 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

1. Law of Dominance : In heterozygous genotypes, dominant alleles “hide” recessive alleles when both are inherited by an organism.

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.

 Cross a homozygous dominant tall plant with a homozygous recessive short plant.
 Dominant trait = tall
 Recessive trait = short
What letters would you use to represent this cross?
 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
 TT x tt
T
T t
Tt
Tt t
Tt
Tt
 Genotype
0 % TT
100 % Tt
0 % 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 b
Bb bb bb
 Possible Genotype(s)
0 % BB
50 % Bb
50 % bb
 Possible Phenotype
50
50
% brown
% 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
LL
L
L
Ll
Ll l
 Possible Genotype(s)
50 % LL
50 % Ll
0 % ll
 Possible Phenotype(s)
100
0
% long
% short

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
 Possible Genotype(s)
W w
25 % WW
50 % Ww
W WW Ww
25 % ww
 Possible Phenotype(s)
Ww ww 75
25
% wrinkly
% 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
 r = wrinkled
RR x Rr
R
R r
RR Rr
RR Rr
 Possible Genotype(s)
50 % RR
50 % Rr
0 % rr
 Possible Phenotype(s)
100
0
% round
% wrinkled