Study Guide for Campbell Biology
11th Edition
ISBN: 9780134443775
Author: Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Jane B. Reece, Martha R. Taylor, Michael A. Pollock
Publisher: PEARSON
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Textbook Question
Chapter 15, Problem 17TYK
Some girls who fail to undergo puberty are found to have Swyer syndrome, a condition in which they are externally female but have an XY genotype. Which of the following statements may explain the origin of this syndrome?
- a. A mutation in the XIST gene, which codes for RNA molecules that coat the X chromosome and initiate X-inactivation, must have occurred.
- b. A nondisjunction in the egg from the mother resulted in both sex chromosomes coming from the father. Genomic imprinting of the father’s X chromosome then caused the development of a female
phenotype . - c. These individuals are actually XXY; the second X is not seen because it is condensed into a Barr body. They have small testes and are sterile but otherwise appear female.
- d. A mutation or deletion of the SRY gene on the Y chromosome prevented development of testes and production of the male sex hormones required for a male phenotype.
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Chapter 15 Solutions
Study Guide for Campbell Biology
Ch. 15 - Complete the following summary of Morgans crosses...Ch. 15 - Two normal color-sighted individuals have two...Ch. 15 - In a testcross between a heterozygote tall,...Ch. 15 - With unlinked genes, an equal number of parental...Ch. 15 - The following recombination frequencies have been...Ch. 15 - a. What is the difference between an organism with...Ch. 15 - Prob. 7IQCh. 15 - Prob. 8IQCh. 15 - Mendels law of independent assortment applies to...Ch. 15 - You have found a new mutant phenotype in fruit...
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- Which of the following statements regarding X-inactivation is TRUE?(posted) Inactivated X chromosomes are only found in somatic cells of females. After X-inactivation happens in a cell, all daughter cells resulting from mitotic events of that cell will have the same X chromosome ina none of the statements listed here are true X-inactivation is a random event that happens during human development right before a fetus is born. all of the statements listed here are true)arrow_forwardFollowing X-chromosome inactivation, most of the genes on theinactivated X chromosome are silenced. Explain how. Name onegene that is not silenced.arrow_forward4) Explain why you can NOT typically have a Male Calico cat. 5) Can you think of any unusual situation where you might be able to have a Male Calico cat? Explain how this might occur 6) Explain 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_forward
- Occasionally, a mouse X chromosome is broken into two pieces and each piece becomes attached to a different autosome. A scientist studies this cell, and finds that the genes on only one of the two pieces undergo inactivation. By referring to the mechanism of X-chromosome inactivation, explain the observation made by the scientist.arrow_forwardFigure 19.25 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 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 35, 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.arrow_forwardIn Drosophila, the X chromosomes may become attached to one another (XXn ) such that they always segregate together. Some flies thus contain a set of attached X chromosomes plus a Y chromosome. (a) What sex would such a fly be? Explain why this is so. (b) Given the answer to part (a), predict the sex of the off-spring that would occur in a cross between this fly and a normal one of the opposite sex. (c) If the offspring described in part (b) are allowed to interbreed, what will be the outcome?arrow_forward
- Colorblindness and hemophilia are both X-linked traits in humans. Explain how a female who has a defective color vision gene on one X chromosome and a defective blood clotting gene causing hemophilia on the other X chromosome can be neither a hemophiliac nor colorblind? Please discuss the effect of Gene dosage compensation in your answer and in your answer describe the molecular process by which this occurs.arrow_forwardImagine 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"arrow_forwardYou are interested in the expression of regions of the X chromosome at different times in human fetal development. You hypothesize that large regions of the X chromosomes will be expressed at times when parts of the reproductive organs are developing. What structural and chemical characteristics of the X chromosome might you look at over time to determine when expression of genes on the X chromosome is enhanced or repressed?arrow_forward
- Theodor Boveri predicted that malignancies would often be associated with chromosomal mutation. What lines of evidence substantiate this prediction?arrow_forwardIn the past, the IOC has employed two genetic sex- determination tests. The Barr body test screens for the presence of two X chromosomes. In XX somatic cells, one copy of the X chromosome condenses into a largely inactive structure called a Barr body, which can be seen using a light microscope. In more recent years, a polymerase chain reaction-based screen has been used to amplify the DNA sequence of the SRY gene, which is found only on the Y chromosome. Based on their karyotypes, what would be the outcome of these two tests for each of the four individuals? Drag the labels to indicate the presence or absence of a Barr body and the SRY gene sequence.arrow_forwardDescribe when X-chromosome inactivation occurs and how thisleads to phenotypic results at the organism level. In your answer,you should explain why XCI causes results such as variegated coatpatterns in mammals. Why do two different calico cats have theirpatches of orange and black fur in different places? Explainwhether or not a variegated coat pattern due to XCI could occur inmarsupials.arrow_forward
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