Biology: The Unity and Diversity of Life (MindTap Course List)
14th Edition
ISBN: 9781305073951
Author: Cecie Starr, Ralph Taggart, Christine Evers, Lisa Starr
Publisher: Cengage Learning
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Chapter 10, Problem 3CT
Almost all calico cats (one is pictured in FIGURE 10.7B) are female. Why?
B When this calico cat was an embryo, one of the two X chromosomes was inactivated in each of her cells. The descendants of the cells formed her adult body, which is a mosaic for expression of X chromosome genes. Black fur arises in patches where genes on the X chromosome inherited from one parent are expressed; orange fur arises in patches where genes on the X chromosome inherited from the other parent are expressed.
FIGURE 10.7 ►Animated X chromosome inactivation.
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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?
Figure 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.
Cat fur coat color genetics is interesting. Orange fur is dominant (''B'') to black fur (''b'') and piebald, which is white spotting, is dominant (''S'') to non-white-spotted (''s''). Both of those genes are located on the X chromosome. In addition, in cats, somatic cells exhibit X-inactivation randomly, which explains why there are tortoiseshell cats (when heterozygous, have orange and black spots) as well as calico cats (orange and black but also with white spots). An orange and white spotted male is mated with a tortoiseshell female.
Draw a dihybrid Punnet square to show the possible offspring:
Chapter 10 Solutions
Biology: The Unity and Diversity of Life (MindTap Course List)
Ch. 10 - The expression of a gene may depend on _______. a....Ch. 10 - Prob. 2SQCh. 10 - Binding of ______ to _______ in DNA can increase...Ch. 10 - Prob. 4SQCh. 10 - Prob. 5SQCh. 10 - Muscle cells differ from bone cells because...Ch. 10 - Prob. 7SQCh. 10 - Homeotic gene products _______. a. flank a...Ch. 10 - A gene that is knocked out is ________. a. deleted...Ch. 10 - Which of the following includes all of the others?...
Ch. 10 - Prob. 11SQCh. 10 - Effect of Paternal Grandmothers Food Supply on...Ch. 10 - Prob. 2DAACh. 10 - Effect of Paternal Grandmothers Food Supply on...Ch. 10 - Prob. 12SQCh. 10 - A cell with a Barr body is ___ . a. a bacterium b....Ch. 10 - Operons _____. a. only occur in bacteria b. have...Ch. 10 - Prob. 15SQCh. 10 - Why are some genes expressed and some not?Ch. 10 - Prob. 2CTCh. 10 - Almost all calico cats (one is pictured in FIGURE...Ch. 10 - The photos above show flowers from Arabidopsis...
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- Following X-chromosome inactivation, most of the genes on theinactivated X chromosome are silenced. Explain how. Name onegene that is not silenced.arrow_forwardHuman 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.)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
- Hi! I would love to get some help on the box-and arrow model question! :) A male individual who is XYSRY has the following genotype for the AMH gene on chromosome 19: AMH1 AMH2. The AMH1 allele codes for a protein that is capable of binding to the receptor for AMH. The AMH2 allele codes for a protein that is unable to bind with the receptor for AMH. Based on your understanding of biology, what is the likely phenotype of this individual? Humans have 23 pairs of chromosomes of which 22 pairs are autosomal and the 23rd pair is sex-linked.In a human female, the sex chromosome pair is represented as XX, whereas, in a human male, it is represented as XY.AMH is an anti-Mullerin hormone produced by the Sertoli cells in males and helps in the development of the sex organs. Each pair of chromosomes has a pair of genes called alleles at the same loci representing a single character. Each gene of an allele represents the expression of the character.A gene can either show expression or…arrow_forwardOne of the X chromosomes in a particular Drosophila female had a normal order of genes but carried recessive alleles of the genes for yellow body color (y), vermilion eye color (v), and forked bristles (f), as well as the dominant X-linked Bar eye mutation (B). Her other X chromosome carried the wild-type alleles of all four genes, but the region including y, v, and f (but not B) was inverted with respect to the normal order of genes. This female was crossed to a wild-type male as diagrammed here. 1. Draw the meiotic prophase I chromosomes with maximal pairing from the inversion heterozygous female. 2. (continued) When a crossover occurs between v and f, please draw the resulting chromosomes in four gametes.arrow_forwardWhich of the following statements about calico cats is true? Select all that apply. Black fur sections are found in regions that are formed from cells that inactivated the X chromosome with the orange allele of the fur color gene. a. Black and orange sections of fur on calico cats will always be the same size, since X chromosome inactivation always happens at the same stage of development. b. Black fur sections are found in regions that are formed from cells that inactivated the paternal X chromosome. C. Black sections of fur in calico cats will always be located on the same body locations. d. Calico cats are only females, except in cases of chromosomal number abnormalities. D e.arrow_forward
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