Genetics: From Genes to Genomes
6th Edition
ISBN: 9781259700903
Author: Leland Hartwell Dr., Michael L. Goldberg Professor Dr., Janice Fischer, Leroy Hood Dr.
Publisher: McGraw-Hill Education
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Chapter 17, Problem 42P
Figure 17.29 shows that the Sxl protein binds to the mRNA of the msl-2 gene, inhibiting translation of the mRNA’s proper reading frame. The MSL-2 protein is a transcription factor that binds to the X chromosome in 42.XY males to double the level of X-linked gene transcription, thus equalizing X-linked gene expression in XY males and XX females.
| a. | In which sex, XY males or XX females, would the Sxl protein bind to the msl-2 mRNA? |
| b. | As discussed in Problem 41, some Sxl alleles are lethal to females and others are lethal to males. Is the function of Sxl in regulating the synthesis of Msl-2 protein sufficient to explain the sex-specific lethality caused by both kinds of alleles? |
| c. | Predict the effect of loss-of-function mutations in msl-2 on male and female fertility and viability. |
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In humans, dosage compensation is accomplished by:
inactivating one X chromosome in female somatic cells
inactivating one homolog from each homologous pair of chromosomes in female somatic cells
inactivating the Y chromosome in male somatic cells
increasing gene expression from the X chromosome in male somatic cell
Human females who are heterozygous for an X-linked recessive allele sometimes exhibit mild expression of the trait. However, such mild expression of X-linked traits in females who are heterozygous for Xlinked alleles is not seen in Drosophila. What might cause this difference in the expression of X-linked genes between human females and female Drosophila? (Hint: In Drosophila, dosage compensation is accomplished by doubling the activity of genes on the X chromosome of males.)
Imagine a scenario in which prenatal testing of a human female fetus indicates that the baby will have a normal XX karyotype but is heterozygous for a mutation that inactivates the Xist promoter. Allele “Xr” represents the mutated version of the Xist promoter, and “XR” represents the normal version of the Xist promoter.
How will this mutation affect the process of X inactivation?A. "X inactivation will still be random with both mutant and normal X chromosomes being randomly inactivated"
B. "The chromosome with the mutant Xist promoter will always be active"
C. "The chromosome with the mutant Xist promoter will always be inactivated"
D. "The normal X chromosome (no mutation in Xist) will always be active"
E. "The normal X chromosome (no mutation in Xist) will always be inactivated"
Chapter 17 Solutions
Genetics: From Genes to Genomes
Ch. 17 - For each of the terms in the left column, choose...Ch. 17 - For each of the following types of gene...Ch. 17 - List five events other than transcription...Ch. 17 - Which eukaryotic RNA polymerase RNA pol I, pol II,...Ch. 17 - As shown in the following diagram, a single...Ch. 17 - You have synthesized an enhancerless GFP reporter...Ch. 17 - Prob. 7PCh. 17 - Prob. 8PCh. 17 - A single UAS regulates the expression of three...Ch. 17 - MyoD is a transcriptional activator that turns on...
Ch. 17 - a. Assume that two transcription factors are...Ch. 17 - Prob. 12PCh. 17 - In Problem 12, you identified a genomic region...Ch. 17 - Prob. 14PCh. 17 - Prob. 15PCh. 17 - Genes in both prokaryotes and eukaryotes are...Ch. 17 - Prob. 17PCh. 17 - Lysine 4 of histone H3 H3K4 is methylated in the...Ch. 17 - J.T. Lis and collaborators have developed an...Ch. 17 - Hydatiform moles are growths of undifferentiated...Ch. 17 - Prader-Willi syndrome is caused by a mutation in...Ch. 17 - The human IGF2 gene is autosomal and maternally...Ch. 17 - Follow the expression of a paternally imprinted...Ch. 17 - Reciprocal crosses were performed using two inbred...Ch. 17 - Interestingly, imprinting can be tissue-specific....Ch. 17 - Prob. 26PCh. 17 - A method for detecting methylated CpGs involves...Ch. 17 - Honeybees Apis mellifera provide a striking...Ch. 17 - Consider the experiment in Fig. 17.24, where the...Ch. 17 - A protein or RNA that regulates gene expression in...Ch. 17 - a. How can a single eukaryotic gene give rise to...Ch. 17 - A hunchback gene, a gene necessary for proper...Ch. 17 - You know that the mRNA and protein produced by a...Ch. 17 - You are studying a transgenic mouse strain that...Ch. 17 - Prob. 35PCh. 17 - Scientists have exploited the siRNA pathway to...Ch. 17 - Persimmons Diospyros lotus are dioecious plants,...Ch. 17 - Drosophila females homozygous for loss-of-function...Ch. 17 - The text has discussed the RNA-Seq technique,...Ch. 17 - Researchers know that Fru-M controls male sexual...Ch. 17 - The Drosophila gene Sex lethal Sxl is deserving of...Ch. 17 - Figure 17.29 shows that the Sxl protein binds to...
