Mendelian GeneticsGregor 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

Round Wrinkled

Yellow Green

Seed Shape

Seed Color

Flower Color

Pod Shape

Pod Color

Purple White

Inflated Constricted

Green Yellow

Flower Position

Stem Height

Axial Terminal

Tall Short

R r

P1

F1

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

P1

F1

What if he had crossed Pp x pp?

Genotype: Phenotype:

Genotype:

Phenotype:

Genotype:

Phenotype:

Genotype:

Phenotype:

Purple Purple

white White

p p

p

P

Pp Pp

pp pp

This F1 Generation ≠ 4 purple flowered plants, therefore the P1 generation must have been PP x pp.

Now, cross two from the F1 generation.

Genotype: Phenotype:

Genotype:

Phenotype:

Genotype:

Phenotype:

Genotype:

Phenotype:

Purple Purple

purple White

P p

p

P

PP 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 flower Terminal 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 _a

_a _a

a a

A

A or a

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).

XR = red eyes Xr = white eyes

XRXR or XRXr

Red eyed female

XrXr

White eyed female

XRYRed eyed male

XrYWhite eyed male

XRXr XRXr

XRY XRY

XR XR

Xr

Y

Cross a homozygous pure red eyed female with a white eyed male. Give the GR and PR results.

GR: 50% XRXr, 50% XRYPR: 50% Red eyed females, 50% Red eyed males