Genetics: Analysis and Principles
6th Edition
ISBN: 9781259616020
Author: Robert J. Brooker Professor Dr.
Publisher: McGraw-Hill Education
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Chapter 5, Problem 13CONQ
Describe when X-chromosome inactivation occurs and how this leads to
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Although most tortoiseshell cats are female, a litter of kittens will occasionally contain a male tortoiseshell. Which of the following can explain tortoiseshell coat color in a male kitten? Please explain in detail.
The male kitten has an extra Y chromosome
The male kitten has an extra X chromosome
The male kitten has no X chromosome
The male kitten cannot carry out X-inactivation
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?
One 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.
Chapter 5 Solutions
Genetics: Analysis and Principles
Ch. 5.1 - A female snail that coils to the left has...Ch. 5.1 - 2. What is the molecular explanation for maternal...Ch. 5.2 - 1. In fruit flies, dosage compensation is achieved...Ch. 5.2 - 2. According to the Lyon hypothesis,
a. one of...Ch. 5.2 - Prob. 3COMQCh. 5.3 - 1. In mice, the copy of the Igf2 gene that is...Ch. 5.3 - 2. A female mouse that is is crossed to a male...Ch. 5.3 - Prob. 3COMQCh. 5.3 - Prob. 4COMQCh. 5.4 - 1. Extranuclear inheritance occurs due to
a....
Ch. 5.4 - 2. A cross is made between a green four-o’clock...Ch. 5.4 - 3. Some human diseases are caused by mutations in...Ch. 5.4 - 4. Chloroplasts and mitochondria evolved from an...Ch. 5 - Define the term epigenetic inheritance, and...Ch. 5 - 2. Describe the inheritance pattern of maternal...Ch. 5 - A maternal effect gene exists in a dominant N...Ch. 5 - 4. A Drosophila embryo dies during early...Ch. 5 - 5. For Mendelian inheritance, the nuclear genotype...Ch. 5 - Suppose a maternal effect gene exists as a...Ch. 5 - Suppose that a gene affects the anterior...Ch. 5 - Explain why maternal effect genes exert their...Ch. 5 - As described in Chapter 22, researchers have been...Ch. 5 - 10. With regard to the numbers of sex chromosomes,...Ch. 5 - 11. What is a Barr body? How is its structure...Ch. 5 - Among different species, describe three distinct...Ch. 5 - 13. Describe when X-chromosome inactivation occurs...Ch. 5 - 14. Describe the molecular process of X-chromosome...Ch. 5 - Prob. 15CONQCh. 5 - 16. How many Barr bodies would you expect to find...Ch. 5 - 17. Certain forms of human color blindness are...Ch. 5 - A black female cat (XBXB) and an orange male cat...Ch. 5 - Prob. 19CONQCh. 5 - When does the erasure and reestablishment phase of...Ch. 5 - In what types of cells would you expect de novo...Ch. 5 - 22. On rare occasions, people are born with a...Ch. 5 - Genes that cause Prader-Willi syndrome and...Ch. 5 - Prob. 24CONQCh. 5 - What is extranuclear inheritance? Describe three...Ch. 5 - Prob. 26CONQCh. 5 - Among different species, does extranuclear...Ch. 5 - Extranuclear inheritance often correlates with...Ch. 5 - Prob. 29CONQCh. 5 - Prob. 30CONQCh. 5 - Which of the following traits or diseases is (are)...Ch. 5 - Prob. 32CONQCh. 5 - 33. Describe how a biparental pattern of...Ch. 5 - Figure 5.1 describes an example of a maternal...Ch. 5 - 2. Discuss the types of experimental observations...Ch. 5 - Prob. 3EQCh. 5 - As a hypothetical example, a trait in mice results...Ch. 5 - You have a female snail that coils to the right,...Ch. 5 - Prob. 6EQCh. 5 - 7. Figure 5.6 describes the results of...Ch. 5 - Prob. 8EQCh. 5 - In the experiment of Figure 5.6, why does a clone...Ch. 5 - Prob. 10EQCh. 5 - 11. A variegated trait in plants is analyzed using...Ch. 5 - 1. Recessive maternal effect genes are identified...Ch. 5 - Prob. 2QSDC
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- 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.arrow_forwardThe dosage of X chromosome expression is equalized between male and female mammals. Think about the example of calico cats to answer the following questions. Use Xb to represent the allele for black fur, XB to represent the allele for orange fur. What genotype(s) of female cats is/are expected to have a calico coat? Is it possible to have a calico cat that is male? Explain.arrow_forwardBarr bodies are formed to adjust X chromosome dosage in species other than humans, such as Drosophila (fruit flies) and C. elegans (nematodes). True or False ?arrow_forward
