Cross-Dressing or Crossing-Over:
Sex Testing of Women Athletes
Santhi’s Story
http://www.ibnlive.com/videos/
28851/how-are-athletes-gender-tested.html
Santhi Soundararajan won the silver medal in the 800-meter race at the 2006 Asian Games in Doha, Qatar.
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
How do you know if someone is
male or female?
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
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:
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.
What does an individual
chromosome look like?
• During nuclear division,
DNA is tightly packed.
• This chromosome is
composed of 2
chromatids.
Karyotype
(picture of chromosomes in a cell)
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
CQ2: A karyotype was performed on
an athlete. Here are the results:
From these results, the athlete is:
CQ3: So if Santhi is a
normal female, her
karyotype would be:
SEX
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
SEX
Mom 46 chromosomes
Dad
(2n = diploid)
Egg
23 chromosomes Sperm
(1n = haploid)
Zygote
(fusion)
Haploid and Diploid Chromosomes
CQ4: 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
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
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.
CQ5: 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.
CQ6: During Meiosis II:
A: Homologous chromosomes separate.
B: The DNA is replicated.
C: Gametes fuse.
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.
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: 23
2= 529 combinations.
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
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?
CQ8: Could Santhi have an
XX karyotype and be male?
A: No, an XX individual is always female.
B: Yes, this is common.
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
Crossing Over
• Crossing over
can occur anywhere along
the autosomes.
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.
How is Sex Characterized in
Humans?
In addition to anatomy, physiology, and
chromosomes, there is a 4
thanswer:
Genes:
Specific genes determine
SRY (Sex- Determining Region of the
Y chromosome) Gene
• Early in development, the
immature gonads of males and females are indistinguishable.
• 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.
SRY gene
X
Can you have an XX male or XY
female?
• Watch this video:
http://www.hhmi.org/biointeractive/media/meiosis-lg.mov
