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
Santhi’s Story
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.
“Indian Athlete Fails Gender Test”
http://news.bbc.co.uk/2/hi/world/so
uth_asia/6188775.stm
2
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.
3
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.
4
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.
5
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
6
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.
7
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).
8
Karyotype
(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
9
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
(Do I have your attention now?)
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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?
13
SEX
Mom
46 chromosomes
(2n = diploid)
Dad
Egg
23 chromosomes
(1n = haploid)
Sperm
Zygote
(fusion)
46 chromosomes again!
14
Haploid and Diploid Chromosomes
Haploid with one chromatid
Haploid with two chromatids
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Diploid with one chromatid
Diploid with two chromatids
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.
16
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).
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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: 232 = 529 combinations.
D: 223 = ~ 8 million combinations.
22
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 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?
sperm
X
X
Y
XX
XY
XX
XY
girls
boys
egg
X
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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
• 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.
SRY
gene
• 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.
Y
X
30
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!
31
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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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.
34