Fr. Gregor Mendel Father of Genetics

Pre-Mendelian Ideas on Inheritance Blending Homunculus

Why was Mendel Successful? 1. Good Research Organism (pea plant) * Small, easy to grow in large numbers * short life cycle  could test several generations * Could cross or self-pollinate

Could cross or self-pollinate (Why was this important????)

Why was Mendel Successful? 1. Good Research Organism (pea plant) * Small, easy to grow in large numbers * short life cycle  could test several generations * Could cross or self-pollinate * Were “politically correct” (Explain!)

Why was Mendel Successful? 1. Good Research Organism (pea plant) 2. Had good math/statistical background 3. Picked good pairs of traits to study: ex: Tall/short ex: (find for HW!)

Mendel’s Experiments Experiment #1 Created “pure breeding” tall plants Created “pure breeding” short plants

Experiment #1 (cont) Crossed “pure” tall x “pure” short

Experiment #1 (cont) Crossed two F1 plants (Monohybrid Cross!)

Now we know….

Same pattern w “pure-breeding” purple & white:

Same Pattern:

Mendel’s Conclusions Organisms inherit two “factors” for each trait, one from each parent Principle/Law of Dominance Principle/Law of Segregation Law of Independent Assortment (Based on next cross…)

Pure Purple Tall x Pure Short White P : F1 F2: (Homework):

Test Cross:  Learn, then explain what it is & why Prof Dillon hates the following diagram:

Text Rep of Test Cross:

Extensions to Mendel Incomplete dominance Co-dominance Pleiotrophy Polygenetic inheritance

Incomplete Dominance In snapdragons, R  red petals r  white petals GenotypePhenotype RR  Rr  rr 

Incomplete Dominance GenotypePhenotype RR  Red petals Rr  rr 

Incomplete Dominance GenotypePhenotype RR  Red petals Rr  rr  White petals

Incomplete Dominance GenotypePhenotype RR  Red petals Rr  Pink petals! rr  White petals

Incomplete Dominance If you mate a red with a white snapdragon… 1) RR X rr 2)

Incomplete Dominance If you mate a red with a white snapdragon… 1) RR X rr 2) R r

Incomplete Dominance If you mate a red with a white snapdragon… 1) RR X rr 2) R r Rr (= 100% pink!) r R

Co-dominance

Co-dominance I A  type A markers on surface of RBC I B  type B markers on surface of RBC i  neither A nor B markers on surface of rbc

Co-dominance Genotype  Phenotype Type A Blood Type B Blood Type O blood

Co-dominance Genotype  Phenotype I A I A or I A iType A Blood Type B Blood Type O blood

Co-dominance Genotype  Phenotype I A I A or I A iType A Blood I B I B or I B iType B Blood Type O blood

Co-dominance Genotype  Phenotype I A I A or I A iType A Blood I B I B or I B iType B Blood iiType O blood

Co-dominance Genotype  Phenotype I A I A or I A iType A Blood I B I B or I B iType B Blood iiType O blood I A I B  ??

Co-dominance Genotype  Phenotype I A I A or I A iType A Blood I B I B or I B iType B Blood iiType O blood I A I B  Type AB blood!

Co-dominance

Polygenetic Each allele  melanin deposition The more genes, the more pigment (melanin).

Remember: Environment influences Phenotype Same genotype!!