An attached-X female fly, XXY (see the "Insights and Solutions" box), expresses the recessive X-linked white-eye phenotype. It is crossed to a male fly that expresses the X-linked recessive miniature wing phenotype. Determine the outcome of this cross in terms of sex, eye color, and wing size of the offspring.

Short Answer

Expert verified
Answer: The offspring's phenotypes will be: 1. Female flies with wild-type eyes and miniature wings. 2. Male flies with white eyes and wild-type wings. 3. Male flies with wild-type eyes and miniature wings.

Step by step solution

01

Write down the genotypes of the parents

The female fly has attached-X chromosomes, with genotype XXY = XX^wY (the superscript "w" indicates the white-eye allele). The male fly has a genotype XY with one miniature wing allele, which can be represented as XmY.
02

Perform the cross

To find out the possible combinations of alleles in the offspring, we should perform the cross between the female and the male flies. This can be done by creating a Punnett square. We should focus on the possible combinations of X and Y chromosomes first. The Punnett square will look like this: X^w X^w Y Xm X^wXm X^wXm XmY Y X^wY X^wY YY Note that since YY is not a viable genotype for flies, we can ignore this outcome.
03

Determine the sex, eye color, and wing size of the offspring

Now, we can analyze the resulting genotypes to determine the sex, eye color, and wing size of the offspring. 1. X^wXm: This offspring is female (XX), it will have wild-type eyes (X-linked recessive trait, one dominant allele is enough), and miniature wings (X-linked recessive trait, two recessive alleles required for a female). 2. X^wY: This offspring is male (XY), it will have white eyes (X-linked recessive trait, only one allele required for a male), and wild-type wings (X-linked recessive trait, one dominant allele is enough). 3. XmY: This offspring is male (XY), it will have wild-type eyes (X-linked recessive trait, one dominant allele is enough), and miniature wings (X-linked recessive trait, only one allele required for a male).
04

Summarize the results

In the offspring of this cross between a female fly with the attached-X condition and a recessive X-linked white-eye phenotype, and a male fly with the X-linked recessive miniature wing phenotype, we can expect the following combinations: 1. Female flies with wild-type eyes and miniature wings. 2. Male flies with white eyes and wild-type wings. 3. Male flies with wild-type eyes and miniature wings.

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Most popular questions from this chapter

Describe how nondisjunction in human female gametes can give rise to Klinefelter and Turner syndrome offspring following fertilization by a normal male gamete.

In Drosophila, an individual female fly was observed to be of the \(\mathrm{XXY}\) chromosome complement (normal autosomal complement) and to have white eyes as contrasted with the normal red eye color of wild type. The female's father had red eyes, and the mother had white eyes. Knowing that white eyes are X-linked and recessive, present an explanation for the genetic and chromosomal constitution of the XXY, whiteeyed individual. It is important that you state in which parent and at what stage the chromosomal event occurred that caused the genetic and cytogenetic abnormality.

In this chapter, we have focused on sex differentiation, sex chro- mosomes, and genetic mechanisms involved in sex determination. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, you should answer the following fundamental questions: (a) How do we know that in humans the X chromosomes play no role in sex determination, while the Y chromosome causes maleness and its absence causes femaleness? (b) How did we originally (in the late 1940 s) analyze the sex ratio at conception in humans, and how has our approach to studying this issue changed in \(2015 ?\) (c) How do we know that \(X\) chromosomal inactivation of either the paternal or maternal homolog is a random event during early development in mammalian females? (d) How do we know that Drosophila utilizes a different sexdetermination mechanism than mammals, even though it has the same sex-chromosome compositions in males and females?

What is a Barr body, and where is it found in a cell?

What specific observations (evidence) support the conclusions about sex determination in Drosophila and humans?

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