Turner Syndrome and Chromosomes

Study Notes

Chromosomal Disorder: Turner Syndrome

A chromosomal disorder affecting females, named after Henry Turner who first described it.
Characterized by the partial or complete absence of one X chromosome in females.

Human DNA and Chromosomes

Human DNA is a blueprint of information on how to make a human, packaged into 46 chromosomes.
The 46 chromosomes come in 23 pairs, each pair containing one chromosome from each parent.
One of these pairs, the sex chromosomes, determines a person's biological sex (XX for females and XY for males).

Meiosis and Sex Cell Formation

Meiosis produces sex cells, and chromosomes replicate, creating an 'X' shape with two copies of DNA.
The cell splits in two, pulling apart paired chromosomes, resulting in two cells with 23 chromosomes each.
The two copies of the chromosome get pulled apart, and the cells split again, resulting in four cells with 23 chromosomes each.

Turner Syndrome: Causes and Karyotype Scenarios

Turner syndrome occurs due to monosomy, where one parent contributes one chromosome less, specifically affecting the X chromosome.
Three potential karyotype scenarios are associated with Turner syndrome:
- Most common: an entire X chromosome is missing, resulting in a 45, X karyotype.
- Less common: mosaicism, where individuals have cells with 45, X and 46, XX karyotypes.
- Rare: ring X chromosome, where the X chromosome is broken and forms a ring shape.

Nondisjunction and its Consequences

Nondisjunction occurs when chromosomes don't split apart during meiosis, resulting in one cell with an extra chromosome and one cell missing a chromosome.
Nondisjunction can happen during the first or second meiotic division, leading to various karyotype scenarios.

Mosaicism and Mitosis

Mosaicism occurs when nondisjunction happens during mitosis, resulting in a mixture of cells with 45, X and 46, XX karyotypes.
Mitosis is the process of cell division that produces every kind of cell in the body.

Description

Learn about Turner syndrome, a chromosomal disorder affecting females, and how chromosomes determine biological sex. Discover how chromosomes are packaged and paired, and what happens when one X chromosome is missing or partially absent.