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
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Santhi’s Story http://www.ibnlive.com/videos/
28851/how-are-athletesgender-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.
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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.
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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.
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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.
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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
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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.
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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).
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(picture of chromosomes in a cell)
Human Karyotype
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
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CQ2: A karyotype was performed on an athlete. Here are the results:
From these results, the athlete is:
A: Male B: Female
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CQ3: So if Santhi is a normal female, her karyotype would be:
A: XX
B: XY
C: YY
D: XXY
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SEX
(
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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?
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Mom
Egg
46 chromosomes
(2n = diploid)
Dad
23 chromosomes Sperm
(1n = haploid)
Zygote
(fusion)
46 chromosomes again!
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Haploid and Diploid Chromosomes
Haploid with one chromatid Haploid with two chromatids
Diploid with one chromatid Diploid with two chromatids
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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.
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• 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 ).
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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.html
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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.
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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.
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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
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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.
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• 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 Xbearing and half are Y-bearing.
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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?
egg
X
X
X sperm
Y
XX
XX
XY
XY girls boys
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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.
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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.
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• Crossing over can occur anywhere along the autosomes.
• In males, the sex chromosomes (X and Y chromosomes) normally cross over only at their tips.
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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.
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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.
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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.
X
Y
SRY gene
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• 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!
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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.
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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.
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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.
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