Essentials of Genetics (9th Edition) - Standalone book
9th Edition
ISBN: 9780134047799
Author: William S. Klug, Michael R. Cummings, Charlotte A. Spencer, Michael A. Palladino
Publisher: PEARSON
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Chapter 5, Problem 1PDQ
HOW DO WE KNOW?
In this chapter, we have focused on sex differentiation, sex chromosomes, and genetic mechanisms involved in sex determination. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, you should answer the following fundamental questions:
(a) How do we know that in humans the X chromosomes play no role in sex determination, while the Y chromosome causes maleness and its absence causes femaleness?
(b) How did we originally (in the late 1940s) analyze the sex ratio at conception in humans, and how has our approach to studying this issue changed in 2015?
(c) How do we know that X chromosomal inactivation of either the paternal or maternal homolog is a random event during early development in mammalian females?
(d) How do we know that Drosophila utilizes a different sex-determination mechanism than mammals, even though it has the same sex-chromosome compositions in males and females?
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With relevance to sex determination in humans, discuss: i) X chromosome inactivation; and ii) Testicular feminization
Provide detail examples.
Most sexual organisms are either male or female though some are hermaphroditic. In human beings and Drosophila (fruitfly), the sex of an individual is determined by the kind of sex chromosomes they possess. Males have two types of chromosomes, a big chromosome X and a small chromosome Y while females have only one kind, 2X or XX. The X and Y chromosomes segregate during the formation of mature spermatozoa (sprematogenesis) so that a mature sperm contains only either X or Y.
What is the probability of getting an X-bearing sperm? A Y-bearing sperm? How many kinds of ova as to the kind of sex chromosome present can be produced? Determine the probability of getting a boy or girl. Show your calculations.
Most sexual organisms are either male or female though some are hermaphroditic. In human beings and Drosophila (fruitfly), the sex of an individual is determined by the kind of sex chromosomes they possess. Males have two types of chromosomes, a big chromosome X and a small chromosome Y while females have only one kind, 2X or XX. The X and Y chromosomes segregate during the formation of mature spermatozoa (sprematogenesis) so that a mature sperm contains only either X or Y.
What is the probability of getting an X-bearing sperm? A Y-bearing sperm? How many kinds of ova as to the kind of sex chromosome present can be produce? Determine the probability of getting a boy or girl. Show your calculations.
Chapter 5 Solutions
Essentials of Genetics (9th Edition) - Standalone book
Ch. 5 -
CASE STUDY | Doggone it!
A dog breeder...Ch. 5 - CASE STUDY| Doggone it! A dog breeder discovers...Ch. 5 - CASE STUDY| Doggone it! A dog breeder discovers...Ch. 5 -
CASE STUDY | Doggone it!
A dog breeder...Ch. 5 - HOW DO WE KNOW? In this chapter, we have focused...Ch. 5 - Review the Chapter Concepts list on p. 84. These...Ch. 5 - As related to sex determination, what is meant by...Ch. 5 -
4. Contrast the life cycle of a plant such as...Ch. 5 - Prob. 5PDQCh. 5 -
6. Describe the major difference between sex...
Ch. 5 - How do mammals, including humans, solve the...Ch. 5 -
8. What specific observations (evidence) support...Ch. 5 - Describe how nondisjunction in human female...Ch. 5 -
10. An insect species is discovered in which the...Ch. 5 -
11. Given your answers to Problem 10, is it...Ch. 5 - When cows have twin calves of unlike sex...Ch. 5 -
13. An attached-X female fly, XXY (see the...Ch. 5 -
14. Assume that on rare occasions the attached X...Ch. 5 - It is believed that any male-determining genes...Ch. 5 -
16. What is a Barr body, and where is it found...Ch. 5 - Indicate the expected number of Barr bodies in...Ch. 5 - Define the Lyon hypothesis.Ch. 5 - Can the Lyon hypothesis be tested in a human...Ch. 5 - Predict the potential effect of the Lyon...Ch. 5 -
21. Cat breeders are aware that kittens...Ch. 5 -
22. What does the apparent need for dosage...Ch. 5 - In mice, the Sry gene (see Section 5.2) is located...Ch. 5 - The genes encoding the red- and...Ch. 5 - In mice, the X-linked dominant mutation Testicular...Ch. 5 -
