Human Genetics – Studying Chromosomes & Diseases Biology

Karyotype A picture of a person’s chromosomes, arranged in pairs and ordered from largest to smallest

Why would a doctor perform a karyotype? If the woman is over 35 (eggs are older) If there are chromosome diseases in the family If a child or adult has symptoms of a chromosome disorder If an adult is having a hard time getting or staying pregnant

Where do the chromosomes come from? Blood samples (for adults or infants)

Where do the chromosomes come from? Chorionic Villi Sampling (for fetus) Cells in the “roots” around the unborn baby are analyzed

Amniocentesis (for fetus) Cells in the fluid around the unborn baby are analyzed

Embryo after cleavage A single cell is removed from the embryo Performed for in vitro fertilization

How do chromosome problems occur? Problems with Meiosis Chromosomes fail to separate properly Results in too few or too many chromosomes in offspring Often fatal, but some exceptions

Trisomy 21 – Downs Syndrome Tri = 3, so Trisomy 21 is 3 chromosome 21’s Mental impairment Upward-slanted eyes Slightly flattened facial features

Klinefelter Syndrome Males with 2 X chromosomes (XXY) Male appearance Some feminine traits (breasts, higher pitched voice) Sperm count is low Hormone injections can help

Turner’s Syndrome Have single X but no other sex chromosome (XO) Female appearance Tend to be very short Affects sexual development Hormone injections help

Pre implantation Diagnosis A test used prior to implantation to help identify genetic defects within embryos Checks for chromosomal issues before placing the embryo in the mother Can also be used for gender selection