genetics ch.4
*Figure 4.9 Inheritance pattern of an X-linked trait in fruit flies* What ratio of offspring is expected from this cross of two Drosophila flies (Xw- Y x Xw+ Xw+)? a) 1 red-eyed male : 1 white-eyed female (All females will inherit the XW+ allele from their mothers along with the XW- allele from their fathers) b) 1 white-eyed male : 1 red-eyed female (Males inherit their X chromosome from their female parent who is homozygous for the red-eyed allele in this case) c) 1 white-eyed male : 1 white-eyed female d) 1 red-eyed male : 1 red-eyed female
1 red-eyed male : 1 red-eyed female
*Figure 4.9 Inheritance pattern of an X-linked trait in fruit flies* Consider this testcross between a white-eyed male fruit fly and a heterozygous red-eyed female. The offspring are expected in what proportion? a) 2 red-eyed males : 1 red-eyed female : 1 white-eyed female (The mother is heterozygous for the red-eyed allele. Half of her sons will inherit the allele for white eyes) b) 2 white-eyed males : 1 red-eyed female : 1 white-eyed female (The mother is heterozygous for the red-eyed allele. Half of her sons will inherit the allele for red eyes) c) 1 red-eyed male : 1 white-eyed male : 2 white-eyed females (Red-eyed females can be produced in this testcross) d) 1 red-eyed male : 1 white-eyed male : 1 red-eyed female : 1 white-eyed female e) 1 red-eyed male : 1 white-eyed male : 2 red-eyed females (White-eyed females can be produced in this testcross)
1 red-eyed male : 1 white-eyed male : 1 red-eyed female : 1 white-eyed female
Which of the following is an example of a testcross in Drosophila melanogaster? a) A cross between a white-eyed male and a white-eyed female b) A cross between a white-eyed male and a red-eyed female c) A cross between a red-eyed male and a white-eyed female ( the genotype of the male offspring is known in this case)
A cross between a white-eyed male and a red-eyed female
One form of hereditary deafness is inherited with an X-linked recessive allele. What can be expected for the offspring of a deaf mother and a father with normal hearing? a) All of the sons will be deaf and all of the daughters will have normal hearing. b) All of the children, sons, and daughters, will be deaf. c) None of the children will be deaf. (Sons will express the deafness allele inherited from their mother since the Y chromosome from their father does not have to carry any alleles to mask it.) d) All of the daughters will be deaf and all of the sons will have normal hearing
All of the sons will be deaf and all of the daughters will have normal hearing.
What is Barr body? a) An inactivated X chromosome in mammalian somatic cells b) An inactivated Y chromosome in mammalian somatic cells c) An inactivated autosome in mammalian somatic cells?
An inactivated X chromosome in mammalian somatic cells
What is the primary role of the X inactivation center (XIC)? a) compaction of the X Chromosome b) expression of female secondary characteristics c) upregulation of expression of genes on the X chromosome (X Inactivation relates to reduced gene activity)
Compaction of the X chromosome
In mammals, when does X inactivation occur? a) During gametogenesis b) Upon fertilization c) During adulthood, in all somatic cells d) During embryonic development
During embryonic development
True or false: All genes on the inactivated X chromosome remain inactivated throughout life in a somatic cell of an adult female a) True (Some genes on the inactivated X chromosome are expressed in the somatic cells of adult female mammals) b) False
False
True or false: Like X chromosomes in human females, one of the Z chromosomes in male birds is randomly inactivated in somatic cells. a) True (Studies suggest that some Z-liked genes may be dosage compensated, but many are not. b) False
False
Colorblindness is inherited with an X-linked recessive allele. Which term describes the genotype for a colorblind male? a) Homozygous dominant b) Hemizygous c) Homozygous recessive (Males only have one X chromosome, and cannot carry more than one allele for an X-linked trait. The correct term in this case is hemizygous) d) Heterozygous (Males only have one X chromosome, and cannot carry more than one allele for an X-linked trait. The correct term in this case is hemizygous
Hemizygous
Why is individual III-2 unaffected by Duchenne muscular dystrophy while her brother, individual III-3, inherited the disease? a) III-2 inherited an X chromosome from her mother that did not carry the disease allele. (DMD is an X linked recessive disorder. III-2 is a female and would have had to have inherited the recessive allele from both parents to express the trait. III-3 is a male and will only express the trait if inherited from his mother.) b) III-2 inherited an X chromosome from her father that did not carry the disease allele. c) III-3 inherited two copies of the allele for the disease. d) III-3 inherited the disease allele from his father rather than his mother.
