Exceptions to Mendel’s laws Variations in Genetics
1) Incomplete dominance Some alleles are not completely dominant and the offspring will have a “blending” of the parents’ traits. EX: Red flower x White flower Pink flowers
2) Codominance 2 alleles are equally dominant and both are expressed in the offspring. EX: Roan horses and cows really have white & red hair (appear brownish). Both hair colors show up when a white horse is bred to a “red” horse. Some flowers have both pink and white equally dominant and you get pink/white flower color in the flowers.
Codominance
3) Multiple Allele Traits A trait that has more than just 2 types of alleles. EX: human blood types** (also show codominance). You have alleles A,B,O. A and B are both dominant. They are dominant to O as well.
Blood Typing Genotypes If you are type A, you can have genotypes AA or AO. If you are type B, you can have genotypes BB or BO. If you are type 0, your genotype is OO. If you are AB, your genotype is AB.
Blood Type Problems Solve these: 1.Can a man with type B blood and a woman with type A blood have a baby that is type O? 2.Can a man with type 0 blood and a woman with type AB have a baby that is type 0? 3.A type A man and a type AB woman have a baby. Indicate all the possible blood types of their children.
Solving the problems
4) Polygenic Traits A trait that is controlled by more than 1 gene. EX: human skin color, height, and eye color These are difficult to solve with Punnett squares. You can get tons of variations from them.
5) Sex linked traits (X- linked) Some traits are found on the sex chromosomes instead of autosomes and are more likely to show up in one gender. EX: colorblindness & hemophilia **these traits generally affect males more than females.
Solving sex linked traits A man with hemophilia and a woman that carries hemophilia have 4 children. Predict if each child is normal blood, a carrier of hemophilia or has the disease. H-normal blood h- hemophilia Ex. The man: XY- X h Y The woman: XX- X H X h
The Punnett Square Solution
You try this one A colorblind woman marries a man who is not colorblind. Colorblindness is a recessive sex linked trait. Indicate which of their children will be colorblind.