Deck 12: The Chromosomal Basis of Inheritance

Question 1

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?

A)tortoiseshell females;tortoiseshell males
B)black females;orange males
C)orange females;orange males
D)tortoiseshell females;black males

Answer 1

D

Question 2

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome.The patients have muscles that weaken over time because they have absent or decreased dystrophin,a muscle protein.They rarely live past their 20s.How likely is it for a woman to have this condition?

A)Women can never have this condition.
B)One-half of the daughters of an affected man would have this condition.
C)One-fourth of the daughters of an affected father and a carrier mother could have this condition.
D)Very rarely: it is rare that an affected male would mate with a carrier female.

Answer 2

D

Question 3

What does a frequency of recombination of 50% between two genes indicate?

A)The two genes are likely to be located on different chromosomes.
B)All of the offspring have combinations of traits that match one of the two parents.
C)The genes are located on sex chromosomes.
D)Independent assortment of the two genes will not occur.

Answer 3

A

Question 4

What is the result of the activation of the XIST gene in mammals?

A)the inactivation of one of the X chromosomes,which then becomes a Barr body in females
B)activation of the SRY gene that results in the development of male sexual characteristics
C)the activation of genes on both X chromosomes in females
D)the expression of sex-linked traits in males

Question 5

In humans,clear sex differentiation occurs not at fertilization but after the second month of gestation.What is the first event of this differentiation?

A)formation of testosterone in male embryos
B)formation of estrogens in female embryos
C)anatomical differentiation of a penis in male embryos
D)activation of the SRY gene in male embryos and development of testes

Question 6

Normally,only female cats have the tortoiseshell phenotype because

A)the males die during embryonic development.
B)a male inherits only one allele of the X-linked gene controlling hair color.
C)the Y chromosome has a gene blocking orange coloration.
D)only males can have Barr bodies.

Question 7

Which of the following events causes recombination between linked genes to occur?

A)Mutation that causes one homolog to be different from the other homolog.
B)Independent assortment of the genes.
C)Crossovers between the genes results in chromosomal exchange.
D)Nonrecombinant chromosomes break and then re-join with one another.

Question 8

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?

A)The gene involved is on the Y chromosome.
B)The gene involved is on the X chromosome.
C)The gene involved is on an autosome,but only in males.
D)Eye color in flies is a multifactorial trait.

Question 9

Sex determination in mammals is due to the SRY gene on the Y chromosome.An abnormality of this region could allow which of the following individuals to have a male phenotype?

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

Question 10

Cinnabar eyes is a sex-linked recessive characteristic in fruit flies in which the eyes of the individual are lighter in color than the normal wild-type red color.If a female having cinnabar eyes is crossed with a wild-type male,what percentage of the F₁ males will have cinnabar eyes?

A)0%
B)25%
C)50%
D)100%

Question 11

One map unit is equivalent to which of the following values?

A)the physical distance between two linked genes
B)1% frequency of recombination between two genes
C)1 nanometer of distance between two genes
D)the distance between a pair of homologous chromosomes

Question 12

Which of the following statements describes the chromosome theory of inheritance as expressed in the early twentieth 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)Homologous chromosomes give rise to some genes and crossover chromosomes to other genes.
D)No more than a single pair of chromosomes can be found in a healthy normal cell.

Question 13

What is the reason that closely linked genes are typically inherited together?

A)The likelihood of a crossover event between these two genes is low.
B)The number of genes in a cell is greater than the number of chromosomes.
C)Chromosomes are unbreakable.
D)Alleles are paired together during meiosis..

Question 14

How does the recombination of linked genes contribute to natural selection?

A)It reduces genetic variability in a sexually reproducing species.
B)It eliminates specific alleles in a population.
C)It maintains genetic variability in a species.
D)It increases the number of alleles associated with a specific gene.

Question 15

Which of the following statements best describes the SRY gene?

A)It is a gene present on the X chromosome that triggers female development.
B)It is an autosomal gene that is required for the expression of genes on the Y chromosome.
C)It is a gene region present on the Y chromosome that triggers male development.
D)It is an autosomal gene that is required for the expression of genes on the X chromosome.

