Textbook Question
Compare and contrast broad sense heritability and narrow sense heritability, giving an example of each measurement and identifying how the measurement is used.
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Ch. 4 - Gene Interaction
Chapter 4, Problem 6
In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color—with two alleles, y⁺ for gray body and y for yellow body—resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w⁺ for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f⁺ for normal bristles and f for forked bristles, is located at map position 56.7. At each locus the wild-type allele is dominant over the mutant allele.
In a cross involving these three X-linked genes, do you expect any gene pair(s) to show genetic linkage? Explain your reasoning.
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Identify the map positions of the genes on the X chromosome: y⁺/y at 0.0, w⁺/w at 1.5, and f⁺/f at 56.7.
Understand that genetic linkage refers to genes located close to each other on the same chromosome, which tend to be inherited together.
Calculate the distance between each pair of genes: y⁺/y and w⁺/w, y⁺/y and f⁺/f, and w⁺/w and f⁺/f.
Recognize that genes closer than 50 map units apart are likely to show genetic linkage due to reduced recombination frequency.
Determine which gene pairs are within 50 map units of each other to assess potential genetic linkage.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Genetic Linkage
Genetic linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together during meiosis. This occurs because linked genes are less likely to be separated by recombination events. The closer the genes are on the chromosome, the stronger the linkage, which can be measured in map units (m.u.). In the context of the question, analyzing the distances between the genes helps determine if they are likely to be linked.
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07:33
Chi Square and Linkage
Map Units (m.u.)
Map units, or centimorgans (cM), are a unit of measurement for genetic linkage that reflects the distance between genes on a chromosome. One map unit corresponds to a 1% chance of recombination occurring between two genes during meiosis. In the provided scenario, the distances between the genes (0.0 to 1.5 m.u. for body color and eye color, and 1.5 to 56.7 m.u. for eye color and bristle form) indicate the likelihood of linkage, with smaller distances suggesting stronger linkage.
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09:09Mapping Genes
Dominance and Alleles
Dominance in genetics refers to the relationship between alleles, where one allele (the dominant) masks the expression of another (the recessive) in a heterozygous individual. In the question, the wild-type alleles (y⁺, w⁺, f⁺) are dominant over their respective mutant alleles (y, w, f). Understanding dominance is crucial for predicting phenotypic outcomes in crosses, especially when considering how linked genes may affect inheritance patterns.
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04:37Variations on Dominance
Related Practice
Textbook Question
In a cross of two pure-breeding lines of tomatoes producing different fruit sizes, the variance in grams (g) of fruit weight in the F₁ is 2.25 g and the variance among the F₂ is 5.40 g. Determine the genetic and environmental variance (VG and VE) for the trait and the broad sense heritability of the trait.
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Textbook Question
Describe the difference between continuous phenotypic variation and discontinuous variation. Explain how polygenic inheritance could be the basis of a trait showing continuous phenotypic variation. Explain how polygenic inheritance can be the basis of a threshold trait.
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Textbook Question
In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color—with two alleles, y⁺ for gray body and y for yellow body—resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w⁺ for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f⁺ for normal bristles and f for forked bristles, is located at map position 56.7. At each locus the wild-type allele is dominant over the mutant allele.
Do you expect any of these gene pair(s) to assort independently? Explain your reasoning.
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Textbook Question
In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color—with two alleles, y⁺ for gray body and y for yellow body—resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w⁺ for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f⁺ for normal bristles and f for forked bristles, is located at map position 56.7. At each locus the wild-type allele is dominant over the mutant allele.
A wild-type female fruit fly with the genotype y⁺w⁺f/ywf⁺ is crossed to a male fruit fly that has yellow body, white eye, and forked bristles. Predict the frequency of each progeny phenotype class produced by this mating.
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Textbook Question
In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color—with two alleles, y⁺ for gray body and y for yellow body—resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w⁺ for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f⁺ for normal bristles and f for forked bristles, is located at map position 56.7. At each locus the wild-type allele is dominant over the mutant allele.
Explain how each of the predicted progeny classes is produced.
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