Correct.
The physical characteristics of this athlete are typical of those of a woman, and in 1966 she would have qualified to compete in women's events. Many female athletes don't have menstrual cycles, a condition known as amenorrhea.
Case Studies
Male and female athletes compete in separate events in most sports. Starting in the 1960s, the major international sports organizations adopted standardized tests to verify that athletes competing in women's events are biologically female according to different criteria and therefore eligible to compete in those events.
Since the year 2000, tests have focused on measuring testosterone as the biological basis of men's competitive advantage.
You will travel through time and apply each test to the cases of two fictitious athletes: a sprinter and a swimmer.
Case Study: Sprinter
It’s 1966.
All athletes competing in women's events must undergo a physical exam to qualify to compete. They are required to walk naked before a panel of judges ("naked parades") and/or undergo gynecological examinations. Athletes judged by the panel to have typical female reproductive anatomy are eligible to compete.
Here are the results of the sprinter’s physical exam.
If you were one of the judges in 1966, would you rule that the athlete is eligible to compete in women's events? Select your answer below.
Try again.
The physical characteristics of this athlete are typical of those of a woman, and in 1966 she would have qualified to compete in women's events. The fact that she never had a menstrual cycle would not have disqualified her.
It’s 1968.
Physical exams have been replaced by a less invasive chromosomal test. In cells with two X chromosomes, one is
inactivated and becomes a Barr body, which appears as a darkly stained structure right up against the nuclear envelope. A positive Barr body test qualifies an athlete to compete in women's events.
Here are the sprinter’s Barr body test results.
If you were one of the judges in 1968, would you rule that the athlete is eligible to compete in women's events?
Try again.
The athlete's cells don't have a Barr body. In 1968, these results would have disqualified an athlete from competing in women's events. The reasoning behind this decision is that absence of a Barr body is more consistent with someone who is 46,XY than 46,XX—although we now know that cells of 45,X women also lack Barr bodies.
Correct.
Correct. The athlete's cells don't have a Barr body. In 1968, these results would have disqualified an athlete from competing in women's events.
It’s 1992.
The Barr body test has been replaced by testing for a gene on the Y chromosome called SRY. Scientists isolate DNA from the athlete's blood cells. They
amplify a section of SRY DNA using polymerase chain reaction (PCR) and analyze the PCR sample by
gel electrophoresis. Presence on the gel of a DNA band corresponding to SRY would disqualify an athlete from competing in women's events.
Here is an image of the gel for the sprinter.
If you were one of the judges in 1992, would you rule that the athlete is eligible to compete in women's events?
Try again.
If you look in lane 4, which contains the sprinter's DNA, there is a PCR product corresponding to the SRY gene. In 1992, presence of an SRY gene in an athlete's DNA would have disqualified the athlete from competing in women's events. The reasoning behind this decision is that a functional SRY gene is important for testes development and the production of large amounts of testosterone.
Correct.
If you look in lane 4, which contains the sprinter's DNA, there is a PCR product corresponding to the SRY gene. In 1992, presence of an SRY gene in an athlete's DNA would have disqualified the athlete from competing in women's events.
It’s 2011.
Sports officials have abandoned routine sex testing of female athletes. Current policies call for measuring blood testosterone in some athletes, if suspicions are raised about their sex. The cutoff for being able to compete in women's events is less than
10 nmol of testosterone per liter of blood. These policies are based on the claim that higher levels of naturally produced testosterone are responsible for men's athletic advantage.
Here is the testosterone measurement for the sprinter.
If you were one of the judges in 2011, would you rule that the athlete is eligible to compete in a women's event?
Testosterone level: 25 nmol/L
Try again.
In 2011, athletes with blood testosterone levels above 10 nmol/L would not qualify to compete in women's events. This athlete's testosterone levels are 25 nmol/L.
Correct.
In 2011, athletes with blood testosterone levels above 10 nmol/L would not qualify to compete in women's events. This athlete's testosterone levels are 25 nmol/L.
