1. Genetics… What Mendel never knew!

2. Incomplete dominance Book definition: When one allele is not completely dominant over another allele The heterozygous indidvidual produces a phenotype different than either type of homozygous (dom/rec) Aa looks different than AA or aa Results in a “mixture” of phenotypes Ex: A new color; not seen in either parent

5. Look at the F2 generation…what is the ratio of phenotypes?

6. Codominance Book definition: when both alleles contribute to the phenotype of the individual. Neither allele “covers up” the other In the phenotype both characteristics are seen…flowers with red AND white petals. In the heterozygous individual you will see both parental phenotypes.

10. Codominance: Chickens with both black and white feathers.

11. Multiple alleles Book definition: more than two alleles (>2) for a given gene determine a trait HOWEVER,NO INDIVIDUAL HAS MORE THAN TWO ALLELES For some reason in the population there exist more than two gene choices Weird interactions go on between the alleles; some are dominant over others, some are codominant, etc.

12. Multiple alleles: human blood type Three alleles: A, B, & O A is dominant over O B is dominant over O Therefore O is recessive to both A & B A and B are codominant Remember: no one person has more than two of the thee alleles.

15. Rabbit fur color: multiple alleles (four alleles) C, C ch, C h, c

16. Polygenic traits Book definition: a trait controlled by more than one gene pair. Not just a pair of alleles (Rr), but at least two (RrTt) that work together on one trait. These alleles or gene pairs don’t result in an either/or phenotype, but a range of phenotypes…the smallest to the biggest. Phenotypes of many different forms Examples: human height, skin color, etc

17. Skin color

18. Human height

19. Other polygenic traits Any trait with a “bell curve”: two extreme phenotypes and everything in between… Birth weight Eye color Others????

20. Pleiotropic: NOT IN OUR BOOK… Definition: when a pair of alleles has multiple effects. Because the one pair of genes codes for a protein that may not work correctly …the effects are seen throughout the body.

23. Bottom line… Not all inheritance follows the simple rules of dominance and recessive Incomplete dominance Codominance Multiple alleles Pleiotropic polygenic