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Ch. 14 - Mendel and the Gene
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
Chapter 14, Problem 16b

You have crossed two Drosophila melanogaster individuals that have long wings and red eyes—the wild-type phenotype. In the progeny, curved wings and lozenge eyes mutant phenotypes appear as follows. Is the lozenge-eyed allele autosomal recessive, autosomal dominant, sex-linked recessive, or sex-linked dominant?

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1
Examine the phenotypic ratios in the progeny. Notice that both males and females exhibit the lozenge eyes phenotype, which suggests that the trait is not sex-limited.
Calculate the total number of progeny with lozenge eyes: 300 males with long wings and lozenge eyes + 100 males with curved wings and lozenge eyes = 400 males with lozenge eyes.
Compare the number of lozenge-eyed males to the total number of males: 400 lozenge-eyed males out of 800 total males (300 long wings, red eyes + 100 curved wings, red eyes + 300 long wings, lozenge eyes + 100 curved wings, lozenge eyes).
Since lozenge eyes appear in both males and females, and the ratio of lozenge-eyed individuals is approximately 1:1 in males, consider whether the trait could be sex-linked. In sex-linked traits, males often show the phenotype more frequently if it is recessive.
Conclude that the lozenge-eyed allele is likely sex-linked recessive, as it appears in a significant portion of the male progeny, consistent with X-linked recessive inheritance patterns where males express the trait if they inherit the recessive allele.

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Key Concepts

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

Drosophila melanogaster Genetics

Drosophila melanogaster, commonly known as the fruit fly, is a model organism in genetics. Its simple genetic structure and short life cycle make it ideal for studying inheritance patterns. Traits such as wing shape and eye color are often used to illustrate Mendelian genetics, where dominant and recessive alleles determine phenotypic expression.
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Phenotype and Genotype

Phenotype refers to the observable characteristics of an organism, such as wing shape and eye color, while genotype refers to the genetic makeup that determines these traits. In this scenario, the wild-type phenotype (long wings and red eyes) is contrasted with mutant phenotypes (curved wings and lozenge eyes), which can help infer the inheritance pattern of the alleles involved.
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Genotype & Phenotype

Inheritance Patterns

Inheritance patterns describe how traits are passed from parents to offspring. In this case, determining whether the lozenge-eyed allele is autosomal recessive, autosomal dominant, sex-linked recessive, or sex-linked dominant requires analyzing the ratios of phenotypes in the progeny. The presence of specific phenotypes in males and females can indicate whether the trait is linked to sex chromosomes or is inherited through autosomes.
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Related Practice
Textbook Question

The blending inheritance hypothesis proposed that the genetic material from parents is mixed in the offspring. As a result, traits of offspring and later descendants should lie between the phenotypes of parents. Mendel, in contrast, proposed that genes are discrete and that their integrity is maintained in the offspring and in subsequent generations. Suppose the year is 1890. You are a horse breeder who has just read Mendel's paper. You don't believe his results, however, because you often work with cremello (very light-colored) and chestnut (reddish-brown) horses. You know that when you breed a cremello individual from a pure-breeding line with a chestnut individual from a pure-breeding line, the offspring are palomino—meaning they have an intermediate (golden-yellow) body color. What additional cross would you do to test whether Mendel's model is valid in the case of genes for horse color? According to his model, what offspring phenotype frequencies would you get from your experimental cross? Explain why your cross would test Mendel's model versus blending inheritance.

Textbook Question

Two mothers give birth to sons at the same time in a busy hospital. The son of couple 1 is afflicted with hemophilia A, which is a recessive X-linked disease. Neither parent has the disease. Couple 2 has a normal son even though the father has hemophilia A. The two couples sue the hospital in court, claiming that a careless staff member swapped their babies at birth. You appear in court as an expert witness. What do you tell the jury? Make a diagram that you can submit to the jury.

Textbook Question

You have crossed two Drosophila melanogaster individuals that have long wings and red eyes—the wild-type phenotype. In the progeny, curved wings and lozenge eyes mutant phenotypes appear as follows According to these data, is the curved-wing allele autosomal recessive, autosomal dominant, sex-linked recessive, or sex-linked dominant?

Textbook Question

You have crossed two Drosophila melanogaster individuals that have long wings and red eyes—the wild-type phenotype. In the progeny, curved wings and lozenge eyes mutant phenotypes appear as follows: What is the genotype of the female parent?

Textbook Question

You have crossed two Drosophila melanogaster individuals that have long wings and red eyes—the wild-type phenotype. In the progeny, curved wings and lozenge eyes mutant phenotypes appear as follows: What is the genotype of the male parent?