Summary Questions
These are all of the sprinter's test results. Based on the data, how would you characterize this athlete's biological sex?
| Physical Exam |  Presence of typical female sex characteristics |
 Absence of typical female sex characteristics |
|---|---|---|
| Barr Body Test | Barr body present |
Barr body absent |
| PCR Test | SRY gene absent |
SRY gene present |
| Testosterone | Above 10 nmol/L |
Below 10 nmol/L |
Female
There is no right or wrong answer for this question. This athlete has some characteristics of a typical biological female (female external reproductive anatomy and secondary sex characteristics) and some characteristics of a typical biological male (no Barr body, a functioning SRY gene, and high testosterone levels).
Male
There is no right or wrong answer for this question. This athlete has some characteristics of a typical biological female (female external reproductive anatomy and secondary sex characteristics) and some characteristics of a typical biological male (no Barr body, a functioning SRY gene, and high testosterone levels).
I don't know
There is no right or wrong answer for this question. This athlete has some characteristics of a typical biological female (female external reproductive anatomy and secondary sex characteristics) and some characteristics of a typical biological male (no Barr body, a functioning SRY gene, and high testosterone levels).
Which of the following genetic variations could result in an individual who has female external reproductive anatomy and secondary sex characteristics, but also appears to have a functioning SRY gene and high testosterone level?
I need to see the phenotypes chart again
Some of the more common DSDs are shown below.
Click on the chromosome(s) for each variation to learn about the phenotype.
-
46,XX
Typical biological female
-
46,XX
CYP21A2 gene mutation
-
46,XY
SRY gene mutation
- 45,X
-
46,XY
AR gene mutation
- 47,XXY
-
46,XX
SRY gene present
-
46,XY
SRD5A2 gene mutation
-
46,XY
AMH or AMHR2 gene mutations
-
46,XY
Typical biological male
Try again.
Someone who is 46,XX is most likely have a Barr body and no SRY gene.
Try again.
Someone who is 45,X would not have a Barr body, like this athlete, but would be unlikely to have an SRY gene.
Correct!
Based on the choices provided, the phenotype is most consistent with a 46,XY individual with androgen insensitivity. They would not have a Barr body, have a functioning SRY gene, and high testosterone, but without a functioning androgen receptor, testosterone does not affect cells. Individuals with androgen insensitivity can have typical external female reproductive anatomy and secondary sex characteristics. Since they don't have functioning ovaries, they do not have menstrual periods. Under more recent regulations, this athlete would actually be allowed to compete because although they have high testosterone levels, their body does not appear to respond to the hormone as indicated by the female reproductive anatomy.
Try again.
Someone who is 46,XY would most likely not have a Barr body, like this athlete. The mutation in the SRY gene could affect the PCR test and give a negative result for the SRY gene. In addition, if the testes do not develop, it is less likely that this athlete would have high testosterone levels. There is a more likely explanation for this phenotype.
Inactivated
One of the two X chromosomes is inactivated, which means that the genes on this chromosome are not expressed (e.g., do not produce RNA and proteins). X chromosome inactivation ensures that all individuals—female and male—have only one functional copy of the X chromosome in each cell. If inactivation did not occur, cells with two X chromosomes would express a potentially harmful double dose of certain genes.
Amplify
Polymerase chain reaction (PCR) results in millions of copies, or amplified numbers, of a specified DNA region.
Gel electrophoresis
Gel electrophoresis is a method used to separate mixtures of DNA, RNA, or proteins by size and charge using an electric field and a gel matrix with small pores. Smaller pieces of DNA (or RNA, or proteins) will move through the gel matrix more quickly than larger pieces. Markers of known sizes are also run in the gel alongside the samples; in the case of DNA, the size markers are referred to as a DNA ladder.
10 nmol (nanomoles) per liter
A mole is an amount of a substance, specifically 6.022 x 1023 atoms of that substance. 10 nanomoles per liter is equivalent to one hundred-millionths of a mole, or 6.022 x 1015 atoms, in a liter of fluid. This measurement was chosen as a cut-off for participating in women's events because most female athletes have values well below 10 nmol/L. More recent guidelines have imposed a cutoff of 5 nmol/L in certain events.
Testosterone measurement
Testosterone levels can be measured in blood samples using immunoassay: a technique for determining the concentration of a substance using antibodies. Another common method for measuring testosterone levels uses mass spectrometry.
Biological sex
Biological sex is defined by an individual's combination of chromosomes, hormone levels, internal and external reproductive anatomy, and sex characteristics. It is usually treated as a binary trait: female or male. Biological sex is different from gender, which is based on social and cultural ideas of what it means to be a woman or man. Gender identity refers to an individual's concept of who they are. Gender identity does not always match biological sex.
