Textbook Question
Can the Lyon hypothesis be tested in a human female who is homozygous for one allele of the X-linked G6PD gene? Why, or why not?
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Ch. 5 - Sex Determination and Sex Chromosomes
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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Table of contents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Chapter 5, Problem 22
What does the apparent need for dosage compensation mechanisms suggest about the expression of genetic information in normal diploid individuals?
Verified step by step guidance1
Understand that dosage compensation mechanisms are biological processes that balance the expression of genes between individuals with different numbers of sex chromosomes, such as males (XY) and females (XX).
Recognize that in normal diploid individuals, each gene is typically present in two copies (alleles), one from each parent, and these copies are usually expressed at similar levels.
Consider that the need for dosage compensation implies that without such mechanisms, the difference in gene copy number (for example, between the single X chromosome in males and two X chromosomes in females) would lead to unequal gene expression levels.
Conclude that this suggests gene expression is sensitive to gene dosage, meaning the amount of gene product produced depends on the number of gene copies present.
Therefore, dosage compensation mechanisms are necessary to equalize gene expression levels, ensuring that genetic information is expressed in a balanced way despite differences in chromosome number.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Dosage Compensation
Dosage compensation is a biological mechanism that balances the expression of genes between individuals with differing numbers of sex chromosomes, such as males (XY) and females (XX). It ensures that genes on the sex chromosomes are expressed at similar levels despite differences in chromosome number, preventing harmful imbalances in protein production.
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00:52
Purpose of X Inactivation
Gene Expression Regulation in Diploids
In diploid organisms, each gene typically has two copies (alleles), one from each parent. Proper regulation of gene expression is crucial to maintain cellular function and organismal development, as imbalances in gene dosage can lead to abnormal phenotypes or diseases.
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27:36Diploid Genetics
Impact of Gene Dosage on Phenotype
Gene dosage refers to the number of copies of a gene present in a cell. Variations in gene dosage can affect the amount of gene product produced, influencing phenotype. Dosage compensation mechanisms highlight the importance of maintaining balanced gene expression to avoid detrimental effects caused by over- or under-expression.
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Related Practice
Textbook Question
Predict the potential effect of the Lyon hypothesis on the retina of a human female heterozygous for the X-linked red-green color blindness trait.
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Textbook Question
Cat breeders are aware that kittens expressing the X-linked calico coat pattern and tortoiseshell pattern are almost invariably females. Why are they certain of this?
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Textbook Question
In mice, the Sry gene is located on the Y chromosome very close to one of the pseudoautosomal regions that pairs with the X chromosome during male meiosis. Given this information, propose a model to explain the generation of unusual males who have two X chromosomes (with an Sry-containing piece of the Y chromosome attached to one X chromosome).
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Textbook Question
The genes encoding the red- and green-color-detecting proteins of the human eye are located next to one another on the X chromosome and probably evolved from a common ancestral pigment gene. The two proteins demonstrate 76 percent homology in their amino acid sequences. A normal-visioned woman (with both genes present on each of her two X chromosomes) has a red-color-blind son who was shown to have one copy of the green-detecting gene and no copies of the red-detecting gene. Devise an explanation for these observations at the chromosomal level (involving meiosis).
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Textbook Question
In mice, the X-linked dominant mutation Testicular feminization (Tfm) eliminates the normal response to the testicular hormone testosterone during sexual differentiation. An XY mouse bearing the Tfm allele on the X chromosome develops testes, but no further male differentiation occurs—the external genitalia of such an animal are female. From this information, what might you conclude about the role of the Tfm gene product and the X and Y chromosomes in sex determination and sexual differentiation in mammals? Can you devise an experiment, assuming you can 'genetically engineer' the chromosomes of mice, to test and confirm your explanation?
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