d) polyploidy e) extranuclear inheritance

answer

c) genomic imprinting

question

How are human mitochondria inherited? a) as an X-linked trait b) without DNA c) as linear DNA d) from the father only e) from the mother only

answer

e) from the mother only

question

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?

answer

1/2

question

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 a couple has four sons, what is the probability that all four will be born with hemophilia?

answer

1/16

question

A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild-type 778 black-vestigial 785 black-normal 158 gray-vestigial 162 What is the recombination frequency between these genes for body color and wing size?

answer

17%

question

What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene? a) The disorder would only affect boys. b) The disorder would always be inherited from the mother. c) The disorder would only affect girls. d) The disorder would always be inherited from the father.

answer

b) The disorder would always be inherited from the mother.

question

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

answer

1/4

question

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

answer

1/2

question

A wild-type fruit fly (heterozygous for gray body and red eyes) is mated with a black fruit fly with purple eyes. The offspring are: wild-type 721 black-purple 751 gray-purple 49 black-red 45 What is the recombination frequency between these genes for body color and eye color?

answer

6%

question

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?

answer

50%

question

Two genes of a flower, on controlling blue (B) versus white (b) petals and the other controlling round (R) versus oval (r) stamens, are linked and are 10 map units apart. You cross a homozygous blue-oval plant with a homozygous white-round plant. The resulting F? progeny are crossed with homozygous white-oval plants, and 1,000 F? progeny are obtained. How many F? plants of each of the four phenotypes do you expect? ____ blue-oval:____white-round:____blue-round:_____white-oval

answer

450:450:50:50

question

For tall heterozygotes with antennae, the offspring are: tall-antennae 46 dwarf-antennae 7 dwarf-no antennae 42 tall-no antennae 5 Calculate the recombination frequency between T and A.

answer

12%

question

For heterozygotes with antennae and an upturned snout, the offspring are: antennae-upturned snout 47 antennae-downturned snout 2 no-antennae-downturned snout 48 no antennae-upturned snout 3 Calculate the recombination frequency between A and S.

answer

5%

question

Scientists do a further testcross using a heterozygote for height and nose morphology. The offspring are: tall-upturned snout 40 dwarf-upturned snout 9 dwarf-downturned snout 42 tall-downturned snout 9 Calculate the recombination frequency between T and S.

answer

18%

question

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel's law of segregation? a) Sister chromatids separate during anaphase II. b) The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs. c) The two alleles for each gene separate as homologous chromosomes move apart during anaphase I.

answer

c) The two alleles for each gene separate as homologous chromosomes move apart during anaphase I.

question

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel's law of independent assortment? a) The two alleles for each gene separate as homologous chromosomes move apart during anaphase I. b) Sister chromatids separate during anaphase II. c) The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs.

answer

c) The arrangement of each pair of homologous chromosomes on the metaphase plate during metaphase I is random with respect to the arrangements of other pairs.

question

The chromosome theory of inheritance states that _____. a) genes occupy specific positions on chromosomes b) homologous chromosomes segregate from each other during meiosis c) chromosomes assort independently during meiosis d) The first and second answers are correct. e) The first, second, and third answers are correct.

answer

e) The first, second, and third answers are correct.

question

Why did Morgan choose Drosophila for his genetics experiments? a) They have a long generation time. b) A single mating can produce many offspring. c) They have a large number of chromosomes. d) Drosophila chromosomes can be easily distinguishable under a light microscope. e) Both the second and fourth answers are correct.

answer

e) Both the second and fourth answers are correct.

question

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

answer

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

question

Which of the following results of Thomas Hunt Morgan's experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics? a) The F1 flies were crossed with each other, and the F2 progeny included red-eyed and white-eyed flies in a 3:1 ratio. b) The mutant allele (white eyes) was recessive. c) Among the F2 progeny, only males had white eyes. All of the females had red eyes. d) In the parental cross, a white-eyed male was crossed with a red-eyed female. The F1 progeny all had red eyes. e) all of the above

answer

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

question

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

answer

c) 0%

question

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

answer

a) the mother

question

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? a) None of their sons will have the recessive trait. b) Half of their sons will have the recessive trait. c) All of their daughters will be heterozygous. d) All of their sons will have the recessive trait. e) none of the above

answer

b) Half of their sons will have the recessive trait.

question

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? a) 75% b) 100% c) 25% d) 0% e) 50%

answer

e) 50%

question

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

answer

d) He is red-green color-blind.

question

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? a) 100% b) 75% c) 0% d) 50% e) 25%

answer

c) 0%

question

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

answer

a) To express an X-linked recessive allele, a female must have two copies of the allele.

