Transcript Cross-dressing or Crossing-over: Sex Testing of Women Athletes

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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Modified by Penny Dunning, EHS
Santhi’s Story
http://www.ibnlive.com/videos/
28851/how-are-athletesgender-tested.html
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Santhi’s Story
Santhi
Soundararajan won
the silver medal in
the 800-meter
race at the 2006
Asian Games in
Doha, Qatar.
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Santhi’s Story
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.
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18 Dec. 2006: “Indian athlete Santhi
Soundararajan fails gender test”
• 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.
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18 Dec. 2006: “Indian athlete Santhi
Soundararajan fails 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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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:
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,
– Males have one X and one Y
chromosome.
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Is there another way that sex
is characterized in humans?
• How do you visualize
chromosomes?
– Chromosomes are only visible
when preparing for nuclear
division.
– Chromosomes must be stained.
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Karyotype
(picture of chromosomes in a cell)
Human Karyotype
In diploid organisms, chromosomes
come in pairs . How many?
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CQ2: A karyotype was performed
on a different athlete. Here are
the results:
From these results, the athlete is:
A: Male
B: Female
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CQ2: A karyotype was performed
on an athlete. Here are the
results:
From these results, the athlete is:
Male
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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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CQ3: So if Santhi is a
normal female, her
karyotype would be:
A: XX
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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
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.
Are the following statements
TRUE or FALSE?
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A. These chromatids make up a
diploid chromosome.
False
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B. The cell that contains these
sister chromatids must be
diploid.
False
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C. The sister chromatids were
formed by replicating a single
chromatid.
True
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D. The sister chromatids were joined
by fertilization, bringing together a
maternal and paternal chromatid.
False
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Meiosis
• Purpose of meiosis:
– in animals, to produce gametes with
just half the parents’ genetic
material.
Gametes are _____(haploid/diploid).
Haploid
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Meiosis
• 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: Which one 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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CQ5: Which one is true after
Meiosis I?
B: The cells are haploid.
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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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CQ6: During Meiosis II:
D: Sister chromatids separate.
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Sources of Genetic Variability in
Meiosis
Independent
Assortment
• Each pair of
homologous
chromosomes
lines up at
Metaphase I
plate.
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Sources of Genetic Variability in
Meiosis
Independent
Assortment
• There is a
50:50 chance
that a daughter
cell will get one
or the other
copy of the
chromosome.
Animation:
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http://wps.prenhall.com/wps/media/objects/487/498795/CDA10_2/CDA10_2b/CDA10_2b.htm
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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CQ7: How many possible
combinations of maternal
chromosomes are possible in a
human ovum due to independent
assortment during meiosis?
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 Ybearing.
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Sex Determination
• In mammals, males have one X and
one Y chromosome.
• A special cell division called
Meiosis will form gametes (sperm)
• Half their sperm are X-bearing
and half are Y-bearing.
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Sex Determination
• In mammals, females have two X
chromosomes.
• A special cell division called
Meiosis will form gametes (eggs)
• All eggs are are X-bearing.
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How is Sex Determined in Humans?
• Sex is determined
by the sex
chromosome
carried by the
sperm.
• What percent of
offspring will be
boys and what
percent will be
girls?
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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CQ8: Could Santhi
have an XX karyotype
and be male?
We will see…
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Sources of Genetic Variability
in Meiosis
Crossing Over During Meiosis
• When homologous
chromosomes pair
during meiosis,
non-sister
chromatids
exchange
homologous
portions.
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Sources of Genetic Variability
in Meiosis
Crossing Over During Meiosis
• A chiasma forms
between the nonsister chromatids
at the point of
crossing over.
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Sources of Genetic Variability
in Meiosis
Crossing Over During Meiosis
• 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 if at all.
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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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CQ9: During crossover, all of the
following happen EXCEPT:
C: Crossing over decreases the
genetic variability in the gametes.
(Crossing over actually INCREASES
the genetic variability in the
gamets)
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How is Sex Characterized in
Humans?
• Anatomy –What they look like,
genitals
• Physiology – hormones
• Chromosomes- XX or XY
• But there is a 4th answer:
Genes
Specific genes determine whether an
embryo will develop as a male or
female.
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SRY Gene
(Sex-Determining Region of the
Y chromosome)
SRY
gene
• Early in development,
the immature gonads
of males and females
are indistinguishable.
Y
X
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SRY Gene
(Sex-Determining Region of the
Y chromosome)
• 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.
SRY
gene
Y
X
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SRY Gene
(Sex-Determining Region of the
Y chromosome)
SRY
gene
• 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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Can you have an XX male or XY
female?
•
•
•
•
What sex is
What sex is
What sex is
What sex is
XX (SRY-)?
XY (SRY+)?
XX (SRY+)?
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 (according to
her chromosomes, but not SRY
gene) 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?
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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.
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What about Santhi
Soundararajan?
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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