1. Chapter 4: Modification of Mendelian Ratios Allele *Wild-type allele *Mutant allele Conventional symbols for alleles: recessive allele - initial letter of the name of the recessive trait, lowercased and italicized dominant allele - same letter in uppercase

2. F 1 Generation RRrr Gametes P Generation F 2 Generation Sperm Gametes Red White R r Rr Pink R r R r R r RRRr rr Rr Eggs 1 2 1 2 1 2 1 2 1 2 1 2 In incomplete dominance, F 1 hybrids have an appearance in between the phenotypes of the two parents.

3. Homozygous for ability to make LDL receptors Severe disease Mild disease Cell Normal LDL receptor LDL Homozygous for inability to make LDL receptors Heterozygous HH Hh hh GENOTYPE PHENOTYPE Hypercholesterolemia Dangerously high levels of cholesterol in the blood. Is a human trait that is incompletely dominant. Heterozygotes have blood cholesterol levels about 2X normal. Homozygotes have blood cholesterol levels about 5X normal.

4. Codominance: Condition in which the phenotypic effects of a genes alleles are fully and simultaneously expressed in the heterozygote. Example: MN Blood group - red blood cells contain a transmembrane glycoprotein (glycophorin); two different forms of this protein exist, M and N

5. Blood Group (Phenotype) Genotypes Red Blood Cells O A B AB ii IAIBIAIB I B or I B i I A or I A i Carbohydrate A Carbohydrate B Multiple Alleles Examples: *Table 4.1: over 100 alleles at a given locus in Drosophila *ABO Blood group in humans *Characterized by the presence of glycoprotein antigens on the surface of red blood cells *Distinct from the M and N antigens *Also exhibits codomiance

6. Lethal Alleles: Example: Coat color in mice *A = agouti = wild-type allele *A Y = yellow = mutant allele

8. Epistasis Example: In Drosophila, gene:eyeless *Black (B) is dominant to brown (b) *Second gene responsible for allowing pigment to be deposited in hair, C = presence c = absence (colorless)

9. *Gene product interactions

10. –Pleiotropy is the impact of a single gene on more than one character. Pleiotropy Multiple traits (e.g., sickle-cell disease) Single gene

12. Multiple genes Polygenic inheritance Single trait (e.g., skin color) –Polygenic inheritance is the additive effects of two or more genes on a single phenotype.

13. F 1 Generation P Generation F 2 Generation Sperm AABBCC (very dark) Eggs aabbcc (very light) AaBbCc 1 8 1 64 6 15 64 20 64 15 64 6 1 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8