Chromosomal Disorders

What happens when meiosis goes wrong?

Karyotype

Human Chromosomes• Humans have 46 chromosomes• Two sex chromosomes-

determine an individual’s sex• Females have two copies of the

large X chromosome• Males have one X and a smaller Y

chromosome

Human Chromosomes

• The remaining 44 chromosomes are known as autosomal chromosomes or autosomes

• Males and females are born in a roughly 50:50 ratio

• All human egg cells carry a single X• Half of all sperm carry and X and the other

half carry a Y

Male or Female???

Can you spot what is wrong with this karyotype?

Chromosomal Mutations

• Chromosomal mutations involve changes in the number or structure of chromosomes• Lead to diseases or

disorders

Changes in chromosome structure• Deletion– Part of a chromosome is

lost during cell division– Chromosome is missing

genes• Duplication– Region of chromosome is

repeated• Translocation– Piece of a chromosome

moves to another chromosome

Nondisjunction• Homologous

chromosomes fail to separate during meiosis I

• Sister chromatids fail to separate during meiosis II

OR

Creates gametes with the wrong number of chromosomes!