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Cross-Dressing or Crossing-Over: Sex Testing of Women Athletes Maureen Knabb, Department of Biology, West Chester University, and Joan Sharp, Biological Sciences, Simon Fraser University 1 Modified by Penny Dunning, EHS Santhi’s Story Santhi Soundararajan won the silver medal in the 800-meter race at the 2006 Asian Games in Doha, Qatar. 3 Santhi’s Story Following her silver medal performance, her sex was officially questioned. 4 18 Dec. 2006: “Indian athlete Santhi Soundararajan fails gender test” • Top Indian woman athlete Santhi Soundararajan, who won a silver medal at a recent regional championship, has failed a gender test, according to official reports. 5 18 Dec. 2006: “Indian athlete Santhi Soundararajan fails gender test” • Sports writer KP Mohan said that a team of doctors, including a gynecologist, endocrinologist and psychologist, normally examines athletes and puts them through physical and clinical examinations during a gender test. 6 18 Dec. 2006: “Indian athlete Santhi Soundararajan fails gender test” • Santhi Soundararajan's test was done soon after Soundararajan came in second in the women's 800m race on 9 December, but it is not clear how she failed the test at the Asian Games in Doha. 7 How do you know if someone is male or female? • Talk to the person next to you and identify at least 5 characteristics to distinguish males from females. 8 How is sex determined in humans? • Anatomy: Primary and secondary sexual characteristics - genitalia, body hair, pelvis, etc. • Physiology: Function and interaction of the sex organs including concentrations of sex hormones such as estrogen, progesterone, and testosterone. 9 CQ1: Imagine you are a member of the committee assigned to determine whether Santhi is female. Here are possible results of the initial tests (we don’t know the real results): Female genitalia: Yes Breasts and pubic hair: Yes Regular menstrual cycle: Never From this information, you conclude that Santhi is: A: Male B: Female 10 CQ1: Imagine you are a member of the committee assigned to determine whether Santhi is female. Here are possible results of the initial tests (we don’t know the real results): Female genitalia: Yes Breasts and pubic hair: Yes Regular menstrual cycle: Never From this information, you conclude that Santhi is: B: Female 11 Is there another way that sex is characterized in humans? • Chromosomes: – Females possess two X chromosomes in each of their cells, – Males have one X and one Y chromosome. 12 Is there another way that sex is characterized in humans? • How do you visualize chromosomes? – Chromosomes are only visible when preparing for nuclear division. – Chromosomes must be stained. 13 Karyotype (picture of chromosomes in a cell) Human Karyotype In diploid organisms, chromosomes come in pairs . How many? 15 CQ2: A karyotype was performed on a different athlete. Here are the results: From these results, the athlete is: A: Male B: Female 17 CQ2: A karyotype was performed on an athlete. Here are the results: From these results, the athlete is: Male 18 CQ3: So if Santhi is a normal female, her karyotype would be: A: XX B: XY C: YY D: XXY 19 CQ3: So if Santhi is a normal female, her karyotype would be: A: XX 20 The Fate of Genetic Material During Sexual Reproduction • You contain genetic material from both your Mom and Dad. • You have 46 chromosomes, and so do (will) your children. • How does this happen? 22 SEX Mom 46 chromosomes (2n = diploid) Dad Egg 23 chromosomes (1n = haploid) Sperm Zygote (fusion) 46 chromosomes again! 23 Sex Determination • In mammals, males have one X and one Y chromosome. • A special cell division called Meiosis will form gametes (sperm) • Half their sperm are X-bearing and half are Y-bearing. 42 Sex Determination • In mammals, females have two X chromosomes. • A special cell division called Meiosis will form gametes (eggs) • All eggs are are X-bearing. 43 How is Sex Determined in Humans? • Sex is determined by the sex chromosome carried by the sperm. • What percent of offspring will be boys and what percent will be girls? sperm X X Y XX XY XX XY girls boys egg X 44 CQ8: Could Santhi have an XX karyotype and be male? A: No, an XX individual is always female. B: Yes, this is common. C: Yes, if a male-determining control gene is carried on one of her X chromosomes. 46 CQ8: Could Santhi have an XX karyotype and be male? We will see… 47 Sources of Genetic Variability in Meiosis Crossing Over During Meiosis • When homologous chromosomes pair during meiosis, non-sister chromatids exchange homologous portions. 48 Sources of Genetic Variability in Meiosis Crossing Over During Meiosis • A chiasma forms between the nonsister chromatids at the point of crossing over. 49 Sources of Genetic Variability in Meiosis Crossing Over During Meiosis • Following crossing over, the chromatids are recombinant, combining paternal and maternal genes. 50 Crossing Over • Crossing over can occur anywhere along the autosomes. • In males, the sex chromosomes (X and Y chromosomes) normally cross over only at their tips if at all. 51 CQ9: During crossover, all of the following happen EXCEPT: A: The homologous chromosomes line up in pairs. B: The homologous chromosomes swap pieces with their adjacent partners. C: Crossing over decreases the genetic variability in the gametes. D: Each chromatid is unique after it has crossed over. 52 CQ9: During crossover, all of the following happen EXCEPT: C: Crossing over decreases the genetic variability in the gametes. (Crossing over actually INCREASES the genetic variability in the gamets) 53 How is Sex Characterized in Humans? • Anatomy –What they look like, genitals • Physiology – hormones • Chromosomes- XX or XY • But there is a 4th answer: Genes Specific genes determine whether an embryo will develop as a male or female. 54 SRY Gene (Sex-Determining Region of the Y chromosome) SRY gene • Early in development, the immature gonads of males and females are indistinguishable. Y X 55 SRY Gene (Sex-Determining Region of the Y chromosome) • Males: In the 7th week of development, the SRY gene on the Y chromosome activates a number of genes, and the gonads develop as testes. SRY gene Y X 56 SRY Gene (Sex-Determining Region of the Y chromosome) SRY gene • Females: With no SRY gene, gonads develop as ovaries by default. Y X 57 Can you have an XX male or XY female? • Watch this video: http://www.hhmi.org/biointeractive/media/meiosis-lg.mov • What sex is XX (SRY+)? • What sex is XY (SRY-)? Sex reversal occurs in 1 in 20,000 births! 58 CQ10: If you were a member of the Asian Games medal committee and Santhi’s karyotype revealed that she is XY and SRY-, what would you do? A: She has female genitalia, allow her to keep her medal. B: She is genetically (according to her chromosomes, but not SRY gene) male, take her medal away. C: Perform additional tests. 59 CQ11: What do you think about requiring gender testing for female athletes in international competition? 60 A: It should be banned because gender determination is so complex. B: It is necessary to ensure an even playing field. C: It is necessary, but needs to include a large number of genetic tests to ensure fairness. D: It should be required for all athletes, both male and female. 61 What about Santhi Soundararajan? Santhi was stripped of her silver medal. 62