Textbook Question
A wild-type Drosophila male and female are crossed, producing 324 female progeny and 161 male progeny. All their progeny are wild type.
Propose a genetic hypothesis to explain these data.
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Ch. 3 - Cell Division and Chromosome Heredity
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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Table of contents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
Chapter 3, Problem 26
In humans, SRY is located near a pseudoautosomal region (PAR) of the Y chromosome, a region of homology between the X and Y chromosomes that allows them to synapse during meiosis in males and is a region of crossover between the chromosomes. The diagram below shows SRY in relation to the pseudoautosomal region.
About 1 in every 25,000 newborn infants is born with sex reversal; the infant is either an apparent male but with two X chromosomes or an apparent female but with an X and a Y chromosome. Explain the origin of sex reversal in human males and females involving the SRY gene. (Hint: See Experimental Insight 3.1 for a clue about the mutational mechanism.)
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Understand the role of the SRY gene: The SRY (Sex-determining Region Y) gene is located on the Y chromosome near the pseudoautosomal region (PAR). It is responsible for initiating male sex determination by triggering the development of testes.
Analyze the diagram: The image shows the SRY gene positioned close to the PAR region on the Y chromosome. The PAR region is homologous between the X and Y chromosomes, allowing them to pair and undergo crossover during meiosis.
Consider the mechanism of sex reversal: During meiosis in males, crossover events can occur between the X and Y chromosomes in the PAR region. If the crossover extends beyond the PAR region and includes the SRY gene, the SRY gene can be translocated to the X chromosome.
Explain the outcome of SRY translocation: If the SRY gene is translocated to the X chromosome, an individual with two X chromosomes (XX) may develop as a phenotypic male due to the presence of the SRY gene. Conversely, if the Y chromosome loses the SRY gene, an individual with an X and Y chromosome (XY) may develop as a phenotypic female.
Summarize the mutational mechanism: Sex reversal in humans can occur due to errors in meiotic crossover that result in the translocation of the SRY gene to the X chromosome or its deletion from the Y chromosome. This explains the origin of apparent males with XX chromosomes and apparent females with XY chromosomes.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
SRY Gene
The SRY (Sex-determining Region Y) gene is crucial for male sex determination in humans. Located on the Y chromosome, it encodes a protein that triggers the development of male characteristics by initiating the formation of testes, which produce male hormones. Mutations or deletions in the SRY gene can lead to sex reversal, where individuals may have a male phenotype despite having two X chromosomes.
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Mapping Genes
Pseudoautosomal Region (PAR)
The pseudoautosomal region (PAR) is a small region on the X and Y chromosomes that shares homology, allowing these chromosomes to pair during meiosis. This region is essential for proper segregation of sex chromosomes during gamete formation. The presence of PAR facilitates genetic recombination, which can influence the inheritance of sex-linked traits and contribute to variations in sex determination.
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00:30Regions of X Chromosomes
Sex Reversal
Sex reversal refers to a condition where an individual’s phenotypic sex does not match their chromosomal sex. In humans, this can occur when individuals with XY chromosomes develop female characteristics or those with XX chromosomes develop male characteristics. Such discrepancies often arise from mutations in the SRY gene or other genes involved in sex determination, leading to atypical development of sexual characteristics.
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Related Practice
Textbook Question
In an 1889 book titled Natural Inheritance (Macmillan, New York), Francis Galton, who investigated the inheritance of measurable (quantitative) traits, formulated a law of 'ancestral inheritance.' The law stated that individuals inherit approximately one-half of their genetic traits from each parent, about one-quarter of the traits from each grandparent, one-eighth from each great grandparent, and so on. In light of the chromosome theory of heredity, argue either in favor of Galton's law or against it.
Textbook Question
In Drosophila, the X-linked echinus eye phenotype disrupts formation of facets and is recessive to wild-type eye. Autosomal recessive traits vestigial wing and ebony body assort independently of one another. Examine the progeny from the three crosses shown below, and identify the genotype of parents in each cross.
Textbook Question
Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.
What is the probability that the first son of a man whose brother has Lesch–Nyhan syndrome will be affected?
Textbook Question
Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.
What is the probability that the first son of a woman whose brother has Lesch–Nyhan syndrome will be affected?
Textbook Question
Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.
If the first son of the woman described in (a) is affected, what is the probability that her second son is affected?
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