M endelian Genetics

Austrian Monk Father of Genetics Pea Plant Experiments ( )

Site of Gregor Mendel’s experiment - a garden in the Czech Republic

Mendel ’ s workplace Fig. 2.5

 Mendel stated that physical traits are inherited as “particles”  Mendel did not know that the “particles” were actually Chromosomes & DNA

Terms you need to know:  Trait - any characteristic that can be passed from parent to offspring  Heredity - passing of traits from parent to offspring  Monohybrid cross - cross involving a single trait e.g. flower color  Dihybrid cross - cross involving two traits e.g. flower color & plant height

 Alleles - two forms of a gene (dominant & recessive)  Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R)  Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)  Genotype - gene combination for a trait (e.g. RR, Rr, rr)  Phenotype - the physical feature resulting from a genotype (e.g. red, white) Terms you need to know:

 Homozygous genotype – When the two alleles are same (2 dominant or 2 recessive genes) e.g. TT or tt; also called pure  Homozygous genotype – When the two alleles are same (2 dominant or 2 recessive genes) e.g. TT or tt; also called pure  Heterozygous genotype – When the 2 alleles are different- one dominant & one recessive allele (e.g. Tt);

Parental P 1 Generation = the parental generation in a breeding experiment.Parental P 1 Generation = the parental generation in a breeding experiment. F 1 generation = the first-generation offspring in a breeding experiment. (1st filial generation)F 1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) –From breeding individuals from the P 1 generation F 2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation)F 2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) – From breeding individuals from the F 1 generation

Mendel’s Pea Plant Experiments

Why peas, Pisum sativum?  Can be grown in a small area  Produce lots of offspring  Several generations in a season  Produce pure plants when allowed to self-pollinate  Can be artificially cross- pollinated  Many traits known  Above all, easy to grow

Reproduction in Flowering Plants Pollen contains sperm. Pollen is found on the stamenPollen contains sperm. Pollen is found on the stamen Ovary contains eggs. Found inside the flower. Turns into fruit after fertilization of the egg cells by sperm.Ovary contains eggs. Found inside the flower. Turns into fruit after fertilization of the egg cells by sperm.

Mendel’s Experimental Methods Mendel hand- pollinated flowers using a paintbrush.Mendel hand- pollinated flowers using a paintbrush. He could snip (cut) the stamens to prevent self- pollinationHe could snip (cut) the stamens to prevent self- pollination He kept detailed records to trace traits through the several generationsHe kept detailed records to trace traits through the several generations

How Mendel Began Mendel produced pure strains by allowing the plants to self- pollinate for several generations

Eight Pea Plant Traits Seed shape --- Round (R) or Wrinkled (r)Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or Green (y)Seed Color ---- Yellow (Y) or Green (y) Pod Shape --- Smooth (S) or wrinkled (s)Pod Shape --- Smooth (S) or wrinkled (s) Pod Color --- Green (G) or Yellow (g)Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g)Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a)Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t)Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white (p)Flower color --- Purple (P) or white (p)

Monohybrid Crosses

Punnett Square  Used to help solve genetics problems

Trait: Seed ShapeTrait: Seed Shape Alleles: R – Roundr – WrinkledAlleles: R – Roundr – Wrinkled Cross: Round seeds x Wrinkled seedsCross: Round seeds x Wrinkled seeds RR x rr RR x rr P 1 Monohybrid Cross R R rr Rr Genotype:Rr Genotype: Rr PhenotypeRound Phenotype: Round Genotypic Ratio:All alike Genotypic Ratio: All alike Phenotypic Ratio: All alike

Trait: Seed ShapeTrait: Seed Shape Alleles: R – Roundr – WrinkledAlleles: R – Roundr – Wrinkled Cross: Round seeds x Round seedsCross: Round seeds x Round seeds Rr x RrRr x Rr F 1 Monohybrid Cross R r rR RR rrRr Genotype:RR, Rr, rr Genotype: RR, Rr, rr PhenotypeRound & wrinkled Phenotype: Round & wrinkled G.Ratio:1:2:1 G.Ratio: 1:2:1 P.Ratio: 3:1

F 1 Monohybrid Cross Review  Heterozygous x heterozygous  Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr  Offspring called F 2 generation  Genotypic ratio is 1:2:1  Phenotypic Ratio is 3:1

What Do the Peas Look Like?

Did the observed ratio match the theoretical ratio?Did the observed ratio match the theoretical ratio? The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The larger the sample the more nearly the results approximate to the theoretical ratio

Dihybrid Cross Yellow, Round x Yellow, Round YyRr X YyRr Each parent can produce 4 types of gametes. YR, Yr, yR, yr Cross is a 4 X 4 with 16 possible offspring.

Dihybrid Cross RYRyrYry RYRy rY ry

RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio RYRyrYryRY Ry rY ry