Non-Mendelian Genetics

1. Non-Mendelian Genetics

2. Non-Mendelian Genetics • Some traits don’t follow the simple dominant/recessive rules that Mendel first applied to genetics. • Traits can be controlled by more than one gene. • Some alleles are neither dominant nor recessive.

3. 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)

4. 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!)

5. Sex-Linked Inheritance

6. Review • 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.

7. 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.

8. Hemophilia • Recessive trait • Disorder where individuals are missing the normal blood clotting protein. • Uncontrolled bleeds from minor cuts or bruises. • Female hemophiliac: XhXh • Female carrier: XhX • Normal: XX • Male hemophiliac: XhY • Normal: XY

9. Colorblindness • Recessive • Inability to see certain colors

10. Duchenne Muscular Dystrophy • Recessive • Progressive weakening and loss of skeletal muscle. • Defective version of gene that codes for muscle protein

11. EXAMPLES!! • 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!**

12. A woman who is homozygous for normal blood clotting marries a man who has hemophilia. What are the chances of them having a son or daughter with hemophilia?

13. Pedigrees -A pedigree is a chart for tracing genes in a family. -When more than one individual in a family is afflicted with a disease, it suggests that the disease might be inherited.

14. Introduction to Pedigree Symbols -Males are represented by squares. -Females are represented by circles. -Filled symbols show individuals who exhibit the trait in question. -A horizontal line between two symbols represents a mating. -A vertical line descends from parents to a horizontal line shared by all their offspring. -A diagonal line through a symbol indicates that person is deceased. -Roman numerals (I, II, III,…) represent generations. -Arabic numerals (1, 2, 3,…) represent the birth order of siblings. -Specific combinations of numerals (like II-3) uniquely identify each individual in the pedigree.

15. Phenotypes are used to infer genotypes on a pedigree. • Autosomal genes show different patterns on a pedigree than sex-linked genes.

16. If the phenotype is more common in males, the gene is likely sex-linked.

17. THE STEPS WHEN INTERPRETING A PEDIGREE CHART -Determine if the pedigree chart shows an autosomal or X- linked disease. -If most of the males in the pedigree are affected, then the disorder is X-linked -If it is a 50/50 ratio between men and women the disorder is autosomal.

18. -Determine whether the disorder is dominant or recessive. -If the disorder is dominant, one of the parents must have the disorder. -If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.