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Chapter 7: Problem 23

What does the apparent need for dosage compensation mechanisms suggest about the expression of genetic information in normal diploid individuals?

Short Answer

Expert verified
Provide an example of a dosage compensation mechanism. Answer: Dosage compensation mechanisms are systems that equalize gene expression levels between different sexes or chromosomes in organisms. These mechanisms are crucial for diploid individuals to maintain a balanced expression of genetic information, preventing the development of abnormal traits or health issues. One example of a dosage compensation mechanism is X-inactivation in mammals, where one X chromosome in females is randomly inactivated to prevent overexpression of X-linked genes.

Step by step solution

01

Defining dosage compensation mechanisms

Dosage compensation mechanisms are systems that organisms have evolved to equalize the expression of genes between members of different sexes or to balance the expression of genes from different chromosomes. In multicellular organisms with sexual reproduction, each sex typically has a specific combination of sex chromosomes: for example, in humans, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). Dosage compensation mechanisms ensure that gene expression levels are equalized between the sexes, even though they have different numbers of certain genes.
02

The need for dosage compensation in diploid individuals

In diploid individuals, each cell contains two copies of every gene, one from each parent. The expression of these genes determines the individual's traits and characteristics. If there isn't a balance in the expression of genes between the two copies, the individual could develop abnormal traits or health issues. This is why dosage compensation mechanisms are crucial in diploid organisms like humans.
03

Example of dosage compensation: X inactivation in mammals

In mammals, one of the most well-known dosage compensation mechanisms is X-inactivation, which occurs in females. Since females have two X chromosomes, one of the X chromosomes is randomly inactivated (also called "silencing") in each cell, resulting in only one functional X chromosome. This prevents an overexpression of genes on the X chromosome, which could lead to undesirable phenotypic effects and health issues.
04

Implications of the need for dosage compensation

The apparent need for dosage compensation mechanisms suggests that maintaining proper levels of gene expression is crucial for the normal functioning of diploid individuals. It highlights the importance of a delicate balance in the expression of genetic information, ensuring that organisms develop and function correctly. If dosage compensation mechanisms were absent or ineffective, there could be serious consequences for the health and development of the affected individuals due to imbalances in gene expression.

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Most popular questions from this chapter

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

Distinguish between the terms homomorphic and heteromorphic chromosomes, and between isogamous and heterogamous organisms.

When cows have twin calves of unlike sex (fraternal twins), the female twin is usually sterile and has masculinized reproductive organs. This calf is referred to as a freemartin. In cows, twins may share a common placenta and thus fetal circulation. Predict why a freemartin develops.

Indicate the expected number of Barr bodies in interphase cells of individuals with Klinefelter syndrome; Turner syndrome; and karyotypes \(47, \mathrm{XYY}, 47, \mathrm{XXX},\) and \(48, \mathrm{XXXX}\)

In a number of organisms, including Drosophila and butterflies, genes that alter the sex ratio have been described. In the pest species Musca domesticus (the house fly), Aedes aegypti (the mosquito that is the vector for yellow fever), and Culex pipiens (the mosquito vector for filariasis and some viral dis- eases), scientists are especially interested in such genes. Sex in Culex is determined by a single gene pair, \(M m\) being male and \(m m\) being female. Males homozygous for the recessive gene \(d d\) never produce many female offspring. The \(d d\) combination in males causes fragmentation of the \(m\) -bearing dyad during the first meiotic division, hence its failure to complete spermatogenesis. (a) Account for this sex-ratio distortion by drawing labeled chromosome arrangements in primary and secondary spermatocytes for each of the following genotypes: \(M m D d\) and \(M m d d .\) How do meiotic products differ between \(D d\) and \(d d\) genotypes? Note that the diploid chromosome number is 6 in Culex pipiens and both \(D\) and \(M\) loci are linked on the same chromosome. (b) How might a sex-ratio distorter such as \(d d\) be used to control pest population numbers?
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