THE INHERITANCE OF HUMAN TRAITS
HUMAN BLOOD GROUPS
Some genes can have three or more alleles: multiple alleles
Important to remember that only two alleles are present in a 2N cell.
ABO blood groups:
Austrian physician Karl Landsteiner classified blood into four groups
based on the presence or absence of specific chemical substances.
The presence or absence of A and B antigens give us four different
blood types: A,B,AB, & O.
Because of the blood types, transfusions can be tricky.
The ABO blood groups are determined by a single gene w/3 alleles.
See fig. 11-5
Rh blood groups: If Rh antigens are present you are Rh positive, w/0 it
you are Rh negative.
ABO and Rh are grouped together: AB- or O+ (+ is dominant over -)
BLOOD TYPES
DISEASES
HUNTINGTON DISEASE (Chromosome #4)
Produced by a single dominant allele
No symptoms until 30-40; then gradual damage to nervous system until
loss of muscle control and mental function.
SICKLE CELL ANEMIA
Dr. James Herrick noticed a black student w/ unusual symptoms
Red blood cells are shaped like a sickle instead of being round & flat
Cause: change in one of the polypetides found in the hemoglobin
Genetics: The allele for normal hemoglobin (H”A”) is codominant w/
the sickle cell allele (H”S”). So, H”A”H”S” are carriers, and H”S”H”S”
are sufferers.
DISORDERS
MOLECULAR
Molecular basis: The allele for sickle cell hemoglobin differs from
normal by a single nucleotide
So, the substitution of one nucleotide in the allele results in the sub.
Of a different amino acid making hemoglobin less soluable in blood.
Distribution: African descent most common carriers in USA
Rest of world; tropical regions of Africa and Asia. 10% of Americans
and 40% of some African areas carry the trait.
Why so common in some parts and not others: Anemia parallels the
disease of malaria. Sickle cell anemia has persisted wherever it has
helped its carriers survive malaria. (evolution idea)
POLYGENIC TRAITS: Traits controlled by a number of genes.
Height, body weight, skin color
Skin color controlled by 4 different genes controlling the melanin.
POLYGENIC TRAITS