Mendelian Genetics Gregor Mendel Monk Lived in modern-day Czech Republic “father of modern genetics” Wrote a famous paper called Experiments on plant hybridization In mid-1800s, he studied heredity in pea plants

7 traits of pea plants studied RoundWrinkled YellowGreen Seed Shape Seed Color Flower Color Pod Shape Pod Color Purple White Inflated Constricted GreenYellow Flower Position Stem Height Axial Terminal TallShort Rr

P1P1 F1F1

Which color is dominant? A purple and white plant are crossbred The resulting peas are planted All four F1 generation plants are purple Which allele do you think is the dominant allele? Remember: each parent donates 1 allele to each offspring P1P1 F1F1

What if he had crossed Pp x pp? Genotype: Phenotype: Genotype: Phenotype: Genotype: Phenotype: Genotype: Phenotype: Purple whiteWhite pp p P Pp pp This F 1 Generation ≠ 4 purple flowered plants, therefore the P 1 generation must have been PP x pp.

Now, cross two from the F1 generation. Genotype: Phenotype: Genotype: Phenotype: Genotype: Phenotype: Genotype: Phenotype: Purple purpleWhite Pp p P PP Pp pp The white flowers show back up—the gene wasn’t lost. It was just hidden!!!

If the phenotype is a recessive trait, the organism must be ___ for that trait. homozygous recessive (aa) If the phenotype is a dominant trait, the organism could be ____ or ___ for that trait. Homozygous dominant (AA) or heterozygous (Aa) aaAA or Aa Gene: flower position Possible Allele Combinations: Axial position of flowerTerminal position of flower

Think through it… If the offspring have a phenotypic ratio of 4 axial: 0 terminal then the genotype of the dominant parent must be AA If the genotype of the dominant parent is Aa, then the phenotypic ratio of the offspring is 2 axial: 2 terminal _a aa A A or a

Now you try: In a test cross, a plant with inflated pods (and unknown genotype) was crossed with a plant with constricted pods. 120 peas from this cross were planted. The F 1 generation resulted in 120 plants with inflated pods and 0 plants with constricted pods. What are the genotypes of the P 1 generation? I I X ii

Law of Segregation—alleles for a trait separate in forming eggs and sperm !

Independent Assortment Animation Law of Independent Assortment— alleles for different traits are distributed to eggs and sperm independently !!!

Law of Independent Assortment—alleles on separate chromosomes assort independently

Incomplete Dominance—a blend is obtained

Codominance—Roan color horse-- Red and white hairs! Red Roan Black and white hairs! Blue Roan

Incomplete Dominance OR CoDominance

SEX LINKED TRAITS FRUIT FLIES

Some alleles are located on the sex chromosomes instead of the autosomes (chromosome pairs 1-22 for humans). These traits are called sex-linked traits. Fruit fly eye color is determined by an allele on the X chromosome. Fruit fly eyes may be red(R) or white(r). X R = red eyes X r = white eyes X R X R or X R X r Red eyed female XrXrXrXr White eyed female XRYXRY Red eyed male XrYXrY White eyed male

XRXrXRXr XRXrXRXr XRYXRYXRYXRY XRXR XRXR XrXr Y Cross a homozygous pure red eyed female with a white eyed male. Give the GR and PR results. GR: 50% X R X r, 50% X R Y PR: 50% Red eyed females, 50% Red eyed males