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
1
Modified by Liz Murray for IST 341
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.
2
Caster Semenya
• Caster Semenya,
18, the world
champion 800meter runner in
2009
• muscular, huskyvoiced, extremely
fast
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.
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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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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
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.
8
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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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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CSo 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
Haploid with two chromatids
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Diploid with one chromatid
Diploid with two chromatids
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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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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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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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 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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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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Recombination generates variation
• Crossing-over is:
– The physical exchange of chromosomal
material between chromatids of homologous
chromosomes.
• Result: Generation of new combinations
of genes (alleles) if the genes are located
on the same chromosome.
Recombination (crossing over)
A
A
• Occurs in prophase of
meiosis I
• Generates diversity
• Group of genes on
one chromosome are
called the haplotype.
B
B
C
b
C
D D
E
F
E
F
a
a
b
c
c
d
d
e
f
Recombination creates chromosomes with new
combinations of alleles for genes A to F.
e
f
Recombination
• Occurs in prophase of
meiosis I
A
a
B
b
C
C
c
c
• Generates diversity
Letters denote genes
Case denotes alleles
D D
E
F
d
E
F
e
f
Recombination creates chromosomes with new
combinations of alleles for genes A to F.
d
e
f
Recombination (crossing over)
• Occurs in prophase of
meiosis I
a
A
B
b
C
A
a
B
b
C
c
c
d
d
• Generates diversity
D
Letters denote genes
Case denotes alleles
E
F
D
E
F
e
f
Recombination creates chromosomes with new
combinations of alleles for genes A to F.
e
f
Recombination creates chriamata
The two sources of
genetic variation in
meiosis are independent
assortment and genetic
recombination.
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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Gametogenesis
• Spermatogenesis
• Oogenesis
Spermatogenesis
Spermatogenesis
• Stem cells in testes
divide mitotically to
create a pool of
spermocytes.
• Meiosis produces
spermatids from
spermatogonium.
• Spermiogenesis is
the process of
forming mature
sperm.
Oogenesis
First polar body
may divide
(haploid)
a
a
X
a
X
a
Meiosis I
A
Oogonium
(diploid)
X
X
Mitosis
X
Primary
oocyte
(diploid)
Polar
bodies
die
Meiosis II
(if fertilization
occurs)
A
X
A
X
Secondary
oocyte
(haploid)
Ovum (egg)
A
X
Second
polar body
(haploid)
Mature
egg
Ovum Formation
• One of four meiotic products becomes
an ovum.
• The three remaining meiotic products
are polar bodies.
Oogenesis vs spermatogenesis
Meiosis lasts much longer in
oogenesis in humans
Fertilization
• Fertilization is the joining of sperm and ovum.
• Meiosis II in the ovum is completed at the time of
fertilization forming one ovum and one polar body.
• Following fertilization, chemical reactions occur
preventing additional sperm from entering the ovum.
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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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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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 is the I.A.A.F. to do?
• Eric Vilain, a professor of human genetics
and pediatrics at U.C.L.A., specializes in
sex development, so he knows that
looking at genes will not tell you simply
how a body is functioning.
• “The best biological marker, if you want a
level playing field, would probably be
functional testosterone,” Vilain said.
“There is a good correlation between
functional testosterone and muscle mass.”50
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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What About Caster
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