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Chapter 5: Problem 19

Can the Lyon hypothesis be tested in a human female who is homozygous for one allele of the X-linked G6PD gene? Why, or why not?

Short Answer

Expert verified
Explain your reasoning. Answer: No, the Lyon hypothesis cannot be tested in a human female who is homozygous for one allele of the X-linked G6PD gene. This is because, in this case, there is no variation in the expression of the G6PD gene between the maternal and paternal X chromosomes, and any observed differences in G6PD activity cannot be attributed to random X-chromosome inactivation, as both X chromosomes are carrying the same allele of the gene.

Step by step solution

01

Understanding the Lyon Hypothesis

The Lyon hypothesis, also known as X-chromosome inactivation, states that in females, one of the two X chromosomes in each cell is inactivated randomly to achieve a balance in the expression of X-linked genes between males and females. This inactivation occurs early in embryonic development and is passed on to the daughter cells during cell division. As a result, females are a mosaic of cells expressing genes from either their maternal or paternal X chromosome.
02

Understanding X-linked Inheritance

X-linked inheritance refers to genetic traits that are determined by a gene on the X chromosome. Males have only one X chromosome (inherited from their mother), while females have two X chromosomes (one inherited from each parent). This means that if a genetic trait is X-linked, males will express it more frequently, as they have only one copy of the gene, while females require two copies of the gene to express the recessive trait.
03

Knowing the G6PD Gene

The G6PD (glucose-6-phosphate dehydrogenase) gene is located on the X chromosome and is responsible for the production of an enzyme that helps protect red blood cells from damage. A mutation in this gene can lead to G6PD deficiency, which may cause a person to develop a variety of symptoms ranging from mild to severe.
04

Homozygous Female for the G6PD Gene

A human female who is homozygous for one allele of the X-linked G6PD gene has two identical copies of that allele on both her X chromosomes. This means that the gene's expression is the same in both X chromosomes and does not contribute to mosaicism due to X-chromosome inactivation.
05

Testing the Lyon Hypothesis

In this particular case, when a female is homozygous for one allele of the G6PD gene, testing the Lyon hypothesis is not feasible. This is because there is no variation in the expression of the G6PD gene between her maternal and paternal X chromosomes. Thus, any observed differences in G6PD activity cannot be attributed to random X-chromosome inactivation, as both X chromosomes are carrying the same allele of the gene.

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Most popular questions from this chapter

Under what circumstances can a male cat exhibit a tortoiseshell coat pattern?

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

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?

As related to sex determination, what is meant by (a) homomorphic and heteromorphic chromosomes; and (b) isogamous and heterogamous organisms?

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.
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