Textbook Question
Indicate the expected number of Barr bodies in interphase cells of individuals with Klinefelter syndrome, Turner syndrome, and karyotypes 47, XYY, 47, XXX, and 48, XXXX.
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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 20
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.
Verified step by step guidance1
Understand the Lyon hypothesis, which states that in female mammals, one of the two X chromosomes in each cell is randomly inactivated during early embryonic development, leading to a mosaic pattern of X-linked gene expression.
Recognize that the female in question is heterozygous for the X-linked red-green color blindness trait, meaning she has one X chromosome with the normal allele and one X chromosome with the allele for red-green color blindness.
Consider that due to random X-inactivation, some retinal cells will express the normal allele (from the active X chromosome with the normal gene), while others will express the allele for color blindness (from the active X chromosome carrying the mutation).
Predict that this mosaic expression in the retina could lead to a patchy or mixed population of cone cells, some functioning normally and others deficient in red-green color perception, potentially resulting in a variable or partial color vision phenotype.
Conclude that the overall effect on the female's color vision depends on the proportion and distribution of cells expressing each X chromosome, which can vary between individuals due to the randomness of X-inactivation.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Lyon Hypothesis (X-Chromosome Inactivation)
The Lyon hypothesis explains that in female mammals, one of the two X chromosomes in each cell is randomly inactivated during early embryonic development. This process creates a mosaic pattern of gene expression, where some cells express genes from the maternal X and others from the paternal X, affecting traits linked to the X chromosome.
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X-Inactivation
X-Linked Red-Green Color Blindness
Red-green color blindness is a common X-linked recessive trait caused by mutations in genes coding for photopigments in the retina. Males with the mutation on their single X chromosome express the trait, while females must be homozygous to be fully color blind; heterozygous females are typically carriers with normal vision but can show mosaic expression.
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09:30X-Inactivation
Mosaicism in Retinal Cells
Due to X-chromosome inactivation, heterozygous females for X-linked traits like red-green color blindness have retinal cells expressing either the normal or mutant allele. This mosaicism can lead to patches of retina with normal color vision and patches with deficient color perception, potentially affecting overall color discrimination.
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Related Practice
Textbook Question
Define the Lyon hypothesis.
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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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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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