Presentation on theme: "1 Cross-Dressing or Crossing-Over: Sex Testing of Women Athletes Maureen Knabb, Department of Biology, West Chester University, and Joan Sharp, Biological."— Presentation transcript:
1 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
2 Santhi’s Story http://www.ibnlive.com/videos/ 28851/how-are-athletes- gender-tested.html Santhi Soundararajan won the silver medal in the 800-meter race at the 2006 Asian Games in Doha, Qatar. Following her silver medal performance, her sex was officially questioned.
3 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. 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. 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.
4 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.
5 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.
6 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
7 Is there another way that sex is characterized in humans? Chromosomes: –Females possess two X chromosomes in each of their cells, whereas males have one X and one Y chromosome. How do you visualize chromosomes? –Chromosomes are only visible when preparing for nuclear division. –Chromosomes must be stained.
8 What does an individual chromosome look like? During nuclear division, DNA is tightly packed. This chromosome is composed of 2 chromatids. In this diagram, the DNA has replicated (more on this later).
9 Karyotype (picture of chromosomes in a cell) In diploid organisms, chromosomes come in pairs (e.g., 23 pairs for humans). How do you make a karyotype? http://learn.genetics.utah.edu/units/disorders/karyotype/karyotype.cfm Human Karyotype
10 CQ2: A karyotype was performed on an athlete. Here are the results: From these results, the athlete is: A: Male B: Female
11 CQ3: So if Santhi is a normal female, her karyotype would be: A: XX B: XY C: YY D: XXY
15 Haploid and Diploid Chromosomes Haploid with two chromatidsHaploid with one chromatid Diploid with one chromatidDiploid with two chromatids
16 CQ4: Assume that this is one of Santhi’s chromosomes. This chromosome is composed of two chromatids joined by a centromere. A: These chromatids make up a diploid chromosome. B: The cell that contains these sister chromatids must be diploid. C: The sister chromatids were formed by replicating a single chromatid. D: The sister chromatids were joined by fertilization, bringing together a maternal and paternal chromatid.
17 Meiosis Purpose of meiosis: in animals, produce gametes with just half the parents’ genetic material. Gametes are ______ (haploid/diploid). Mechanism: Only one of each pair of homologous chromosomes gets into each gamete. The happy ending: Gametes from the two parents get to fuse, restoring the original number of chromosomes in the fertilized egg (zygote).
18 Stages of Meiosis Meiosis (in animals) produces 4 haploid cells from 1 diploid cell. At the end of the first division (Meiosis I) the 2 cells are already haploid. The second division (Meiosis II) splits the 2 sister (identical, replicated DNA) chromatids to 1 chromatid. Animation: http://www.johnkyrk.com/meiosis.htmlhttp://www.johnkyrk.com/meiosis.html
19 CQ5: What is true after Meiosis I? A: Four cells have been produced. B: The cells are haploid. C: The DNA will be replicated once more. D: The cells are ready to perform as gametes. E: Each chromosome consists of a single strand of DNA.
20 CQ6: During Meiosis II: A: Homologous chromosomes separate. B: The DNA is replicated. C: Gametes fuse. D: Sister chromatids separate. E: All of the above.
21 Sources of Genetic Variability in Meiosis Independent Assortment Each pair of homologous chromosomes lines up at Metaphase I plate. There is a 50:50 chance that a daughter cell will get one or the other copy of the chromosome. Animation: http://wps.prenhall.com/wps/media/objects/487/498795/CDA10_2/CDA10_2b/CDA10_2b.htm http://wps.prenhall.com/wps/media/objects/487/498795/CDA10_2/CDA10_2b/CDA10_2b.htm
22 CQ7: How many possible combinations of maternal chromosomes are possible in a human ovum due to independent assortment during meiosis? A: 23 combinations. B: 46 combinations. C: 23 2 = 529 combinations. D: 2 23 = ~ 8 million combinations.
23 Sex Determination In mammals, males have one X and one Y chromosome. In males, half the daughter cells formed by Meiosis I get an X chromosome and half get a Y chromosome. Following Meiosis II and sperm differentiation, half the sperm are X- bearing and half are Y-bearing.
24 How is Sex Determined in Humans? Sex is determined by the sex chromosome carried by the sperm. What sex chromosome is carried by the egg? sperm egg XXXY XXXY girlsboys X X Y X
25 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.
26 Sources of Genetic Variability in Meiosis Crossing Over During Meiosis When homologous chromosomes pair during Prophase I, non-sister chromatids exchange homologous portions. A chiasma forms between the non-sister chromatids at the point of crossing over. Following crossing over, the chromatids are recombinant, combining paternal and maternal genes.
27 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.
28 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.
29 How is Sex Characterized in Humans? In addition to anatomy, physiology, and chromosomes, there is a 4 th answer: Genes: Specific genes determine whether an embryo will develop as a male or female.
30 SRY (Sex- Determining Region of the Y chromosome) Gene Early in development, the immature gonads of males and females are indistinguishable. Males: In the 7 th week of development, the SRY gene on the Y chromosome activates a number of genes, and the gonads develop as testes. Females: With no SRY gene, gonads develop as ovaries by default. SRY gene X Y
31 Can you have an XX male or XY female? Watch this video: http://www.hhmi.org/biointeractive/media/meiosis-lg.mov 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!
32 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 male, take her medal away. C: Perform additional tests.
33 CQ11: What do you think about requiring gender testing for female athletes in international competition? 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.
34 What about Santhi Soundararajan? Santhi was stripped of her silver medal. An anonymous official in the know has reported that Ms. Soundarajan's tests revealed more Y chromosomes than are usually present in the genetic make-up of a female. No official statement has been made.