III-2 inherited an X chromosome from her father that did not carry the disease allele.
In his experiment, Morgan crossed a red-eyed female with a white-eyed male. Which of the following results allowed Morgan to conclude that the locus affecting eye color was on the X chromosome? a) In the F2 generation, half of males and females had red eyes, while the other half had white eyes. (This pattern would show autosomal inheritance rather than X linkage) b) In the F2 generation, all females had red eyes, while half of the males had red eyes and the other half had white eyes. c) In the F1 generation, all male and female flies had white eyes. d) In the F2 generation, all males had red eyes, while half of the females had red eyes and the other half had white eyes. (F2 males inherit an X chromosome from the F1 female, who is heterozygous for the eye color trait. e) In the F1 generation, all male and female flies had red eyes.
In the F2 generation, all females had red eyes, while half of the males had red eyes and the other half had white eyes.
During which phase of X chromosome inactivation is one of the X chromosomes chosen to be inactivated? a) Spreading (The X chromosome is targeted for inactivation during the initiation phase. The actual inactivation occurs during the spreading phase) b) Initiation c) Maintenance
Initiation
*Figure 4.6 The Mechanism of X Chromosome Inactivation a) cells* An alternate name for the mechanism of X chromosome inactivation (shown in the figure) is the ___ hypothesis
Lyon
*Figure 4.6 The Mechanism of X Chromosome Inactivation* The image is depicting the mechanism of X chromosome inactivation, called the a) maternal effect b) theory of independent assortment c) genomic imprinting d) Lyon hypothesis
Lyon hypothesis
How is dosage compensation for X-linked genes achieved in the fruit fly, Drosophila melanogaster? a) Males increase the expression of genes on the X chromosome b) Females randomly inactivate one of the X chromosomes ( X chromosome inactivation occurs in female mammals) c) Females reduce the expression of genes on the X chromosome d) The X and the Y chromosome contain the same genes, so dosage compensation is unnecessary
Males increase the expression of genes on the X chromosome
Which species achieves dosage compensation by inactivating the paternally derived X chromosome in all somatic cells of a female? a) Humans (In humans, either the maternal or paternal X chromosome is randomly inactivated in somatic cells of females) b) Caenorhabditis elegans ( IN Caenorhabditis elegans, the level of expression on both X chromosomes in hermaphrodites is decreased to 50% levels compared with males) c) Drosophila melanogaster (In Drosophila melanogaster, the level of expression of genes on the X chromosome in males is increased twofold) d) Marsupial mammals
Marsupial mammals
A female with Turner syndrome (XO) would have how many Barr bodies in her cells? a) none b) three c) one d) two
None
A male with Klinefelter syndrome (XXY) would have how many Barr bodies in his cells? a) One b) None c) Two (The number of Barr bodies is equal to the number of X chromosomes minus one) d) Three
One
The Xist gene on the X chromosome encodes a(n) a) RNA molecule that coats the X chromosome and inactivates it b) transcription factor that activates female-specific genes c) transcription factor that represses transcription of genes on the Y chromosome d) RNA molecule that activates expression of genes on the X chromosome
RNA molecule that coats the X chromosome and inactivates it
When Thomas Hunt Morgan crossed the red-eyed F1 generation fruit flies with each other, the F2 generation included both red-eyed and white-eyed individuals. Interestingly, all the white-eyed flies were male. What did these results indicate? a) Eye color in fruit flies is influenced by male-specific non-chromosome factors b) Eye color in fruit flies is influenced by female-specific non-chromosome factors c) The eye color gene was on the Y chromosome ( the data suggested that eye color alleles are located on the X chromosome) d) The eye color gene was on the X chromosome e) The eye color gene was on an autosome
The eye color gene was on the X chromosome
What scientist first confirmed the location of a gene on a particular chromosome when he demonstrated that a gene affecting eye color in fruit flies is on the X chromosome? a) Archibald Garrod b) Thomas Hunt Morgan c) James Watson d) Gregor Mendel
Thomas Hunt Morgan
The short region on the X chromosome that plays an important role in X chromosome inactivation is the _____
XIC
Which gene of the XIC encodes an RNA that will coat an X chromosome leading to its inactivation? a) Turner syndrome gene b) Xist gene c) SRY gene d) Dystrophin gene
Xist gene
In birds males are ZZ and females are ZW. studies have shown that male birds express twice as much gene product of some Z-linked genes. What does this suggest? a) one of the Z chromosomes is randomly inactivated in birds (The level of Z-linked gene expression should be equal if inactivation occurred) b) Z-linked genes are not dosage compensated in birds c) Female birds decrease Z gene expression by 50%
