Download Cross-dressing or Crossing-over: Sex Testing of Women

Cross-Dressing or Crossing-Over: Sex
Testing of Women Athletes
Modified from: Maureen Knabb, Department of Biology, West Chester
University, and Joan Sharp, Biological Sciences, Simon Fraser University
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Gender Testing in Sports
• Do a quick internet search to find out more
information about the history of female
gender testing in athletics.
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Santhi’s Story
http://www.ibnlive.com/videos/2
8851/how-are-athletes-gendertested.html
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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?
• Identify at least 5 characteristics to
distinguish males from females in your
small group.
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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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Q1: 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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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
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Q2: 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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Q3: 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?
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SEX
Mom
46 chromosomes
(2n = diploid)
Dad
Egg
23 chromosomes
(1n = haploid)
Sperm
Zygote
(fusion)
46 chromosomes again!
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Haploid and Diploid Chromosomes
Haploid with one chromatid
Diploid with one chromatid
Haploid with two chromatids
Diploid with two chromatids
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Q4: 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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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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Q5: 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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Q6: 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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Q7: 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?
•
•
Sex is determined by
the sex chromosome
carried by the sperm.
sperm
X
What sex chromosome egg
is carried by the egg?
X
X
Y
XX
XY
XX
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
• 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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Q9: 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
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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!
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Q10: 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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Q11: 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.
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Review
• Use the following link to review the process of
gender testing in athletes
Gender Testing of Female Athletes
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