question

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

answer

c) 50%

question

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? a) Either her mother was a carrier or her father had a dominant allele. b) Both her mother and her father had hemophilia. c) Either her mother was a carrier or her father had hemophilia. d) Either her mother was homozygous dominant or her father had hemophilia. e) none of the above

answer

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

question

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

answer

a) Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females.

question

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) RNA splicing b) a mutation c) a homeobox d) an operon e) X chromosome inactivation

answer

e) X chromosome inactivation

question

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? a) She is XXXX. b) She is XXY, but the Y chromosome lacks the SRY gene. c) She is XXX. d) She is XX. e) none of the above

answer

c) She is XXX.

question

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

answer

e) 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.

question

Which of the following best describes the function of the XIST gene in X chromosome inactivation? a) The XIST gene codes for an enzyme that methylates DNA on the X chromosome being inactivated. b) 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. c) 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. d) 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. e) The first and second listed responses are correct.

answer

b) 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.

question

If two genes are linked, _____. a) they assort independently b) they are on different chromosomes c) they code for the same protein d) they are on the same chromosome e) they are on sex chromosomes

answer

d) they are on the same chromosome

question

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

answer

b) The genes for hair color and eye color are linked.

question

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. a) gray-bodied, vestigial-winged ... black-bodied, normal-winged b) gray-bodied, normal-winged ... black-bodied, vestigial-winged c) black-bodied, normal-winged ... black-bodied, vestigial-winged d) black-bodied, normal-winged ... black-bodied, normal-winged e) gray-bodied, normal-winged ... black-bodied, normal-winged

answer

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

question

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 _____. a) linked b) imprinted c) mutated d) similar in DNA sequence e) unlinked

answer

e) unlinked

question

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

answer

b) greater as the distance between the two loci increases

question

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? a) ABCD b) ABDC c) ACDB d) ACBD e) ADBC

answer

d) ACBD

question

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? a) 7% b) approximately 14% c) approximately 17% d) 30% e) 86%

answer

b) approximately 14%

question

A linkage map _____. a) shows the ordering and exact spacing of genes on a chromosome b) orders genes on a chromosome based on their location with respect to a stained band c) orders genes on a chromosome based on recombination frequencies d) predicts the probability that you will have a male or female child e) can be constructed only for sex chromosomes

answer

c) orders genes on a chromosome based on recombination frequencies

question

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

answer

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

question

Which of the following would result in genetic variation by way of new combinations of alleles? a) independent alignment of homologous chromosomes during meiosis I b) the exchange of alleles between homologous chromosomes during meiosis I c) random fertilization increasing the number of possible allele combinations in an individual d) The first and second responses are correct. e) The first three responses are correct.

answer

e) The first three responses are correct.

question

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 _____. a) 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 b) 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 c) 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 d) help offset the financial cost of treating and correcting this disorder e) The second and third listed responses are correct.

answer

b) 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

question

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

answer

c) may have subnormal intelligence or be at risk for learning disabilities

question

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

answer

a) nondisjunction

question

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? a) monosomy b) aneuploidy c) polyploidy d) translocation e) duplication

answer

b) aneuploidy

question

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

answer

d) aneuploid

question

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

answer

c) Polyploidy ... aneuploidy ... polyploid

question

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

answer

b) translocation occurred

question

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 _____. a) transformation b) duplication c) inversion d) transduction e) translocation

answer

c) inversion

question

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

answer

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

question

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

answer

a) aneuploidy ... nondisjunction of chromosome 21 during meiosis I

question

A person with two X chromosomes and one Y chromosome would appear to be _____. a) both male and female b) neither male nor female c) male d) female e) any of the listed responses, depending on the number of other chromosomes

answer

c) male

question

Which of the following is the only known viable human monosomy? a) XY b) XO c) XYY d) YO e) XXY

answer

b) XO

question

Which type of chromosomal alteration is responsible for the cri du chat syndrome? a) duplication b) deletion c) translocation d) inversion e) genetic imprinting

answer

b) deletion

question

What appears to be the mechanism for genomic imprinting? a) DNA methylation that silences particular genes b) crossing over c) DNA methylation that activates particular genes d) nondisjunction e) both the first and third listed responses

answer

e) both the first and third listed responses

question

Genomic imprinting in mammals appears to affect primarily genes involved in _____. a) function of the nervous system b) embryonic development c) sex determination d) vision e) digestion

answer

b) embryonic development

question

Both chloroplasts and mitochondria _____. a) have linear DNA b) display a Mendelian pattern of inheritance c) are inherited from both parents d) carry extranuclear genes e) are found within the nucleus

answer

d) carry extranuclear genes

question

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

answer

d) Fathers with the disorder pass it on to all their children, but mothers with the disorder do not pass it along.

