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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?
A. Males would display this disorder with greater frequency than females.
B. Males and females would display this disorder with equal frequency.
C. Females would display this disorder with greater frequency than males.

C

Select all that apply.
A. In all animals, males have the SRY gene and females lack this gene.
B. In all animals, males are XY and females are XX.
C. The mechanism of sex determination varies with different animal species.

C

Which of these descriptions of the behavior of chromosomes during meiosis explains Mendel's law of segregation?
A. The two alleles for each gene separate as homologous chromosomes move apart during anaphase I.
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. Sister chromatids separate during anaphase II.

A

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. 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. Sister chromatids separate during anaphase II.

B

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?
A. The F2 generation would have included a higher percentage of pea plants producing round, yellow peas.
B. The F2 generation would have included a higher percentage of pea plants producing yellow peas.
C. The F2 generation would have included a lower percentage of pea plants producing wrinkled, green peas.

A

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? Express your answer as a percentage.

17

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 only affect girls.
C. The disorder would always be inherited from the father.
D. The disorder would always be inherited from the mother.

D

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

A

What name is given to the most common phenotype in a natural population?
A. autosome
B. wild type
C. locus
D. genotype
E. mutant phenotype

B

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?
A. Drosophila genes have, on average, four different alleles.
B. Drosophila genes cluster into four distinct groups of linked genes.
C. The entire Drosophila genome has approximately 400 map units.
D. The overall number of genes in Drosophila is a multiple of four.
E. There are four major functional classes of genes in Drosophila.

B

Which of the following is the meaning of the chromosome theory of inheritance as expressed in the early 20th century?
A. Individuals inherit particular chromosomes attached to genes.
B. Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis.
C. Natural selection acts on certain chromosome arrays rather than on genes.
D. Homologous chromosomes give rise to some genes and crossover chromosomes to other genes.
E. No more than a single pair of chromosomes can be found in a healthy normal cell.

B

A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following describes her expected phenotype?
A. healthy female of slightly above-average height
B. enlarged genital structures
C. sterile female
D. masculine characteristics such as facial hair
E. excessive emotional instability

A

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

D

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. translocation of SRY to an autosome of a 46, XX individual
B. a person with an extra X chromosome
C. Down syndrome, 46, XX
D. Turner syndrome, 45, X
E. a person with one normal and one shortened (deleted) X

A

All female mammals have one active X chromosome per cell instead of two. What causes this?
A. attachment of methyl (CH3) groups to the X chromosome that will remain active
B. crossing over between the XIST gene on one X chromosome and a related gene on an autosome
C. activation of the XIST gene on the X chromosome that will become the Barr body
D. inactivation of the XIST gene on the X chromosome derived from the male parent
E. activation of the BARR gene on one X chromosome, which then becomes inactive

C

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

A

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

B

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

E

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

B

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

C

Which statement about recombination between linked genes is correct?
A. Recombination must occur or genes will not assort independently.
B. Without recombination there would be an insufficient number of gametes.
C. Recombination is a requirement for independent assortment.
D. The forces on the cell during meiosis II always result in recombination.
E. New allele combinations may result in differential reproductive success.

E

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?
A. The frequency of crossing over varies along the length of the chromosome.
B. The relationship between recombination frequency and map units is different in every individual.
C. Physical distances between genes change during the course of the cell cycle.
D. The gene order on the chromosomes is slightly different in every individual.
E. Linkage map distances are identical between males and females.

A

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 14.4% of the time. Which of the following describes what is happening?
A. The three genes are linked.
B. Gene A is located 14.4 map units from genes B and C.
C. Gene A is linked but genes B and C are not.
D. Gene A is assorting independently of genes B and C, which are linked.
E. The three genes are showing independent assortment

D

What is the greatest benefit of having used a testcross for this experiment?
A. The homozygous recessive parents are obvious to the naked eye.
B. The homozygous parents are the only ones whose crossovers make a difference.
C. The phenotypes of the progeny reveal the allelic content of the gamete from the heterozygous parent.
D. All of the progeny will be heterozygous.
E. The homozygous recessive parents will be unable to cross over.

C

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

E

Which of the following results in a situation in which the chromosome number is either 2n+1 or 2n-1 ?
A. inversion
B. methylation
C. polyploidy
D. gene linkage
E. aneuploidy

E

A nonreciprocal crossover causes which of the following products?
A. deletion and duplication
B. duplication only
C. duplication and nondisjunction
D. nondisjunction
E. deletion only

A

A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?
A. His sperm will be sterile and the couple might consider adoption.
B. All will carry the same translocation as the father.
C. 1/4 will be normal, 1/4 will have the translocation, and 1/2 will have duplications and deletions.
D. None will carry the translocation since abnormal sperm will die.
E. 1/2 will be normal and the rest will have the father's translocation

C

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

D

Down syndrome has a frequency in the U.S. population of ~ 1/700 live births. In which of the following groups would you expect this frequency to be significantly higher?
A. people in Latin or South America
B. the Inuit and other peoples in very cold habitats
C. very small population groups
D. people living in equatorial areas of the world
E. No groups have such higher frequency.

E

A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?
A. The mother had a chromosomal duplication.
B. One member of the couple underwent nondisjunction in gamete production.
C. One member of the couple carried a translocation.
D. The woman inherited this tendency from her parents.
E. One member of the couple underwent nondisjunction in somatic cell production.

B

What is a syndrome?
A. a group of traits, all of which must be present if an aneuploidy is to be diagnosed
B. a characteristic that only appears in conjunction with one specific aneuploidy
C. a group of traits typically found in conjunction with a particular chromosomal aberration or gene mutation
D. a characteristic trait usually given the discoverer's name
E. a characteristic facial appearance

C

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

D

Which of the following is true of aneuploidies in general?
A. 45 X is the only known human live-born monosomy.
B. Of all human aneuploidies, only Down syndrome is associated with mental retardation.
C. An aneuploidy resulting in the deletion of a chromosome segment is less serious than a duplication.
D. Some human aneuploidies have selective advantage in some environments.
E. A monosomy is more frequent than a trisomy.

A

If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, what will be the result at the completion of meiosis?
A. Two of the four gametes descended from cell X will be haploid, and two will be diploid.
B. All the gametes descended from cell X will be diploid.
C. 1/4 of the gametes descended from cell X will be n + 1, 1/4 will be n - 1, and 1/2 will be n.
D. There will be three extra gametes.
E. Half of the gametes descended from cell X will be n + 1, and half will be n - 1.

C

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. aneuploidy
B. genomic imprinting
C. sex linkage
D. polyploidy
E. extranuclear inheritance

B

How are human mitochondria inherited?
A. without DNA
B. from the mother only
C. as linear DNA
D. from the father only
E. as an X-linked trait

B

Genomic imprinting is generally due to the addition of methyl (-CH3) groups to C nucleotides in order to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following must be true?
A. Methylation must be reversible in ovarian and testicular cells.
B. Methylation of this kind must occur more in males than in females.
C. Genes required for early development stages must not be imprinted.
D. Methylation of C is permanent in a gene.
E. The imprints are transmitted only to gamete-producing cells.

A

Correns described that the inheritance of variegated color on the leaves of certain plants was determined by the maternal parent only. What phenomenon does this describe?
A. mitochondrial inheritance
B. genomic imprinting
C. chloroplast inheritance
D. infectious inheritance
E. sex-linkage

C

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