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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

Modified by Liz Murray for IST 341

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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.

Following her silver medal performance, her sex was officially questioned.

Caster Semenya

• Caster Semenya, 18, the world champion 800-meter runner in 2009

• muscular, husky-voiced, extremely fast

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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.

• 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.

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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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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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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.

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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)

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

Human Karyotype

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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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SEXMom 46 chromosomes Dad

(2n = diploid)

Egg 23 chromosomes Sperm

(1n = haploid)

Zygote

(fusion)

46 chromosomes again!

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Haploid and Diploid Chromosomes

Haploid with two chromatidsHaploid with one chromatid

Diploid with one chromatid Diploid with two chromatids

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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.

161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180

181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200

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During Meiosis II:

161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180

181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200

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 X-bearing 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

eggXX XY

XX XY

girls boys

X

X

Y

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.

• 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 generates variation

Recombination (crossing over)

• Occurs in prophase of meiosis I

• Generates diversity

• Group of genes on one chromosome are called the haplotype.

Recombination creates chromosomes with new combinations of alleles for genes A to F.

a

b

c

d

e

f

A

B

C

D

E

F

A

B

C

D

E

F

a

b

c

d

e

f

• Occurs in prophase of meiosis I

• Generates diversityLetters denote genes Case denotes alleles

A

B

C

D

E

F

a

b

c

d

e

f

c

d

e

f

A

B

a

b

C

D

E

F

Recombination

Recombination creates chromosomes with new combinations of alleles for genes A to F.

• Occurs in prophase of meiosis I

• Generates diversity

Letters denote genes Case denotes alleles

A

B

C

D

E

F

a

b

c

d

e

f

c

d

e

f

A

B

a

b

C

D

E

F

Recombination creates chromosomes with new combinations of alleles for genes A to F.

Recombination (crossing over)

Recombination creates chriamata

The two sources of genetic variation in meiosis are independent assortment and genetic recombination.

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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.

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.

Oogonium(diploid)

Mitosis

Primaryoocyte(diploid)

Meiosis I

Secondaryoocyte(haploid)

Meiosis II

(if fertilizationoccurs)

First polar bodymay divide (haploid)

Polarbodiesdie

Ovum (egg)

Secondpolar body(haploid)

a

A

X

X

a

X

A X

a

X

a

X

Matureegg

A

X

A

X

Oogenesis

• One of four meiotic products becomes an ovum.

• The three remaining meiotic products are polar bodies.

Ovum Formation

Oogenesis vs spermatogenesis

Meiosis lasts much longer in oogenesis in humans

• 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.

Fertilization

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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.

• 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

Y

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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.

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.”

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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.

What About Caster

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