- 4) 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_forwardMales of many diploid species (like us) have X and Y sex chromosomes. They are hemizygous for most X- linked genes. Thus, males express most X-linked alleles, whether they are dominant or recessive in females. In the fruit fly Drosophila, it is common to achieve the equivalent of a test cross of X-linked genes in females by assessing the readily observed phenotypes of their male progeny. Since males do not receive X-linked genes from their father, sires of these crosses can be normal or wild-type flies. In fly genetics, it is conventional to name a gene after the mutant phenotype that enabled its discovery. Your challenge is to establish gene order and map distances between three X-linked genes in Drosophila. Each gene is represented by recessive mutant alleles that express rather distinctive phenotypes relative to their dominant wild-type alternative alleles. Flies expressing fruitless (f) are bisexual, lush (1) have a heightened responses to ethanol, and ken&barbie (kb) lack external…arrow_forwardThe mutations called bobbed in Drosophila result from variable reductions (deletions) in the number of amplified genes coding for rRNA. Researchers trying to maintain bobbed stocks have often documented their tendency to revert to wild type in successive generations. Propose a mechanism based on meiotic recombination which could account for this reversion phenomenon. Why would wild-type flies become more prevalent in Drosophila cultures?arrow_forward
- The beach mouse (Peromyscus polionotus) is a small rodent found in the southeastern United States. Coat color in the beach mouse is variable, from dark brown to blonde (Figure 1). A pigment called eumelanin is responsible for some of the diversity in mouse coat color. The MC1R gene, located on chromosome 8, plays a major role in the synthesis of eumelanin. There are two alleles of MC1R: R allele. Results in a functional MC1R protein that leads to stimulation of pigment production. This allele is found in dark colored mice. C allele. Results in a non-functional MC1R protein. Pigment production is, as a result, not stimulated. This allele is found in light colored mice. Figure 1. Beach mouse with light fur (left) and dark (right). These mice are hunted by visual predators like owls and fox. The distribution of coat color is not random. Beach mice with dark fur are found further inland, on dark brown soils while mice with light fur are found on beaches, where the sand is light brown.…arrow_forwardThe beach mouse (Peromyscus polionotus) is a small rodent found in the southeastern United States. Coat color in the beach mouse is variable, from dark brown to blonde (Figure 1). A pigment called eumelanin is responsible for some of the diversity in mouse coat color. The MC1R gene, located on chromosome 8, plays a major role in the synthesis of eumelanin. There are two alleles of MC1R: R allele. Results in a functional MC1R protein that leads to stimulation of pigment production. This allele is found in dark colored mice. C allele. Results in a non-functional MC1R protein. Pigment production is, as a result, not stimulated. This allele is found in light colored mice. Figure 1. Beach mouse with light fur (left) and dark (right). These mice are hunted by visual predators like owls and fox. The distribution of coat color is not random. Beach mice with dark fur are found further inland, on dark brown soils while mice with light fur are found on beaches, where the sand is…arrow_forwardCat 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. State the genotype of the male and the female.arrow_forward
- 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:arrow_forwardExplain 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_forwardIn Drosophila subobscura, the presence of a recessive gene called grandchildless (gs) causes the offspring of homozygous females, but not those of homozygous males, to be sterile. Can you offer an explanation as to why females and not males are affected by the mutant gene?arrow_forward
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