Biology · Principles of Inheritance and Variation · NEET
The person is a male. Even though there are two X chromosomes, the presence of a Y chromosome makes the individual male, so the overall body development is masculine. This is because the Y chromosome carries the male-determining gene. But because of the extra X, some feminine features also appear, mainly gynaecomastia (breast development). So the correct NEET answer is: overall masculine development with some feminine features expressed.
The karyotype is 47, XXY. A normal person has 46 chromosomes (44 autosomes + 2 sex chromosomes). In Klinefelter's syndrome there is one extra X chromosome, so the total becomes 47. The sex chromosomes are X, X and Y together. NCERT states it directly: 'an additional copy of X-chromosome resulting into a karyotype of 47, XXY.'
Sterile means the person cannot produce children. In Klinefelter's syndrome the extra X chromosome disturbs normal development of the testes, so healthy sperm are not made. NCERT clearly says 'Such individuals are sterile.' This is a favourite one-line fact NEET tests, so remember: Klinefelter = male + gynaecomastia + sterile.
Gynaecomastia means development of breast tissue in a male. It is a feminine feature. It happens in Klinefelter's syndrome because of the extra X chromosome, which brings in some female-type development even though the person is male. NEET often uses the exact phrase 'overall masculine development... feminine development (development of breast, i.e., Gynaecomastia) is also expressed.'
It is caused by non-disjunction. Non-disjunction is the failure of chromosomes to separate properly during meiosis (gamete formation). Because of this, a gamete carries an extra sex chromosome. If a sperm or egg with an extra X joins normally, the child ends up with 47, XXY. This gain of a single chromosome is called aneuploidy. Klinefelter's is aneuploidy of the sex chromosomes (not autosomes).
It is a chromosomal disorder, not a Mendelian (single-gene) disorder. Mendelian disorders (like haemophilia, sickle cell anaemia, phenylketonuria) are caused by a change in a single gene. Chromosomal disorders like Klinefelter's, Turner's and Down's are caused by a whole extra or missing chromosome. This difference is a common NEET trap.
What is the genetic disorder in which an individual has an overall masculine development, gynaecomastia, and is sterile?
In which genetic condition, each cell in the affected person has three sex chromosomes XXY?
Which of the following statements are correct about Klinefelter's Syndrome? A. This disorder was first described by Landon Down (1866). B. Such an individual has overall masculine development. However, the feminine development is also expressed. C. The affected individual is short statured. D. Physical, psychomotor and mental development is retarded. E. Such individuals are sterile.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
47, XXY. There are 44 autosomes plus three sex chromosomes (X, X and Y), giving a total of 47 chromosomes - one more than the normal 46.
In males. The Y chromosome makes the person male, so development is overall masculine, but the extra X causes some feminine features like gynaecomastia.
Remember three NCERT points: overall masculine development, gynaecomastia (breast development, a feminine feature), and the individual is sterile.
Non-disjunction during meiosis, which produces a gamete with an extra X chromosome. When this joins a normal gamete, the child gets 47, XXY. This gain of a single chromosome is called aneuploidy.
Klinefelter's is a male with an EXTRA X (47, XXY). Turner's is a female with a MISSING X (45, X0). Both are sex-chromosome disorders and both are sterile.