Z-linked genes are not dosage compensated in birds
Match the phases of X chromosome inactivation with the correct description a) Initiation b) Spreading c) Maintenance A) Occurs from embryonic development throughout life to preserve the state of X chromosome inactivation B) Xist gene encodes an RNA that coats the X chromosome leading to recruitment of proteins that promote compaction C) X chromosome is targeted for inactivation
a) Initiation->X chromosome is targeted for inactivation b) Spreading-> Xist gene encodes an RNA that coats the X chromosome leading to recruitment of proteins that promote compaction c) Maintenance -> Occurs from embryonic development throughout life to preserve the state of X chromosome inactivation
A mammal is heterozygous for two alleles of a gene on the X chromosome. These alleles are designated B and b. If, during embryonic development, a cell inactivates the X chromosome that carries B, then when that cell divides, the B allele will be inactivated in a) some of its descendants, but the proportion cannot be predicated b) all of its descendants c) half of its descendants
all of its descendants
*Figure 4.5 X Chromosome Inactivation in Female Mammals a) Red Cell* The inactivated X chromosome in somatic cells of mammals, like the one on the right side of this image, is called a ___ ___
barr body
Which genes on the X chromosome are able to escape the effects of X chromosome inactivation in female mammalian cells? a) FoxP3 b) SRY gene c) Xist gene d) Pseudoautosomal genes
c) Xist gene d) Pseudoautosomal gene
Select all of these that are phases of X chromosome inactivation a) elongation b) termination c) initiation d) maintenance e) spreading
c) initiation d) maintenance e) spreading
The underlying mechanism by which an individual develops into a male or a female is called sex ____
determination
Despite the fact that human males are XY and human females are XX, they have equal expression of many genes on their sex chromosomes. This phenomenon called ___ ____
dosage compensation
What accounts for equal expression of genes on the sex chromosome despite the fact that males and females have an unequal complement of sex chromosomes? a) dosage compensation b) sex influenced inheritance c) sex limited inheritance d) maternal effect
dosage compensation
To equalize gene expression of genes on the X chromosome, in Drosophila melanogaster, males ____ the expression of genes on the X chromosome.
double
Which species achieves dosage compensation by increasing the expression of genes on the X-chromosome in males by twofold? a) humans (In humans, either the maternal or paternal X chromosome is randomly inactivated in somatic cells of females. b) marsupial mammals (Marsupial mammals achieve dosage compensation by inactivating the paternally derived X-chromosome in all somatic cells of a female) c) Caenorhabditis elegans (In Caenorhabditis elegans, the level of expression on both X chromosomes in hermaphrodites is decreased to 50% levels compared with males) d) drosophila melanogaster
drosophila melanogaster
Muscle cells in people with Duchenne muscular dystrophy show weakening of the cytoskeleton due to a deficiency of the protein ____
dystrophin
Muscular weakness in Duchenne muscular dystrophy is caused by a deficiency of ______ that normally connects the ______ to the ______. a) dystrophin; cell nucleus; cytoskeleton b) dystrophin; cytoskeleton; plasma membrane c) myosin; cytoskeleton; cell nucleus d) actin; cytoskeleton; mitochondrion
dystrophin; cytoskeleton; plasma membrane
For mammals, X inactivation occurs during the development of a(n) a) embryo b) ovary or testis c) adult tissue d) gamete (X inactivation in a gamete could prevent the expression of X chromosome genes in early development)
embryo
Thomas Hunt Morgan carried out the first study in which the location of a gene was assigned to a particular chromosome in a fruit fly. This gene affected ____, and it was located on the chromosome a) eye color; X b) sex determination; X c) eye color; Y d) sex determination; Y
eye color; X
X-linked alleles are never transmitted from a) father to son. b) mother to daughter. c) mother to son. d) father to daughter.
father to son
In humans with a typical constitution of chromosomes, X-chromosomes inactivation induces dosage compensation by randomly inactivating one of the X-chromosomes in the somatic cells of a) females b) both males and females c) males
females
Hemophilia is an X-linked recessive trait. In order for a female child to have hemophilia a) her mother must have hemophilia but her father must not have the disease. b) her mother must have hemophilia. c) her father and mother must have hemophilia. d) her father must have hemophilia and her mother may have hemophilia or be a carrier.
her father must have hemophilia and her mother may have hemophilia or be a carrier.
