1. Human Genetics
Ch. 14

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

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

5. 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

6. 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?

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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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