CrossDressing or CrossingOver: Sex Testing of Women Athletes

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
Santhis Story

• http//www.ibnlive.com/videos/28851/how-are-athle
  tes-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.

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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 dont 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.

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What does an individual chromosome look like?
0

• 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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Karyotype(picture of chromosomes in a cell)
0
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/kar
  yotype/karyotype.cfm

10
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

12
SEX(Do I have your attention now?)
0
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The Fate of Genetic Material During Sexual
Reproduction
0

• 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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SEX

• Mom 46 chromosomes Dad
• (2n diploid)
• Egg 23 chromosomes Sperm
• (1n haploid)
• Zygote
• (fusion)
• 46 chromosomes again!

15
Haploid and Diploid Chromosomes
Haploid with two chromatids
Haploid with one chromatid
Diploid with one chromatid
Diploid with two chromatids
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CQ4 Assume that this is one of Santhis
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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Meiosis
0

• 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
0

• 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?

0

• 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

0

• 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 5050 chance that a daughter cell will
  get one or the other copy of the chromosome.

Animation http//wps.prenhall.com/wps/media/objec
ts/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 232 529 combinations.
• D 223 8 million combinations.

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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.

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How is Sex Determined in Humans?
sperm

• Sex is determined by the sex chromosome carried
  by the sperm.
• What sex chromosome is carried by the egg?

X
Y
X
XX
XY
egg
XX
XY
X
girls
boys
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.

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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

• 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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How is Sex Characterized in Humans?

• In addition to anatomy, physiology, and
  chromosomes, there is a 4th 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 7th 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
Y
X
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Can you have an XX male or XY female?

• Watch this video http//www.hhmi.org/biointeracti
  ve/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 Santhis 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.

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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.