Question 16

Males are more often affected by sex-linked traits than females because

A)sex-linked traits are located on autosomes that affect males more severely than females.
B)the presence of a Y chromosome often worsens the effects of X-linked mutations.
C)X chromosomes in males generally have more mutations than X chromosomes in females.
D)males are hemizygous for the X chromosome.

Question 17

Two autosomal genes have a recombination frequency of 16%.Which of the following conclusions can be drawn regarding these genes?

A)The two genes are closely linked on the same chromosome.
B)The two genes are linked but on different chromosomes.
C)Recombination between these two genes cannot occur in the cell during meiosis.
D)The genes are located on the X chromosome.

Question 18

Which of the following statements correctly describes gene linkage?

A)The closer two genes are on a chromosome,the lower the probability that a crossover will occur between them.
B)The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 100%.
C)Linked genes always assort independently.
D)Linked genes are found on different chromosomes.

Question 19

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.

Question 20

Red-green color blindness is a sex-linked recessive trait in humans.The normal,dominant allele is symbolized with X^N,and the recessive allele is symbolized with Xⁿ.Two people with normal color vision have a color-blind son.What are the genotypes of these parents?

A)X^NXⁿ and XⁿY
B)XⁿXⁿ and X^NY
C)X^NX^N and XⁿY
D)X^NX^N and X^NY
E)X^NXⁿ and X^NY

Question 21

A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves,due to an allele (a)of gene A;a feathered stem,due to an allele (b)of gene B;and hollow roots,due to an allele (c)of gene C.The three genes are linked and recombine.
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and was able to identify progeny of the phenotypic distribution (+ = wild type)shown in the figure below.
The greatest distance among the three genes is between a and c.What does this mean?

A)Gene c is between a and b.
B)Genes are in the order: a-b-c.
C)Gene a is not recombining with c.
D)Gene a is between b and c.

Question 22

Which of the following types of diseases is associated with the Philadelphia chromosome?

A)chronic myelogenous leukemia
B)Down syndrome
C)Klinefetler syndrome
D)heart disease

Question 23

One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome.What is this alteration called?

A)deletion
B)transversion
C)inversion
D)translocation

Question 24

The figure below shows a map of four genes on a chromosome.

A)A and W
B)W and E
C)E and G
D)A and G

Question 25

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 woman inherited this tendency from her parents.
B)One member of the couple carried a translocation.
C)Nondisjunction occurred in one member of the couple during somatic cell production.
D)Nondisjunction occurred in one member of the couple during gamete production.

Question 26

A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves,due to an allele (a)of gene A;a feathered stem,due to an allele (b)of gene B;and hollow roots,due to an allele (c)of gene C.The three genes are linked and recombine.
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and was able to identify progeny of the phenotypic distribution (+ = wild type)shown in the figure below.
In which progeny phenotypes has there been recombination between genes A and B? The parent phenotypes are 4 and 8.

A)1,2,5,and 6
B)1,3,6,and 7
C)2,4,5,and 8
D)2,3,5,and 7

Question 27

A woman is found to have 47 chromosomes,including three X chromosomes.Which of the following describes her expected phenotype?

A)masculine characteristics such as facial hair
B)enlarged genital structures
C)healthy female of slightly above-average height
D)sterile female

Question 28

Which of the following statements correctly describes aneuploid conditions?

A)A monosomy is more frequent than a trisomy.
B)Monosomy X is the only known viable human monosomy.
C)Of all human aneuploidies,only Down syndrome is associated with developmental delays or subnormal intelligence.
D)An aneuploidy resulting in the deletion of a chromosome segment is less serious than a duplication.

Question 29

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)All the gametes descended from cell X will be diploid.
B)Half of the gametes descended from cell X will be n + 1,and half will be n - 1.
C)One-fourth of the gametes descended from cell X will be n + 1,1/4 will be n - 1,and 1/2 will be n.
D)All of the gametes will have the normal number of chromosomes.

Question 30

In a series of mapping experiments,the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure above.Based on these frequencies,what is the order of these genes on a chromosome map?

