Punnett SquaresPunnett Squares

Punnett Squares

Illustrates how the parentsIllustrates how the parents’’ alleles might alleles might combine in offspring. combine in offspring.

One parent’s alleles are placed down the One parent’s alleles are placed down the side of the square, the other parent’s alleles side of the square, the other parent’s alleles are placed along the topare placed along the top

HeterozygousHeterozygous: having : having differentdifferent alleles for alleles for a hereditary charactera hereditary character

HomozygousHomozygous: having : having identicalidentical alleles for alleles for a heredity charactera heredity character

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

dominant alleles “hide” recessive alleles when both are inherited by an organism.

Mendel’s Laws of Inheritance

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

Homozygous/Heterozygous

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

What letters would you use to represent this cross?

Dominant trait = tall Dominant trait = tall

Recessive trait = shortRecessive trait = short

T = tall T = tall t = short t = short

Hmzg / Htzg

What is the genotype of a homozygous What is the genotype of a homozygous dominant tall plant?dominant tall plant?

GenotypeGenotype

% % TTTT

% % TtTt

% tt% tt

TT TT

TT x ttTT x tt

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

t t

T

T

PhenotypePhenotype

% tall% tall

% short% shortTt Tt

Tt Tt

0

100

0

0

100

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

What letters would you use to

represent this cross?

Dominant trait = brown hairDominant trait = brown hair (B) (B)

Recessive trait = white (b) Recessive trait = white (b)

What is the genotype of a heterozygous What is the genotype of a heterozygous brown haired rabbit?brown haired rabbit?

Possible Genotype(s)Possible Genotype(s)

% BB% BB

% Bb% Bb

% bb% bb

Bb Bb

Bb x bbBb x bb

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

b b

B

b

Possible PhenotypePossible Phenotype

% brown% brown

% white% whitebb bb

Bb Bb

0

50

50

50

50

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

What letters would you use to

represent this cross?

Dominant trait = Dominant trait = long long hairhair (L) (L)

Recessive trait = Recessive trait = short hair (l)short hair (l)

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

Possible Genotype(s)Possible Genotype(s)

% LL% LL

% Ll% Ll

% ll% ll

LLLL

LL x LlLL x Ll

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

L l

L

L

Possible Phenotype(s)Possible Phenotype(s)

% long% long

% short% shortLL Ll

LL Ll

50

50

0

0

100

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

What letters would you use to

represent this cross?

Dominant trait = Dominant trait = wrinkly skin (W)wrinkly skin (W)

Recessive trait = Recessive trait = smooth skin (w) smooth skin (w)

What is the genotype of a heterozygous What is the genotype of a heterozygous elephant?elephant?

Possible Genotype(s)Possible Genotype(s)

% WW% WW

% Ww% Ww

% ww% ww

WwWw

Ww x WwWw x Ww

What is the genotype of a heterozygous What is the genotype of a heterozygous elephant?elephant? WwWw

W w

W

w

Possible Phenotype(s)

% wrinkly% wrinkly

% smooth% smoothWw ww

WW Ww

25

50

25

25

75

Possible Phenotype(s)

% round% round

% wrinkled% 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 RrRR x Rr

R r

R

R

RR Rr

RR Rr

R = round

Possible Genotype(s)Possible Genotype(s)

% RR% RR

% Rr% Rr

% rr% rr

r = wrinkled

50

50

0

0

100