Human Genetics Ch. 14

Quick Review 46 chromosomes 22 pairs of autosomes 1 pair of sex chromosomes XX = ♀ XY = ♂ 30,000+ genes 3,100,000,000 bases

Pedigrees Diagram used to show how traits are inherited in a family Like a genetic family tree

Blood Types Multiple alleles – IA, IB, i Blood Type Genotype Antigen on RBC Donate blood to Receive blood from A IAIA, IAi A, AB A, O B IBIB, IBi B, AB B, O AB IAIB A and B A, B, AB, O O ii none

Blood Types Two couples had babies in the same hospital at the same time and the babies got mixed up. Doctors determine whose baby is whose using blood type analysis. The Johnson couple has blood types of B and AB; the Smith couple has blood types of B and A. Baby 1 has a blood type of A and Baby 2 has a blood type of O. Which baby belongs to which couple?

Cystic Fibrosis Most common in Northern Europeans and their descendants 1/2500 births Recessive disorder Lungs clog with mucus, digestive problems

Sickle Cell Anemia Most common in Africans and their descendants Protects against malaria Malaria protist can’t infect sickle cells Better to be heterozygous, than to not carry the sickle cell allele in areas with malaria

Sex-linked Traits X-chromosome carries 100s of genes Since males only have one X, they show X-linked recessive alleles more often than females Ex – hemophilia, colorblindness, muscular distrophy

Sex-linked Cross What are the odds of a son being colorblind if his mom’s dad was colorblind, but his mom and dad were normal? XBXb x XBY

Boy or Girl? Y chromosome produces a protein that shuts off the X chromosome Leads to male development Females only need one X, so extra X is shut off at random in each cell Turned off X called a Barr body Leads to calico cats

Extra Chromosomes?! Nondisjuction in gametes – during metaphase I, sometimes the homologous chromosomes don’t separate Usually lethal, except in chr. 21 and sex chr. (13 & 18 rarely trisomy) Extra 21 – Trisomy 21 or Down Syndrome

Sex Chromosomes  Turner Syndrome – XO Sterile, underdeveloped female Klinefelter’s Syndrome – XXY, XXXY Sterile, long arms and legs, shy Triple X – XXX Fertile, taller than average