Hemophilia is an X-linked recessive trait. In order for a female child to have hemophilia a) her mother must have hemophilia. b) her father and mother must have hemophilia. c) her mother must have hemophilia but her father must not have the disease. d) her father must have hemophilia and her mother may have hemophilia or be a carrier.
her father must have hemophilia and her mother may have hemophilia or be a carrier.
In C. elegans, the expression of genes on the X chromosome is diminished to 50% in a) females b) hermaphrodites x)males
hermaphrodites
One form of hereditary deafness is inherited with an X-linked recessive allele. A woman with normal hearing has a son with hereditary deafness. The woman's genotype at this gene locus is a) hemizygous. b) heterozygous. c) homozygous.
heterozygous
*Figure 4.10 A human pedigree for Duchenne muscular dystrophy, an X-linked recessive trait* This is a pedigree for Duchenne muscular dystrophy, an X-linked recessive trait. Individual IV-6 inherited the mutation that causes Duchenne muscular dystrophy from a) both his mother and his b) father. c) his father. d) his mother. e) either his mother or his father.
his mother
What are the three phases of X chromosomes inactivation? a) replication, transcription and translation b) initiation, elongation and termination c) initiation, spreading and maintenance d) denaturation, annealing and elongation
initiation, spreading and maintenance
After an embryonic cell inactivates an X chromosome, when the cell divides, its descendants will ___ a) randomly inactivate one of the two X chromosomes after each cell division (Since inactivation has already occurred, the process can no longer be random) b) maintain inactivation of the same X chromosome c) always inherit only the X chromosome that remains active d) always inherit only the X chromosome that was inactivated
maintain inactivation of the same X chromosome
A cross in which the sexes and phenotypes are reversed compared to a previous cross is called a(n) ____ cross.
reciprocal
For X-linked genes, ______ crosses give different outcomes. a) one-sided b) similar c) reciprocal d) multiple (the same cross performed multiple times will give the same outcome)
reciprocal
In C. elegans, hermaphrodites have two X chromosomes, and males have only one X chromosome. Dosage compensation is accomplished by a) increasing the expression of genes on the X chromosomes in males (Dosage compensation occurs in the XX hermaphrodite) b) destroying one of the X chromosomes in hermaphrodites c) randomly inactivating one of the X chromosomes in hermaphrodites (X chromosome inactivation occurs in female mammals) d) reducing the expression of genes on the X chromosome in hermaphrodites
reducing the expression of genes on the X chromosome in hermaphrodites
In a Drosophila melanogaster _____, a fly with a dominant phenotype and unknown genotype is mated to one that has a recessive phenotype.
testcross
*Figure 4.5 X Chromosome Inactivation in Female Mammals a) Cat* The coat color of the calico cat shown in the image is best explained by ____ a) maternal effect b) The Lyon hypothesis c) paternal effect d) codominance (X chromosome inactivation is a random process that occurs early on in development. This is what accounts for the variegated phenotype)
the Lyon hypothesis
*Figure 4.6 The Mechanism of X Chromosome Inactivation b) Mice* As shown in the image, X chromosomes are randomly inactivated during embryonic development. This is also called ____ a) the Lyon hypothesis b) codominance c) paternal effect d) maternal effect
the Lyon hypothesis
A trait that a son can inherit only from his mother must be due to an allele found on a) the X chromosome b) the Y chromosome c) an autosome
the X chromosome
When a daughter can inherit a sex-linked allele from either her mother or father, it must be located on a) the Y chromosome b) an autosome c) the X chromosome
the X chromosome
X-linked traits do not show the same outcomes in reciprocal crosses because a) the mother contributes an X chromosome only to her sons. (A mother passes an X chromosome to both her sons and daughters.) b) the father contributes an X chromosome only to his daughters. c) the mother contributes an X chromosome only to her daughters.
the father contributes an X chromosome only to his daughters.
What is sex determination? a) the mechanism by which an individual develops into a female or a male b) the process in which male and female gametes are formed c) a laboratory technique in which the sex chromosome karyotype of an individual is determined
the mechanism by which an individual develops into a female or a male
Colorblindness is due to an X-linked recessive allele. To be colorblind, females must inherit ______ copy(ies) of this allele and males must inherit ______ copy(ies). a) one; one b) one; two c) two; two d) two; one
two; one
In somatic cells of human females one of the two X chromosomes is randomly turned off. What is this mechanism called? a) paternal leakage b) x-chromosome inactivation c) maternal effect d) endosymbiosis
x-chromosome inactivation
