Mistakes in Meiosis

Non-Disjunction•a type of mistake in meiosis that happens to the CHROMOSOME

•It is the failure of homologous chromosomes to separate properly

2 things can happen

•a) Have extra chromosomes

•b) Missing chromosomes

Extra Chromosomes•EX: Down Syndrome•When chromosome # 21 does not fully separate, and there is an additional chromosome

•A person with down syndrome has 3 chromosomes instead of 2, which is called Trisomy 21

Extra Chromosome

•EX: Polyploidy•Polyploidy is when there is a total LACK of separation of homologous chromosomes

•The gamete (sperm/egg) inherits an entire EXTRA set of chromosomes

Polyploidy•Polyploidy is rare in animals, but if it occurs it will result in death of a zygote

•BUT, it is frequent in PLANTS•Plants that have polyploidy are larger, healthier, and are of greater commercial value

Polyploidy

Missing Chromosomes•If a chromosome is missing, the organism will most likely not survive

•It is referred to as “monosomy”

•EX: Turner syndrome

Turner Syndrome•Human females have only 1 single X chromosome instead of 2 X’s

How to detect Genetic Disorders•Cells are extracted from a

person•The Cells are stained to reveal a banding patterns

•Chromosomes are identified, and arranged in homologous pairs

•This chart is called a Karyotype, and is used to detect chromosomal abnormalities

•Chromosome PAIRS 1 -22 are called Autosomes

•Chromosome Pair 23 is called the sex chromosome

•XX is female•XY is Male •Sperm determines the sex of a baby (meaning it’s either X or Y), while the Egg is always X