question

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? a) Anyone from the same family will have nearly identical mitochondrial DNA. b) one of the couple's other children c) the husband's d) the husband's mother e) either the husband's or the wife's

answer

b) one of the couple's other children

question

X-linked genes

answer

a gene located on the X chromosome; such genes show a distinctive pattern of inheritance

question

aneuploidy

answer

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number

question

Down syndrome

answer

A human genetic disease usually caused by the presence of an extra chromosome 21; characterized by developmental delays and heart and other defects that are generally treatable or non-life-threatening

question

trisomic

answer

referring to a diploid cell that has three copies of a particular chromosome instead of the normal two

question

deletion

answer

1) a deficiency in a chromosome resulting from the loss of a fragment through breakage. 2) a mutational loss of one or more nucleotide pairs from a gene

question

hemophilia

answer

a human genetic disease caused by a sex-linked recessive allele resulting in the absence of one or more blood-clotting proteins; characterized by excessive bleeding following injury.

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linkage map

answer

a genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes

question

recombinant type

answer

an offspring whose phenotype differs from that of the true-breeding P generation parents; also refers to the phenotype itself

question

genetic map

answer

an ordered list of genetic loci (genes or other genetic markers) along a chromosome

question

genomic imprinting

answer

a phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent

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genetic recombination

answer

general term for the production of offspring with combinations of traits that differ from those found in either parent

question

chromosome theory of inheritance

answer

a basic principle in biology stating that genes are located at specific positions (loci) on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns

question

cytogenetic map

answer

a map of a chromosome that locates genes with respect to chromosomal features distinguishable in a microscope

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linked genes

answer

genes located close enough together on a chromosome that they tend to be inherited together

question

crossing over

answer

the reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis

question

nondisjunction

answer

an error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other

question

map unit

answer

a unit of measurement of the distance between genes. one map unit is equivalent to a 1% recombination frequency

question

polyploidy

answer

a chromosomal alternation in which the organism possesses more than two complete chromosome sets. it is the result of an accident of cell division

question

translocation

answer

1) an aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome. 2) during protein synthesis, the third stage in the elongation cycle, when the RNA carrying the growing polypetide moves from the A site to the P site on the ribosome. 3) the transport of organic nutrients in the phloem of vascular plants

question

inversion

answer

an aberration in chromosome structure resulting from reattachment of a chromosomal fragment in a reverse orientation to the chromosome from which it originated

question

wild type

answer

the phenotype most commonly observed in natural populations; also refers to the individual with that phenotype

question

parental type

answer

an offspring with a phenotype that matches one of the true-breeding parental (P generation) phenotypes; also refers to the phenotype itself

question

Barr body

answer

a dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X chromosome

question

sex-linked gene

answer

a gene located on either sex chromosome. most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome

question

monosomic

answer

referring to a diploid cell that has only one copy of a particular chromosome instead of the normal two

question

duplication

answer

an aberration in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated

question

Duchenne muscular dystrophy

answer

a human genetic disease caused by a sex-linked recessive allele; characterized by progressive weakening and a loss of muscle tissue

question

What is the chromosome theory of inheritance?

answer

The chromosome theory of inheritance is a basic principle in biology stating that genes are located at specific positions (loci) on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.

question

Explain the law of segregation.

answer

The law of segregation states that the two alleles for each gene separate during gamete formation.

question

Explain the law of independent assortment.

answer

The law of independent assortment states that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes.

question

What is the SRY gene? Where is it found, and what does it do?

answer

SRY refers to the Sex determining Region of Y, a gene found on the Y chromosome that is required for the development of testes.

question

What is the definition of a sex-linked gene?

answer

A gene located on either sex chromosome. Most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome.

question

In humans, how has that term been historically modified?

answer

Typically, the sex-linked traits are actually X-linked genes.

question

What is a Barr body? Why do human females show a Barr body in their cells?

answer

A Barr body is a dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X chromosome. Female mammals, including humans, inherit two X chromosomes—twice the number inherited by males; females show a Barr body in their cells so that the cells of females and males have the same effective dose (one copy) of most X-linked genes.

question

X inactivation maintains the proper gene dosage. How is the X chromosome inactivated?

answer

The selection of which X chromosome will form the Barr body occurs randomly and independently in each embryonic cell present at the time of X inactivation.

question

What are linked genes? Do linked genes sort independently?

answer

Linked genes are genes located close enough together on a chromosome that they tend to be inherited together. These genes do not sort independently, but rather are transmitted as a unit. It is important to note that as Morgan's experiments illustrated, some mechanism (later discovered to be "crossing over") occasionally breaks the linkage between specific alleles of genes on the same chromosome.

question

When does crossing over occur?

answer

Prophase I

question

Although you inherited one chromosome of each pair from your mother and your father, you have inherited a group of genes from your mother only. What genes are these?

answer

Mitochondrial DNA

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