Karyotyping Chromosomes are extracted from a cell, stained, photographed and paired for genetic analysis in the lab. Karyotypes are used to identify chromosomal disorders.

Karyotypes are prepared with metaphase cells.

46 chromosomes identify a karyotype as human. 44 of the chromosomes are called autosomes 2 of the chromosomes are sex chromosomes –XX for females –XY for males

Fertilization Males can contribute an X or a Y. Females can only contribute an X, because they have 2X’s. Who determines the sex of the zygote (offspring)?

Normal Human Karyotype

Nondisjunction When an error occurs in meiosis and the homologous chromosomes fail to separate it is called nondisjunction. Nondisjunction results in the wrong number of chromosomes in a gamete. This wrong number of chromosomes leads to a disorder.

Trisomy 21– Down Syndrome Characteristic facial features, short stature; heart defects Susceptibility to respiratory disease, shorter lifespan Prone to developing early Alzheimer's and leukemia Often sexually underdeveloped and sterile Usually some degree of mental retardation. Down Syndrome is sometimes related to the age of mother, but can also be the result of nondisjunction of the father's chromosome 21.

Down Syndrome Trisomy 21

Klinefelters XXY Male sex organs; unusually small testes, sterile. Breast enlargement and other feminine body characteristics. Normal intelligence.

Triple X Syndrome XXX females. 1:1000 live births healthy and fertile usually cannot be distinguished from normal female except by karyotype

Turners Syndrome XO 1:5000 live births the only viable monosomy in humans women with Turner's have only 45 chromosomes XO individuals are genetically female, however, they do not mature sexually during puberty and are sterile. Short stature and normal intelligence. (98% of these fetuses die before birth)

Gorilla karyotype sex-specific chromosomes, sex chromosomes, occur in many species Non-sex chromosomes are called autosomes

Mouse Karyotype