Chapter 12, Problem 7CTE

A man is homozygous dominant for ten different genes that assort independently. How many genotypically different types of sperm could he produce? A woman is homozygous recessive for eight of these genes and is heterozygous for the other two. How many genotypically different types of eggs could she produce? What can you conclude about the relationship between the number of different gametes possible and the number of heterozygous and homozygous gene pairs that are present?

As outlined in this chapter, sex can be defined at several levels: chromosomal, gonadal, and phenotypic. To this we can add psychological sex, the sex one believes themselves to be. Determining someones sex is a complex issue that is often difficult to resolve, as the case of Bruce Reimer (see Section 7.1) illustrates. In spite of the complexity surrounding this issue, the International Olympic Committee (IOC) and the International Association of Athletics Federations (IAFF) still use sex testing on female athletes to determine whether they can compete in athletic events as females. This has led to serious personal, social, and legal issues, and the practice has been widely condemned and widely defended. Lets examine two such cases here. An Indian athlete, Santhi Soundarajan, finished second in the 800-meter run at the Asian Games in Doha, Qatar, in 2006. After the race, she was asked to take a sex test. According to press reports, the tests showed that she appeared to have abnormal chromosomes. An official stated that she had more Y chromosomes than allowed. As a result, she was stripped of her medal, banned from further competition by the Indian Olympic Association, and shunned by her local community. Before the race in Doha, Santhi had competed in 8 international competitions and won 12 medals. Sometime after this incident, she attempted suicide. She now runs a training school for athletes in Tamil Nadu, India. Although the number and types of tests done on Santhi have not been revealed, such tests usually involve examination of the external genitals, a chromosome analysis, and measurement of hormone levels. Suppose you were on the committee deciding whether Santhi could compete as a female. Consider each of the following hypothetical tests one at a time and base your conclusions only on the results of that test. The results of a physical examination show she has female genitals. On this basis, would you allow her to keep her medal and compete as a female in future races? Suppose the results of a chromosomal analysis shows that she has an XY chromosome set and is chromosomally male. Would you allow her to keep her medal and compete as a female? Lastly, suppose a test for hormone levels shows that she has levels of the male sex hormone testosterone that are higher than average for females but at least 10 times lower than the average for males. Would you allow her to keep her medal and compete in future races as a female? Now, put the results of all three tests together, and consider them as a whole. What are your conclusions? Now, lets consider the case of a South African runner, Caster Semenya, who won the 800-meter run at the World Championships held in Berlin, Germany, in 2009. After the race, she was asked to undergo sex testing. The IAAF stated that the tests were requested to ascertain whether she had a rare medical condition that gave her an unfair physical advantage. The nature of the tests and their results were not released, but press reports indicate that she did not have ovaries or a uterus, and had testosterone levels intermediate between the averages for males and females. In the end, the IAAF agreed to keep the results of her tests confidential, and Caster was allowed to keep her medal and return to international competition in 2010. In both cases, what the IAAF considers the threshold for determining who can compete as a female has not been stated. Would you recommend that testing of female athletes be continued to ensure that males do not compete as females? Or should all such testing be banned?

Because of the ________ alignment of homologous chromosomes during meiosis, gametes can end up with _________ mixes of maternal and paternal chromosomes. a. unvarying; different b. unvarying; duplicate c. random; duplicate d. random; different

Which of the following statements is not true in comparing mitosis and meiosis? a. Twice the number of cells are produced in meiosis as in mitosis. b. Meiosis is involved in the production of gametes, unlike mitosis. c. Crossing over occurs in meiosis I but not in meiosis II or mitosis. d. Meiosis and mitosis both produce cells that are genetically identical. e. In both mitosis and meiosis, the parental cell is diploid.

