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Transcript
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 Penny Dunning, EHS
Santhi’s Story
http://www.ibnlive.com/videos/
28851/how-are-athletesgender-tested.html
2
Santhi’s Story
Santhi
Soundararajan won
the silver medal in
the 800-meter
race at the 2006
Asian Games in
Doha, Qatar.
3
Santhi’s Story
Following her silver
medal
performance, her
sex was officially
questioned.
4
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.
5
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.
6
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.
7
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.
8
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.
9
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
10
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
11
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.
12
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.
13
Karyotype
(picture of chromosomes in a cell)
Human Karyotype
In diploid organisms, chromosomes
come in pairs . How many?
15
CQ2: A karyotype was performed
on a different athlete. Here are
the results:
From these results, the athlete is:
A: Male
B: Female
17
CQ2: A karyotype was performed
on an athlete. Here are the
results:
From these results, the athlete is:
Male
18
CQ3: So if Santhi is a
normal female, her
karyotype would be:
A: XX
B: XY
C: YY
D: XXY
19
CQ3: So if Santhi is a
normal female, her
karyotype would be:
A: XX
20
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?
22
SEX
Mom
46 chromosomes
(2n = diploid)
Dad
Egg
23 chromosomes
(1n = haploid)
Sperm
Zygote
(fusion)
46 chromosomes again!
23
Haploid and Diploid Chromosomes
Haploid with one chromatid
Haploid with two chromatids
24
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?
25
A. These chromatids make up a
diploid chromosome.
False
26
B. The cell that contains these
sister chromatids must be
diploid.
False
27
C. The sister chromatids were
formed by replicating a single
chromatid.
True
28
D. The sister chromatids were joined
by fertilization, bringing together a
maternal and paternal chromatid.
False
29
Meiosis
• Purpose of meiosis:
– in animals, to produce gametes with
just half the parents’ genetic
material.
Gametes are _____(haploid/diploid).
Haploid
30
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).
31
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
32
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.
33
CQ5: Which one is true after
Meiosis I?
B: The cells are haploid.
34
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.
35
CQ6: During Meiosis II:
D: Sister chromatids separate.
36
Sources of Genetic Variability in
Meiosis
Independent
Assortment
• Each pair of
homologous
chromosomes
lines up at
Metaphase I
plate.
37
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:
38
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.
39
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.
40
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.
41
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.
42
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.
43
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
44
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.
46
CQ8: Could Santhi
have an XX karyotype
and be male?
We will see…
47
Sources of Genetic Variability
in Meiosis
Crossing Over During Meiosis
• When homologous
chromosomes pair
during meiosis,
non-sister
chromatids
exchange
homologous
portions.
48
Sources of Genetic Variability
in Meiosis
Crossing Over During Meiosis
• A chiasma forms
between the nonsister chromatids
at the point of
crossing over.
49
Sources of Genetic Variability
in Meiosis
Crossing Over During Meiosis
• Following crossing
over, the
chromatids are
recombinant,
combining paternal
and maternal
genes.
50
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.
51
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.
52
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)
53
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.
54
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
55
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
56
SRY Gene
(Sex-Determining Region of the
Y chromosome)
SRY
gene
• Females: With no SRY
gene, gonads develop as
ovaries by default.
Y
X
57
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!
58
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!
59
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.
60
CQ11: What do you think
about requiring gender
testing for female athletes
in international
competition?
61
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.
62
What about Santhi
Soundararajan?
Santhi was stripped of
her silver medal.
63
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.
64