Sex testing

The governing bodies of all-female sports sometimes use sex tests to make sure participants in their sports are female. The first attempts at gender verification were by the International Amateur Athletic Federation, whose sex test included parading naked female athletes before a panel of male doctors. In 1968 this rather dubious procedure was dropped, and the International Olympic Committee adopted the Barr test. This test uses the presence of stainable particles called Barr bodies as sex indicators. Barr bodies occur in epithelial cells in the mouth (buccal epithelial cells), and are thought to be derived from inactive X chromosomes. Females therefore usually have one Barr body in their buccal epithelial cells and males usually have none. At the 1992 Barcelona Olympics, the Barr test was replaced by the polymerase reaction test. In this test, the polymerase chain reaction. Sex testing is complicated by the fact that, on rare occasions, sex chromosomes fail to segregate at meiosis. This phenomenon, known as non-disjunction, can result in a sperm cell either having both an X and a Y chromosome or having no sex chromosome, and an egg cell either having two X chromosomes or having no sex chromosome. Non-disjunction can lead to unusual genotypes. Sex testing is confused even further by the occurrence of chimaeras. A chimaera is any animal or plant consisting of some cells with one genetic constitution and some with another. Very rarely, chimaera formation can occur during the early stages of embryonic development when chromosomes in mitotically dividing cells fail to segregate properly (for example, some cells can have the genotype XXX, others XO, while the majority are XX!).

Quick check:

1. Why are males called the heterogametic sex?

2. Explain why an embryo with an XY genotyper may develop female sexual organs.

3. Explain why a person may have buccal epithelial cells with two Barr bodies.

Discuss the role of the sex related Y gene in determining sex.

4. Describe how non-disjunction can affect the distribution of sex chromosomes in gametes and offspring.

5. Explain how sex is determined in humans.

6. Divide the text into an introduction, principal part and conclusion.

7. Express the main idea of each part.

8. Give a title to each paragraph of the text.

9. Summarize the text in brief.

Date: 2016-02-19; view: 477; Нарушение авторских прав