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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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Ch. 5 - Sex Determination and Sex Chromosomes
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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TOC.tableOfContents
- 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
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Non è quello che usi tu?Cambia libro di testo
Capitolo 5, Problema 19
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?
Guida verificata passo dopo passo1
Step 1: Understand the Lyon hypothesis, which states that in female mammals, one of the two X chromosomes is randomly inactivated in each cell early in development, leading to dosage compensation between males (XY) and females (XX).
Step 2: Recognize that the Lyon hypothesis can be tested by observing phenotypic mosaicism in heterozygous females for an X-linked gene, where different cells express different alleles depending on which X chromosome is inactivated.
Step 3: Consider the genetic status of the female in question: she is homozygous for one allele of the X-linked G6PD gene, meaning both X chromosomes carry the same allele.
Step 4: Analyze the consequence of homozygosity: since both X chromosomes have the same allele, X-inactivation will not produce any phenotypic mosaicism because all cells express the same allele regardless of which X is inactivated.
Step 5: Conclude that the Lyon hypothesis cannot be effectively tested in this homozygous female using the G6PD gene, because the lack of allelic variation prevents observation of differential expression due to X-inactivation.
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Lyon Hypothesis (X-Chromosome Inactivation)
The Lyon hypothesis proposes that in female mammals, one of the two X chromosomes is randomly inactivated in each cell early in development, leading to dosage compensation between males and females. This inactivation is stable and results in mosaic expression of X-linked genes in heterozygous females.
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09:30
X-Inactivation
X-Linked Genes and Allelic Variation
X-linked genes, like G6PD, are located on the X chromosome. Females have two alleles for these genes, which can be different (heterozygous) or the same (homozygous). The presence of different alleles allows observation of differential expression due to X inactivation.
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07:56Sex-Linked Genes
Testing the Lyon Hypothesis in Homozygous Females
In a female homozygous for one allele of an X-linked gene, both X chromosomes carry the same allele, so X inactivation cannot be detected by phenotypic differences. Therefore, the Lyon hypothesis cannot be directly tested in such individuals because there is no observable mosaicism.
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10:35Human Sex Chromosomes
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