Sex Determination-Nuclear Sexing

Klinefelters syndrome

Barr body

Routine microscopy of mammalian cell nuclei reveals a small, dense mass of heterochromatin present in females but not males. This “sex chromatin” (or Barr body or X-chromatin) is one of the two X chromosomes present in females.

As a general rule, only 1 X chromosome functions in a cell at a given time. All other X chromosomes present in a cell may be seen as X-chromatin bodies in a resting nucleus.

Thus, if one knows the number of X chromosomes, one can anticipate that the number of Barr bodies will be 1 less. If one counts the number of Barr bodies, the number of X chromosomes can be determined by adding 1. Hence Barr bodies are not seen in genotype XO.

The male cell has one X chromosome and one Y chromosome, therefore no sex chromatin is visible in males.

Ref: Manipalviratn S., Trivax B., Huang A. (2013). Chapter 3. Genetic Disorders & Sex Chromosome Abnormalities. In A.H. DeCherney, L. Nathan, N. Laufer, A.S. Roman (Eds), CURRENT Diagnosis & Treatment: Obstetrics & Gynecology, 11e.

A i.e. Interphase

The inactive X can be seen in the interphase nucleus as a darkly staining small mass in contact with the nuclear membrane known as the Barr body or X chromatin. Barr body is the inactivated X chromosome. In non dividing interphase cells it remains tightly coiled and can be seen as a dark staining body within the nucleus.

Ans. is ‘b’ i.e., 45 X0 genome

Barr body (Sex – chromatin)

o It is a densely staining inactivated condensed ‘X’ chromosome that is present in each somatic cells of female.

o It is found in the nucleus.

o It is used as a test of genetic femaleness it is possible to determine the genetic sex of an individual according as to whether there is a chromatin mass present on the inner surface of the nuclear membrane of cells with resting or intermitent nuclei. Remember following fact and the question will seem very easy.

• Chromatid body (Barr body or sex chromatin) is derived from one of the two X-chromosomes which becomes inactivated.
• The numer of Barr bodies is thus one less than the number of X-chromosomes.

Note –

o  Barr body is found in female But –

o  Kleinefelter syndrome is male with Barr body.

o  Turner syndrome is female without Barr body.

Answer is C (46, XXY) :

The patient in question depicts a hypogonadic male that occurs when there are two or more X chromosomes, (47XX Y) and one Y chromosome, and represents the clinical picture of klinefelter’s syndrome.

None of the options appear technically correct as an extra X chromosome in the male should increase the total number of chromosomes to 47 and hence 47 XXY should be the most appropriate answer.

Within the available options however an extra X-chromosome is the most essential aspect and hence the best answer here is 46 XXY.

Klinefelter’s Syndrome: 47 XXV or 46 X,Y / 47 XXY Mosaicism

• Small firm testes: Hyalinization of seminiferous tubules and azoospermia
• Gynaecomastia
• Lack of secondary male characters such as deep voice, beard, male distribution of pubic hair 
• Distinct body habitus: Elongated body: Abnormally long leg
• The mean IQ is some what lower than normal but mental retardation is uncommon 
• Hypogonadism and in fertility
• Klinefelter’s syndrome is produced by non disjunction during meiotic divisions

Ans. A i.e. XXY

Ans. Brain

Product of SRY gene is sex-determining region Y protein.

This protein is involved in male sexual development.

Ans. is ‘b’ i.e., Turner

Barr body (Sex – chromatin)

• It is a densely staining inactivated condensed ‘X’ chromosome that is present in each somatic cells of female. o It is found in the nucleus.
• It is used as a test of genetic femaleness -4 it is possible to determine the genetic sex of an individual according as to whether there is a chromatin mass present on the inner surface of the nuclear membrane of cells with resting or intermitent nuclei. Remember following fact and the question will seem very easy.
• Chromatid body (Barr body or sex chromatin) is derived from one of the two X-chromosomes which becomes inactivated.
• The numer of Barr bodies is thus one less than the number of X-chromosomes.