Phenotype
The term phenotype refers to the observable characteristics or traits of an individual. Phenotype is the result of the interaction of the genetic makeup of an individual and environmental factors.
Typical biological female
In typical biological females, the SRY gene is absent. Phenotype: female internal and external reproductive anatomy and secondary sex characteristics, although there are variations among individuals (for example, variations in breast size or muscle mass); estrogens are typically much higher than testosterone, but there is variation in hormone levels and also in the body's response to hormones.
CYP21A2 gene mutation
CYP21A2 mutations can alter the production of steroid hormones and cause enlargement of the adrenal glands, a condition known as congenital adrenal hyperplasia. Since the adrenal glands are a source of androgens, 46,XX individuals with this condition can produce excess testosterone and other hormones. Phenotype: ovaries present and functional; uterus present; enlarged clitoris; short vaginal canal; elevated testosterone levels (a condition referred to as hyperandrogenism); decreased fertility. Individuals are typically assigned to a female sex at birth.
SRY gene mutation
Mutations in the SRY gene may inactivate its function, and errors in chromosome segregation during meiosis may result in deletion of the SRY gene from the Y chromosome. Without a functioning SRY gene, the gonads do not differentiate into testes. Phenotype: uterus and fallopian tubes are present; ovaries are present but they do not produce eggs; typical female external sex characteristics. Individuals are typically assigned to a female sex at birth.
An error in chromosome segregation during meiosis results in only one complete X chromosome, with the other X chromosome being partially or completely missing. The condition is known as Turner syndrome. Phenotype: highly variable among affected individuals based on the extent and region of the missing X chromosome; female external reproductive anatomy; absent or reduced secondary sex characteristics; infertility; and ovaries may be absent or nonfunctional (e.g., do not produce eggs). Individuals are typically assigned to a female sex at birth.
AR gene mutation
To have an effect on cells, testosterone has to bind to a receptor called the androgen receptor (AR). Some mutations in the AR gene result in cells that don't respond to testosterone. The resulting condition is called androgen insensitivity syndrome. Phenotype: female or ambiguous external reproductive anatomy; male or ambiguous internal anatomy; breasts may develop. Individuals with complete androgen insensitivity syndrome are typically assigned to a female sex at birth, but there is a spectrum of phenotypes depending on the type of AR gene mutation involved.
An error in chromosome segregation during meiosis can cause an individual to have two X chromosomes and a Y chromosome. This condition is known as Klinefelter syndrome. Phenotype: male internal and external reproductive anatomy; low testosterone levels (hypoandrogenism); small testes; infertility; weak muscles; breasts may develop. Individuals are typically assigned to a male sex at birth.
SRY gene present
The SRY gene may be present on one of the X chromosomes as the result of crossing over between the X and Y chromosomes during meiosis. Phenotype: male external reproductive anatomy; small testes; low testosterone (hypoandrogenism); infertility. Individuals are typically assigned to a male sex at birth.
SRD5A2 gene mutation
Mutations in the SRD5A2 gene cause a deficiency in the enzyme 5-alpha reductase. Developing embryos do not produce enough of a hormone called dihydrotestosterone that is important for male sex development. Phenotype: male internal reproductive anatomy; female or ambiguous external reproductive anatomy at birth; surge in testosterone at puberty results in mostly male sex characteristics. Individuals may be assigned to either male or female sex at birth, but often reassign their sex to male after puberty.
AMH or AMHR2 gene mutations
In males, binding of the anti-Müllerian hormone (AMH) to its receptor, AMHR2, prevents the development of the Müllerian ducts into uterus and fallopian tubes. Mutations in the AMH and AMHR2 genes interfere with this process, resulting in the development of uterus and fallopian tubes. Phenotype: male internal and external reproductive anatomy, along with uterus and fallopian tubes; high testosterone; male secondary sex characteristics. Individuals are typically assigned to a male sex at birth.
Typical biological male
SRY gene is present. Phenotype: male internal and external reproductive anatomy and secondary sex characteristics, although there are variations among individuals (for example, variations in penis size, muscle mass, or facial hair); testosterone is typically much higher than estrogens, but there is variation in hormone levels and in the body's response to hormones.