GENETICS

Gregor Mendel: The Father of Genetics

PUNNETT SQUARES AND HEREDITY

MENDEL

• Austrian Monk• Interested in Biology

• Bred Pea Plants for specific traits• Was able to show that certain traits

were “inherited”—meaning they were passed down from one

generation to the next

Genetics Heredity

BIOLOGICALSTUDY

ofHeredity

Passing on of a characteristic from parents to offspring.

Pea Plants

Reproduce Sexually, which means egg and sperm.

Mendel studied seven traits of pea plants

Setting up a Cross

C C

C C

A A

B

B

A=Parent 1 Alleles

C=Offspring Genotype

B=Parent 2 Alleles

Setting up a CrossBasic Terminology

P1 = Parents

F1 = 1st Generation of Offspring

F2 = 2nd Generation of Offspring

Setting up a CrossBasic Terminology

Dominant Allele:Only need only copy to be expressed phenotypically.

Uppercase letter = dominant allele

Recessive Allele:

Need two copies to be expressed phenotypically.

Lowercase letter = recessive allele

NOTE: Use letter of dominant trait for

cross.

Homozygous Dominant x Homozygous Recessive

Dominant is Round Recessive is Wrinkled

Monohybrid Cross: Seed Shape

R R

R R

r

r

r r

Rr Rr

Phenotype(s):

Parent 1:

Parent 2:

Offspring:

Genotype(s):

Parent 1:

Parent 2:

Offspring:

Round Seed

Wrinkled Seed

Round Seed

R R

r r

R r

Y

Y

y

y

y y

Y y y

Phenotype(s):

Parent 1:

Parent 2:

Offspring:

Genotype(s):

Parent 1:

Parent 2:

Offspring:

Yellow Seed

Green Seed

½ green, ½ yellow

Y y

y y

½ Y y, ½ y y

Heterozygous x Homozygous RecessiveDominant is Yellow Recessive is

Green

Monohybrid Cross: Seed Color

y

y

y

G

G

g

g

Gg g

Phenotype(s):

Parent 1:

Parent 2:

Offspring:

Genotype(s):

Parent 1:

Parent 2:

Offspring:

Green Pod

Green Pod

¾ Green, ¼ Yellow

G g

G g

¼ GG, ½ Gg, 1/4 gg

Heterozygous x HeterozygousDominant is Green Recessive is

Yellow

Monohybrid Cross: Pod Color

g

g

GG G

I

I

I

i

I i i

Phenotype(s):

Parent 1:

Parent 2:

Offspring:

Genotype(s):

Parent 1:

Parent 2:

Offspring:

Inflated Pod

Inflated Pod

Inflated

I i

I I

¼ I I, ¾ I i

Heterozygous x Homozygous DominantDominant is Inflated Recessive is

Constricted

Monohybrid Cross: Pod Shape

i

I

II I

A few things to keep it simple….• Homozygous Recessive (2 recessive alleles)• Homozygous Dominant (1 recessive allele)• Heterozygous (1 dominant, 1 recessive

allele)• Letter for cross is determined by the first

letter of the dominant allele.• Capital Letter always comes first.• Parent #1 Goes across the top of the punnett

square and is mentioned first in the cross.• Parent #2 Goes down the side of the punnett

square and is mentioned second in the cross.