I.Introductory Definitions A.Heredity: passing traits from parents to offspring B.Genetics: study of heredity C.Chromosomes:rod-shaped, coiled DNA; transmits hereditary info D.Genes: units of heredity located on chromosomes E.Allele: one form of a gene

II. Mendel’s Pea Plants A. 1850s B. Why pea plants? 1. Lots of offspring 2. Grow quickly 3. Self-pollinate (offspring identical to themselves) 4. Cross-pollinate (2 parents) C. Studied 7 traits (e.g. tall/short) by controlling pollination

D. Mendel’s experiments 1. P (parental) generation a) 14 pure strains (ex: pure tall) 2. F 1 generation a) Hybrids: offspring from crossing opposite pure strains b) Ex: breed tall with short 3. F 2 generation 1. Offspring from self-pollinating F 1 generation

E. Mendel’s results 1. F 1 generation a) One trait always disappeared b) Ex: tall X short --> all tall 2. F 2 generation a) “invisible” trait reappeared b) Ex: F 1 tall X F 1 tall --> 3 / 4 tall & 1 / 4 short

P Generation F1 Generation F2 Generation TallShortTall Short

F. Mendel’s conclusions 1. Traits controlled by pairs of genes (FACTORS) 2.Principle of Dominance: one gene in a pair may mask the other (tall masks short gene) a) Dominant allele = capital letter (T = tall) b) Recessive allele = small letter (t = short)

c) Possible pair combinations: Homozygous (purebred): both genes in pair identical  Homozygous dominant: TT  Homozygous recessive: tt Heterozygous (hybrid): one dominant & one recessive: Tt

3. Principle of segregation: each pair of genes (alleles) separates when sex cells are formed (MEIOSIS) each F 1 plant produces two different gametes (Tt --> T gamete & t gamete) 4. Principle of Independent Assortment: gene pairs separate independent of other gene pairs

III. Punnett Square A. Diagram that shows the gene combinations that might result from a cross B. Genotype: the gene combination of an individual Ex: TT, Tt, tt C. Phenotype: physical traits as determined by the genotype Ex: TT & Tt= tall, tt = short

Genotype: 100% Ee Phenotype: 100% long ears

D. Monohybrid cross 1. single genetic trait 2. Each parent will pass on one allele to the offspring 3. Each offspring will have 2 alleles (one from each parent)

Monohybrid Cross 1 / 4 TT: 2 / 4 Tt: 1 / 4 tt 3 / 4 Tall : 1 / 4 Short

E. Dihybrid cross 1. Two genetic traits 2. Each parent will pass on one allele from each gene 3. Each offspring will have 2 pairs of alleles (2 alleles from each parent)

4. Since the parents in a dihybrid cross are heterozygous, there are 4 different combinations of alleles (gametes) they can pass on to their offspring: RY RrYy Ry rY ry

Dihybrid Cross 9/16 Round yellow 3/16 Round green 3/16 Wrinkled yellow 1/16 Wrinkled green 9:3:3:1

IV. Beyond Dominant & Recessive A. Incomplete dominance -One allele is not completely dominant 1. Heterozygous phenotype is between the two parent phenotypes 2. Ex: red X white --> pink

Red X white 4 / 4 pink

B. Codominance 1. both alleles are expressed in the phenotype 2. Ex: red X white --> roan (red & white both present)

P generation F 1 generation F 2 generation

C. Multiple alleles: gene with more than 2 possible alleles 1. Each individual inherits only 2 2. Examples: Blood types (A B o ) + Rabbit Coats (C ch h c )

D.Polygenetic traits: some characteristics are controlled by two or more gene pairs 1. Wide range of phenotypes 2. Ex: skin color, eye color, Human Height “Labrador Coat Colors –Epistasis”