Sex Chromosome Abnormalities

Failure of separation of homologous chromosomes or sister chromatids during meiosis, resulting in gametes with an abnormal number of chromosomes, is called 'non-disjunction'.

Sex chromosome abnormalities are disorders caused by an abnormal number of sex chromosomes in an individual. They usually arise due to non-disjunction, a process in which chromosomes fail to separate properly during meiosis.

As a result, gametes may carry extra or fewer chromosomes than normal. When such gametes participate in fertilization, the zygote formed has an abnormal chromosome number, leading to characteristic developmental and reproductive features.

Karyotype: 47, XXY (trisomy of sex chromosomes).

Sex: Male.

Main features:

• Tall stature and long limbs.
• Underdeveloped testes; reduced/absent spermatogenesis → infertility.
• Sparse body hair, sometimes breast enlargement.
• May have learning difficulties or language/reading problems.

Karyotype: 45, XO (monosomy of sex chromosomes).

Sex: Female.

Main features:

• Short stature.
• Webbed neck and broad chest.
• Poorly developed ovaries → reduced secondary sexual characters → infertility.
• Often delayed puberty.

• Sex chromosome abnormalities are due to non-disjunction causing gain or loss of X/Y chromosomes.
• Klinefelter’s syndrome: 47, XXY, male, tall, underdeveloped testes, low sperm/infertility.
• Turner’s syndrome: 45, XO, female, short stature, webbed neck, broad chest, underdeveloped ovaries, infertility.