Non-Mendelian Genetics BECAUSE SOME TRAITS DON’T FOLLOW THE SIMPLE DOMINANT/RECESSIVE RULES THAT MENDEL FIRST APPLIED TO GENETICS.

Incomplete Dominance  One allele is not completely dominant over another.  The heterozygous phenotype is a blending of the two homozygous phenotypes. Example: four o’clock flowers  rr=red  ww=white  rw=pink (blending of the two alleles)

Codominance  Two alleles are both expressed as a dominant phenotype  Coat color in cows  RR: Red  WW: White  RW: Roan, white with red spots (NOT pink!)

Multiple-Alleles  Codominance  More than two choices of alleles are present for a trait  Example: Human blood  has three alleles: A, B and O  A and B are dominant to O and codominant to each other  If both A and B are present, type is AB  Individuals can be type A, B, AB, or O (recessive)

What are the different blood groups?  Blood group A (I A, I A ), (I A, i) have A antigens on the surface of red blood cells and B antibodies in blood plasma.  Fights off type B RBCs  Blood group B (I B, I B ), (I B, i) have B antigens on the surface of red blood cells and A antibodies in blood plasma.  Fights off type A RBCs

What are the different blood groups?  Blood group AB (I A, I B )  have both A and B antigens on the surface of red blood cells and no A or B antibodies in blood plasma.  Doesn’t fight off any blood (universal blood receiver)  Blood group O (i, i)  have neither A or B antigens on the surface of red blood cells but have both A and B antibodies in blood plasma.  Fights off both type A and B blood  Universal donor

Sex-Linked Inheritance  Males have an X and a Y chromosome  Females have two X chromosomes  These chromosomes determine sex, so genes located on these chromosomes are known as sex-linked genes.  The X chromosome is much larger than the Y, so it carries more genes than the Y chromosome.  Disorders that are sex-linked are much more common in males, because they would only need 1 recessive allele to have the trait; rather than the two recessive alleles the females need.

Hemophilia Recessive trait Disorder where individuals are missing the normal blood clotting protein. Uncontrolled bleeds from minor cuts or bruises. Female hemophiliac: X h X h Female carrier: X H X h Male hemophiliac: X h Y Color Blindness Recessive Inability to see certain colors Female genotype: Female carrier: Male genotype:

 EXAMPLE  A woman who is heterozygous for normal vision marries a man who is colorblind. What are the chances of them having a son or daughter who is colorblind? **NOTE: You have to use X’s and Y’s, and read the punnett square separately for boys and girls!**