Download - Punnett Squares
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