Transcript Punnett Squares

Punnett Squares
Punnett Squares
Illustrates how the parents’ alleles might
combine in offspring.
 One parent’s alleles are placed down the
side of the square, the other parent’s alleles
are placed along the top

 Heterozygous: having different alleles for
a hereditary character
 Homozygous: having identical alleles for
a heredity character
Mendel’s Laws of Inheritance
1. 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
Hmzg / Htzg

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


What is the genotype of a homozygous
dominant tall plant?  TT

What is the genotype of a homozygous
recessive short plant?  tt

T
TT x tt
t
t
Tt
Tt

Genotype
0 % TT
100 % Tt
0 % tt

T
Tt
Tt
Phenotype
100 % tall
0 % short
2. Cross a heterozygous brown haired rabbit
with a homozygous recessive white haired
rabbit.
What letters
would you use to
represent this
cross?

Dominant trait = brown hair
(B)

Recessive trait = white
(b)

What is the genotype of a heterozygous
brown haired rabbit?  Bb

What is the genotype of a homozygous
recessive white haired rabbit?  bb

Bb x bb
b
b
B
Bb
Bb
b
bb
bb
Possible Genotype(s)
0 % BB
50 % Bb
50 % bb
 Possible Phenotype
50 % brown
50 % white

3.. Cross a homozygous dominant
long haired guinea pig with a
heterozygous long haired guinea pig.
What letters
would you use to
represent this
cross?

Dominant trait =
long hair (L)

Recessive trait =
short hair (l)

What is the genotype of a homozygous
dominant long haired guinea pig?  LL

What is the genotype of a heterozygous
long haired guinea pig?  Ll

LL x Ll
L
l
L
LL
Ll
L
LL
Ll
Possible Genotype(s)
50 % LL
50 % Ll
0 % ll
 Possible Phenotype(s)
100 % long
% short
0

4. Cross a heterozygous wrinkly
elephant with another heterozygous
wrinkly elephant.
What letters
would you use to
represent this
cross?

Dominant trait =
wrinkly skin (W)

Recessive trait =
smooth skin (w)
What is the genotype of a heterozygous
elephant?  Ww
 What is the genotype of a heterozygous
elephant?  Ww


Ww x Ww
W
w
W
WW
Ww
w
Ww
ww
Possible Genotype(s)
25 % WW
50 % Ww
25 % ww
 Possible Phenotype(s)
75 % wrinkly
25 % smooth

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?
 R = round

RR x Rr
R
r
R
RR
Rr
R
RR
Rr
r = wrinkled
Possible Genotype(s)
50 % RR
50 % Rr
0 % rr
 Possible Phenotype(s)
100 % round
0 % wrinkled
