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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