Transcript 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
1
Gender Testing in Sports
• Do a quick internet search to find out more
information about the history of female
gender testing in athletics.
2
Santhi’s Story
http://www.ibnlive.com/videos/2
8851/how-are-athletes-gendertested.html
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?
• Identify at least 5 characteristics to
distinguish males from females in your
small group.
5
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.
6
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
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).
9
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
10
Q2: A karyotype was performed on an athlete.
Here are the results:
From these results, the athlete is:
A: Male
B: Female
11
Q3: So if Santhi is a normal
female, her karyotype would
be:
A: XX
B: XY
C: YY
D: XXY
12
SEX
(Do I have your attention now?)
13
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?
14
SEX
Mom
46 chromosomes
(2n = diploid)
Dad
Egg
23 chromosomes
(1n = haploid)
Sperm
Zygote
(fusion)
46 chromosomes again!
15
Haploid and Diploid Chromosomes
Haploid with one chromatid
Diploid with one chromatid
Haploid with two chromatids
Diploid with two chromatids
16
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.
17
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).
18
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
19
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.
20
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.
21
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
22
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.
23
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.
24
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
25
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.
26
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.
27
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.
28
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.
29
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.
30
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
31
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!
32
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.
33
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.
34
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.
35
Review
• Use the following link to review the process of
gender testing in athletes
Gender Testing of Female Athletes
36