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- Which of the following applies to the female sex determination in Drosophila melanogaster fruit flies? (Mark all that apply) When the X:A ratio is 1.0, the SXL gene is transcribed during the early embryonic stages. The SXL protein inhibits the expression of female differentiaion genes The SXL protein promotes the correct splicing of the Tra pre-mRNA so that functional Tra protein is made. The presence of the SXL protein promotes the correct splicing of the SXL pre-mRNA during later embryonic stages to ensure to continuous production of SXL protein. The Tra protein will stimulate the expression of male-specific genes.arrow_forwardDescribe the molecular process of X-chromosome inactivation.This description should include the three phases of inactivationand the role of the Xic. Explain what happens to the X chromosomes during embryogenesis, in adult somatic cells, and duringoogenesis.arrow_forwardDuchenne Muscular Dystrophy (DMD) is a disorder that primarily affects the function of skeletal muscles used for movement and cardiac muscles used for heart beating. Dystrophin is a protein encoded by a single gene, DMD, that is expressed in skeletal and cardiac muscle. Some forms of muscular dystrophy may be caused by different mutations in the DNA sequence of the DMD gene. Because the DMD locus is on the X chromosome, males are affected at higher rates. Two brothers, one of whom has DMD and one of whom does not, worked with their genetic counselor (Links to an external site.) to have their DMD gene sequenced to identify genetic variation that may explain why one brother was affected and the other not. Because DMD is a very long gene, a fictionalized, simplified model of the results is presented here (Figure 1). The actual DMD mRNA is about 16,000 base-pairs!------Consider single nucleotide polymorphism (SNP) #1 (Figure 1). Is this mutation likely to cause Duchenne muscular…arrow_forward
- XX individuals can be sex-reversed males if one of their X chromosomes contains a translocated portion of the Y chromosome that includes the SRY gene. In light of what you now know about X-chromosome inactivation, it seems that this karyotype might have more complex consequences. In fact, although most such males are completely sex-reversed, X-chromosome inactivation can cause some of these XX males to have varying degrees of residual female characteristics. a. X-chromosome inactivation in normal XX embryos occurs earlier in development than SRY production in normal XY embryos. When present on a translocation X chromosome, SRY is subject to inactivation. Formulate a hypothesis to explain why many XX individuals with a translocation X chromosome that includes the SRY gene are not completely sex-reversed (male). b. Based on your answer to part (a), why do you think some individuals with this karyotype are completely sex-reversed?arrow_forwardIn Drosophila sex determination (Check all that apply.) A) XY individuals transcribe the Sxl gene early but not late. B XX individuals carry the Sxl gene, XY individuals do not. XX individuals transcribe the Sxl gene, XY individuals do not. XX individuals express the Sxl protein, XY individuals do not. E) The Sxl transcript (Pre-MRNA) is spliced differently in XX compared to XY individuals.arrow_forwardA mutation occurs in the Drosophila doublesex gene that prevents Tra from binding to the dsx RNA transcript. What would be the consequences of this mutation for Dsx protein expression in males? In females?arrow_forward
- Explain about how X chromosome inactivation takes place in mammals at the chromosomal and molecular level. B. What genes are involved in inactivating a human X chromosome? . C. What role does X chromosome-specific inactivating transcript --XIST-- non coding RNA play in the inactivation of the human X chromosome.arrow_forwardWhen the organization of adjacent genes with highly similar sequences is in an inverted orientation, this can reduce the expression of other genes that have similar sequence and are located on other chromosomes. Explain the mechanism of how this generally occurs.arrow_forwardDefine the Random Monoallelic Expression: Inactivation of the X Chromosome ?arrow_forward
- Following X-chromosome inactivation, most of the genes on theinactivated X chromosome are silenced. Explain how. Name onegene that is not silenced.arrow_forwardLid (Little imaginal discs) is a gene located on chromosome 2L and FRT40A refers to an FRT sequence inserted at the 40A (cytological location). Tubulin (Tub) refers to a promoter that can drive target gene expression in all the cell types. Gal80 is an inhibitor of Gal4 that blocks Gal4’s ability to activate transcription. Determine whether the following statements are true or false for flies with the following genotype: y w HsFLP; lid, FRT40A / P{Tub-Gal80}, FRT40A; P{Tub-Gal4} P{UAS-GFP} / + A. The fly will express Gal4, which will activate GFP in all the somatic cells without heat shock. B. After heat shock, FLP recombinase will be induced, which will induce mitotic recombination at FRT40A. However, lid mutant clone will be not induced because it is located closer to the centromere than FRT40A. C. After heat shock, FLP recombinase will be induced, which will induce mitotic recombination at FRT40A, resulting in the generation of homozygous lid mutant clones and twin spots that are…arrow_forwardUse the dropdowns to indicate the pattern of methylation and gene expression expected for a maternally-imprinted gene in the somatic cell of a male individual. The Somatic cell would show [Select] male's male parent, and [Select] male's female parent. As a result, [Select] of the allele inherited from the of the allele inherited from the could be expressed. The pattern of methylation would be [Select] imprinted gene in a somatic cell of a female individual. for the same maternally-arrow_forward
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