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Ch. 5 - Chromosome Mapping in Eukaryotes
All textbooksKlug 12th EditionCh. 5 - Chromosome Mapping in EukaryotesProblem 15
Chapter 5, Problem 15

Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The F₁ females were wild type for all three traits, while the F₁ males expressed the yellow-body and white-eye traits. The cross was carried to an F₂ progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed. Phenotype Male Offspring y + ct 9 + w + 6 y w ct 90 + + + 95 + + ct 424 y w + 376 y + + 0 + w ct 0 Construct a map, assuming that white is at locus 1.5 on the X chromosome.

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Identify the parental genotypes and phenotypes: The female is yellow-bodied, white-eyed, and has normal wings (y w +), while the male has normal body and eyes but cut wings (+ + ct).
Determine the F₁ generation phenotypes: F₁ females are wild type for all traits (+ + +), and F₁ males express yellow body and white eyes (y w +).
Analyze the F₂ male offspring data to identify recombinant and non-recombinant phenotypes. Non-recombinant phenotypes are those that resemble the parental types, while recombinant phenotypes result from crossing over.
Calculate the recombination frequencies between the genes by using the formula: Recombination frequency = (Number of recombinant offspring / Total number of offspring) x 100. This will help determine the distances between the genes.
Construct the genetic map by placing the genes on the X chromosome based on the calculated recombination frequencies, starting with the white gene at locus 1.5.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

X-linked Inheritance

X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. In Drosophila, males have one X chromosome and one Y chromosome, while females have two X chromosomes. This means that recessive traits linked to the X chromosome are more likely to be expressed in males, as they have no second X chromosome to mask the recessive allele. Understanding this concept is crucial for analyzing the inheritance patterns in the given cross.
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X-Inactivation

Phenotypic Ratios

Phenotypic ratios are the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this case, the phenotypic ratios of male offspring provide insights into the linkage and recombination frequencies of the genes involved. By analyzing these ratios, one can infer the genetic distances between the loci on the X chromosome, which is essential for constructing a genetic map.
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Mutations and Phenotypes

Genetic Mapping

Genetic mapping is the process of determining the relative positions of genes on a chromosome based on recombination frequencies. In this scenario, the data from the F₂ progeny allows for the calculation of distances between the genes yellow, white, and cut. By assuming a specific position for one gene (white at locus 1.5), one can use the observed phenotypic ratios to estimate the positions of the other genes, thereby constructing a genetic map.
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Mapping Overview
Related Practice
Textbook Question
In Drosophila, a cross was made between females—all expressing the three X-linked recessive traits scute bristles (sc), sable body (s), and vermilion eyes (v)—and wild-type males. In the F₁, all females were wild type, while all males expressed all three mutant traits. The cross was carried to the F₂ generation, and 1000 offspring were counted, with the results shown in the following table. Phenotype Offspring sc s v 314 + + + 280 + s v 150 sc + + 156 sc + v 46 + s + 30 sc s + 10 + + v 14 No determination of sex was made in the data. Are there more or fewer double crossovers than expected?

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Textbook Question
In Drosophila, a cross was made between females—all expressing the three X-linked recessive traits scute bristles (sc), sable body (s), and vermilion eyes (v)—and wild-type males. In the F₁, all females were wild type, while all males expressed all three mutant traits. The cross was carried to the F₂ generation, and 1000 offspring were counted, with the results shown in the following table. Phenotype Offspring sc s v 314 + + + 280 + s v 150 sc + + 156 sc + v 46 + s + 30 sc s + 10 + + v 14 No determination of sex was made in the data. Calculate the coefficient of coincidence. Does it represent positive or negative interference?
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Textbook Question
Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The F₁ females were wild type for all three traits, while the F₁ males expressed the yellow-body and white-eye traits. The cross was carried to an F₂ progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed. Phenotype Male Offspring y + ct 9 + w + 6 y w ct 90 + + + 95 + + ct 424 y w + 376 y + + 0 + w ct 0 Diagram the genotypes of the F₁ parents.
357
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Textbook Question
Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The F₁ females were wild type for all three traits, while the F₁ males expressed the yellow-body and white-eye traits. The cross was carried to an F₂ progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed. Phenotype Male Offspring y + ct 9 + w + 6 y w ct 90 + + + 95 + + ct 424 y w + 376 y + + 0 + w ct 0 Could the F₂ female offspring be used to construct the map? Why or why not?
503
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Textbook Question
Another cross in Drosophila involved the recessive, X-linked genes yellow (y), white (w), and cut (ct). A yellow-bodied, white-eyed female with normal wings was crossed to a male whose eyes and body were normal but whose wings were cut. The F₁ females were wild type for all three traits, while the F₁ males expressed the yellow-body and white-eye traits. The cross was carried to an F₂ progeny, and only male offspring were tallied. On the basis of the data shown here, a genetic map was constructed. Phenotype Male Offspring y + ct 9 + w + 6 y w ct 90 + + + 95 + + ct 424 y w + 376 y + + 0 + w ct 0 Were any double-crossover offspring expected?
402
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Textbook Question
In Drosophila, Dichaete (D) is a mutation on chromosome III with a dominant effect on wing shape. It is lethal when homozygous. The genes ebony body (e) and pink eye (p) are recessive mutations on chromosome III. Flies from a Dichaete stock were crossed to homozygous ebony, pink flies, and the F₁ progeny, with a Dichaete phenotype, were backcrossed to the ebony, pink homozygotes. Using the results of this backcross shown in the table, Phenotype Number Dichaete 401 ebony, pink 389 Dichaete, ebony 84 pink 96 Dichaete, pink 2 ebony 3 Dichaete, ebony, pink 12 wild type 13 What is the sequence and interlocus distance between these three genes?
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