26. Shown here are graphs that plot the...Ch. 5 -
27. In chickens, a key gene involved in sex...
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- The Amami spiny rat (Tokudaia osimensis) lacks a Y chromosome, yet scientists at Hokkaido University in Japan have reported that key sex-determining genes continue to be expressed in this species. Provide possible explanations for why male differentiation can still occur in this mammalian species despite the absence of a Y chromosome.arrow_forwardWhat is the general role of the gene product of SRY in human sex determination? Also, on which chromosome(s) is the SRY gene normally located?arrow_forwardAssume that you were examining a first polar body and noted that it had one copy (dyad) of each chromosome except chromosome 21. Chromosome 21 was completely absent. What would you expect to be the chromosome 21 complement (only with respect to chromosome 21) in the secondary oocyte? What consequences are likely in the resulting zygote if the secondary oocyte was fertilized?arrow_forward
- If the amount (mass) of DNA in a diploid cell during G1 phase prior to meiosis I is 8 pg (picograms), how much DNA would be present in a daughter cell immediately following: A) meiosis I? B) meiosis II? (for your information, this cell will function as a gamete) HINT: Go through the process of meiosis one step at a time. DNA replication would double the amount of DNA in the cell, cell division divides the DNA into two daughter cells.arrow_forwardSexual reproduction results in offspring that are genetically different from one another and from their parents. Describe four mechanisms that produce this genetic variation. Do any of these mechanisms occur in asexualreproduction?arrow_forwardWhy is aneuploidy of the sex chromosomes less debilitating than aneuploidy of even the smallest autosomes? (Note: multiple responses are correct, please choose the best answer(s)) Select one or more: Only one X chromosome is required at any given time. Additional X chromosomes (as in females) are inactivated in most cells except for gametes Dosage compensation requires that all excess chromosomes (i.e. 2 or more) are activated at all times during the cell cycle The Y chromosome carries a number of critical genes involved in spermatogenesis and sex development. Therefore, having two copies of the Y chromosome results in the overproduction of sperm and increased fertility The Y chromosome carries a number of critical genes required for spermatogenesis and sex development, but very few other genes. Therefore, having two copies of the Y chromosome has minimal impact on the balance of gene expressionarrow_forward
- With reference to sex determination in humans, discuss: i) X chromosome inactivation; and ii) Testicular feminizationarrow_forwardDraw a schematic diagram showing spermatogenesis vis-à-vis oogenesis. Label the stage of development and chromosome number of daughter cells at the following levels of maturation: (a) mitotic proliferation (b) meiosis I and II (c) maturation. Table 2: Spermatogenesis vis-à-vis Oogenesis Spermatogenesis Oogenesisarrow_forwardAs we have focused on sex differentiation, sex chromosomes, and genetic mechanisms involved in sex determination. At the same time, we found manyopportunities to consider the methods and reasoning by whichmuch of this information was acquired. From the explanationsgiven in the chapter, you should answer the following fundamentalquestion: How do we know that X chromosomal inactivation of eitherthe paternal or maternal homolog is a random event duringearly development in mammalian females?arrow_forward
- The mouse haploid genome contains about 2.9 × 109 nucleotide pairs of DNA. Indicate how many nucleotide pairs of DNA are present in each of the following mouse cells: (a) somatic cell, (b) sperm cell, (c) fertilized egg,(d) primary oocyte, (e) first polar body, (f) secondary spermatocyte.arrow_forwardWhat are the non-random events that occur during sexual reproduction (post-meiosis) in humans? Please be specific on naming the events.arrow_forwardSex-reversed females with XY were found to be missing SRY gene on their Y chromosomes, while sex-reversed males with XX were found to carry a portion of a Y chromosome that has the SRY gene. What can you conclude from these two cases? 1.Sex determination depends primarily on the combination of sex chromosomes and the presence of SRY gene. 2.X and Y chromosomes can’t pair up during meiosis because they are not true homologous chromosomes. 3.Nonreciprocal crossover could result in translocation of the SRY gene between X and Y chromosome. 4. The SRY gene has a key role to determine maleness. 5.The Y chromosome contains a gene that determine maleness.arrow_forward
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