Punnett Squares

Punnett Squares A Punnett square illustrates how the

parents’ alleles might combine in offspring. The top of the Punnett Square are one of the

parent’s alleles, the side of the Punnett square shows the other parent’s alleles for the trait

Heterozygoushaving dissimilar pairs of alleles for any

hereditary characteristic

Homozygoushaving identical pairs of alleles for any

given pair of heredity characteristics

Mendel’s Laws of Inheritance1. Law of Dominance: In heterozygous genotypes,

dominant alleles hide recessive alleles when both are inherited by an organism. (Hh means the dominant trait will show up in the phenotype)

WHY?

Mendel’s Laws of Inheritance

1. The Law of Segregation (separation): Each organism has 2 alleles for a gene. Only one allele from each gene pair will be passed on to the offspring.

Homozygous/Heterozygous

Cross a homozygous dominant tall plant with a homozygous recessive short plant.

What letters would you use to represent this cross?

Dominant trait = tall Recessive trait = short

T = tall t = short

Hmzg / Htzg

What is the genotype of a homozygous dominant tall plant?

Genotype%

TT%

Tt% tt

TT

TT x tt

What is the genotype of a homozygous recessive short plant? tt

t t

T

T

Phenotype% tall%

short

Tt Tt

Tt Tt

0100

0

0100

2. Cross a heterozygous brown haired rabbit with a homozygous recessive white haired rabbit.

oWhat letters would you use to represent this cross?

Dominant trait = brown hair

Recessive trait = white hair

B = brown

b = white

What is the genotype of a heterozygous brown haired rabbit?

Genotype%

BB%

Bb%

bb

Bb

Bb x bb

What is the genotype of a homozygous recessive white haired rabbit? bb

b b

B

b

Phenotype%

brown%

white

bb bb

Bb Bb

0 50

50

50 50

3.. Cross a homozygous dominant long haired guinea pig with a heterozygous long haired guinea pig.

oWhat letters would you use to represent this cross?

Dominant trait = long hair

Recessive trait = short hair

L = long

l = short

What is the genotype of a homozygous dominant long haired guinea pig?

Genotype%

LL%

Ll% ll

LL

LL x Ll

What is the genotype of a heterozygous long haired guinea pig? Ll

L l

L

L

Phenotype% long%

short

LL Ll

LL Ll

50 50

0

0100

4. Cross a heterozygous wrinkly elephant with another heterozygous wrinkly elephant.

What letters would you use to represent this cross?

Dominant trait = wrinkly skin

Recessive trait = smooth skin

W = wrinkly

w = smooth

What is the genotype of a heterozygous wrinkly-skinned elephant?

Genotype%

WW%

Ww%

ww

Ww

Ww x Ww

What is the genotype of a heterozygous wrinkly-skinned elephant? Ww

W w

W

w

Phenotype%

wrinkly%

smooth

Ww ww

WW Ww

25 50

25

25 75

Phenotype% round%

wrinkled

5. A plant that is homozygous dominant for round seeds is crossed with a heterozygous plant. What is the probability that the offspring will have wrinkled seeds?

RR x Rr

R r

R

R

RR Rr

RR Rr

R = round

Genotype%

RR% Rr% rr

r = wrinkled

50 50

0

0 100