BRAINCAKETurner's Syndrome
Turner's syndrome is a condition affecting females in which one X chromosome is missing. Affected individuals have 45 chromosomes: 44 autosomes and a single X chromosome, written 45,X (or XO). It is an example of monosomy.
It usually arises from non-disjunction of the sex chromosomes during meiosis in one of the parents. For example, if the X and Y chromosomes fail to separate in anaphase I during sperm formation, some sperm receive both X and Y and some receive no sex chromosome at all. A sperm with no sex chromosome (22 autosomes only) fertilising a normal egg (22 autosomes + X) gives a zygote with 45 chromosomes and a single X.
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Key terms in this lesson
- monosomy
- A condition in which a cell or organism has only one copy of a particular chromosome instead of two.
- karyotype
- A photograph or image of an individual's chromosomes, arranged in homologous pairs in order of size.
More in Meiosis and Sexual Reproduction
- The Importance of Meiosis
- Chromosome Mutation
- Non-disjunction
- Down's Syndrome
- Spermatogenesis
- Oogenesis
- The Male Gamete
- The Female Gamete
All 28 lessons in Meiosis and Sexual Reproduction · All Edexcel AS-level Biology topics