A)rb-cn-vg-b
B)vg-b-rb-cn
C)cn-rb-b-vg
D)b-rb-cn-vg

Question 31

Which of the following statements regarding Down syndrome is correct?

A)Down syndrome is the result of a chromosomal duplication.
B)The age of the mother has nothing to do with the frequency of births of children with Down syndrome.
C)The frequency decreases with the age of the mother.
D)The frequency increases with the age of the mother.

Question 32

What evidence did Alfred Sturtevant use to support his conclusion that Drosophila have four pairs of chromosomes?

A)All of the genes he identified had a recombination frequency of 50%.
B)Drosophila genes cluster into four distinct groups of linked genes.
C)The overall number of genes in Drosophila is a multiple of four.
D)All of the genes he identified had recombination frequencies of less than 50%.

Question 33

A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves,due to an allele (a)of gene A;a feathered stem,due to an allele (b)of gene B;and hollow roots,due to an allele (c)of gene C.The three genes are linked and recombine.
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and was able to identify progeny of the phenotypic distribution (+ = wild type)shown in the figure below.
If recombination frequency is equal to distance in map units,what is the approximate distance between genes A and B?

A)1)5 map units
B)3 map units
C)6 map units
D)15 map units

Question 34

Which of the following results might be caused by a chromosomal translocation?

A)deletion only
B)exchange of homologous chromosome fragments
C)nondisjunction
D)exchange of nonhomologous chromosome fragments

Question 35

Abnormal chromosomes are frequently found in cancerous malignant tumors.Errors such as translocations may place a gene in close proximity to different control regions of the DNA,which can make cells cancerous.Which of the following might then occur to make the cancer worse?

A)an increase in nondisjunction
B)expression of inappropriate gene products
C)a decrease in mitotic frequency
D)death of the cancer cells in the tumor

Question 36

Of the following human aneuploidies,which is the one that generally has the most severe impact on the health of the individual?

A)47,+21,Down syndrome
B)47,XXY,Klinefelter syndrome
C)47,XXX,Trisomy X
D)45,X0,Turner syndrome

Question 37

At what point in meiosis is a chromosome lost so that,after fertilization with a normal gamete,the result is an embryo with the chromosomal makeup of 45,X0?

A)after an error occurring in anaphase I or anaphase II
B)after an error occurring in anaphase I only
C)after an error occurring in anaphase II only
D)after an error occurring in prophase I only

Question 38

What is a syndrome?

A)a characteristic facial appearance
B)a group of traits,all of which must be present if an aneuploidy is to be diagnosed
C)a group of traits typically found in conjunction with a particular chromosomal alteration or gene mutation
D)a characteristic trait usually given the discoverer's name

Question 39

What is the source of the extra chromosome 21 in an individual with Down syndrome?

A)nondisjunction in the mother only
B)nondisjunction in the father only
C)duplication of the chromosome
D)nondisjunction in either parent

Question 40

A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves,due to an allele (a)of gene A;a feathered stem,due to an allele (b)of gene B;and hollow roots,due to an allele (c)of gene C.The three genes are linked and recombine.
A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and was able to identify progeny of the phenotypic distribution (+ = wild type)shown in the figure below.
Which of the following are the phenotypes of the parents in this cross?

A)2 and 5
B)1 and 6
C)4 and 8
D)3 and 7
E)1 and 2

Question 41

A man who is a dwarf due to achondroplasia and has 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.Achondroplasia 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?

A)0%
B)25%
C)50%
D)100%

Question 42

A man who is a dwarf due to achondroplasia and has 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.Achondroplasia is autosomal dominant,and red-green color blindness is X-linked recessive.
How many of the couple's daughters might be expected to be color-blind dwarfs?

A)all
B)none
C)half
D)one out of four

Question 43

A man who is a dwarf due to achondroplasia and has 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.Achondroplasia is autosomal dominant,and red-green color blindness is X-linked recessive.
What proportion of their sons would be color-blind and of normal height?

A)none
B)half
C)one out of four
D)three out of four