Human Genetics – Studying Chromosomes

& Diseases

Biology

A picture of a person’s paired chromosomes, arranged in order from largest to smallest

Karyotype

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

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

Where do the chromosomes come from?

Amniocentesis (for fetus)Cells in the fluid around the unborn

baby are analyzed

Embryo after cleavageA single cell is removed from the embryoPerformed for in vitro fertilization

Problems with MeiosisChromosomes fail to separate properlyResults in too few or too many chromosomes in offspringOften fatal, but some exceptions

How do chromosome problems occur?

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