As outlined in this chapter, sex can be defined at several levels: chromosomal, gonadal, and phenotypic. To this we can add psychological sex, the sex one believes themselves to be. Determining someones sex is a complex issue that is often difficult to resolve, as the case of Bruce Reimer (see Section 7.1) illustrates. In spite of the complexity surrounding this issue, the International Olympic Committee (IOC) and the International Association of Athletics Federations (IAFF) still use sex testing on female athletes to determine whether they can compete in athletic events as females. This has led to serious personal, social, and legal issues, and the practice has been widely condemned and widely defended. Lets examine two such cases here. An Indian athlete, Santhi Soundarajan, finished second in the 800-meter run at the Asian Games in Doha, Qatar, in 2006. After the race, she was asked to take a sex test. According to press reports, the tests showed that she appeared to have abnormal chromosomes. An official stated that she had more Y chromosomes than allowed. As a result, she was stripped of her medal, banned from further competition by the Indian Olympic Association, and shunned by her local community. Before the race in Doha, Santhi had competed in 8 international competitions and won 12 medals. Sometime after this incident, she attempted suicide. She now runs a training school for athletes in Tamil Nadu, India. Although the number and types of tests done on Santhi have not been revealed, such tests usually involve examination of the external genitals, a chromosome analysis, and measurement of hormone levels. Suppose you were on the committee deciding whether Santhi could compete as a female. Consider each of the following hypothetical tests one at a time and base your conclusions only on the results of that test. The results of a physical examination show she has female genitals. On this basis, would you allow her to keep her medal and compete as a female in future races? Suppose the results of a chromosomal analysis shows that she has an XY chromosome set and is chromosomally male. Would you allow her to keep her medal and compete as a female? Lastly, suppose a test for hormone levels shows that she has levels of the male sex hormone testosterone that are higher than average for females but at least 10 times lower than the average for males. Would you allow her to keep her medal and compete in future races as a female? Now, put the results of all three tests together, and consider them as a whole. What are your conclusions? Now, lets consider the case of a South African runner, Caster Semenya, who won the 800-meter run at the World Championships held in Berlin, Germany, in 2009. After the race, she was asked to undergo sex testing. The IAAF stated that the tests were requested to ascertain whether she had a rare medical condition that gave her an unfair physical advantage. The nature of the tests and their results were not released, but press reports indicate that she did not have ovaries or a uterus, and had testosterone levels intermediate between the averages for males and females. In the end, the IAAF agreed to keep the results of her tests confidential, and Caster was allowed to keep her medal and return to international competition in 2010. In both cases, what the IAAF considers the threshold for determining who can compete as a female has not been stated. Based on what is known about the test results in this case and the hypothetical tests in the first case, do you think the outcome in each case was fair?

Assume that the ratio of females to males is 1:1. A couple already has two daughters and no sons. If they plan to have a total of six children, what is the probability that they will have four more girls? (a) (b) (c) 116 (d) 132 (e) 164

Adams maternal and paternal chromosomes have alternate forms of a gene that influences whether a person is right-handed or left-handed. One form says right and its partner says left. Visualize one of Adams spermatogonia, in which chromosomes are being duplicated prior to meiosis. Visualize what happens to the chromosomes during anaphase I and II. (It might help to use toothpicks as models of the sister chromatids of each chromosome.) What fraction of Adam's sperm will carry the gene for right-handedness? For left-handedness?

In the fertility awareness method of birth control, a woman gauges her monthly fertile period by monitoring changes in the consistency of her vaginal mucus. What kind of information does such a method provide about the likelihood of getting pregnant?

Birth Defects and Multiple Births A woman who carries multiple offspring at the same time increases the risk of some birth defects. FIGURE 42.18 shows the results of Yiwei Tang's study of birth defects reported in Florida from 1W6 to 2000. Tang compared the incidence of various defects among single and multiple births. She calculated the relative risk for each type of defect based on type of birth, and corrected for other differences that might increase risk such as maternal age, income, race, and medical care during pregnancy. A relative risk of less than 1 means that multiple births pose less risk of that defect occurring. A relative risk greater than 1 means multiples are more likely to have a defect. FIGURE 42.18 Prevalence, per 10,000 live births, of various types of birth defects among multiple aria single births. Relative risk for each defect is given after researches adjusted for the motor's age, race, previous adverse pregnancy experience, education, Medicaid participation during pregnancy, as well as the infant's sex and number of siblings. 4. Does a multiple pregnancy increase the relative risk of chromosomal defects in offspring?