Download Learning Punnett Squares

Punnett Squares:
Dominant &
Recessive Traits
Gregor Mendel
is often called
the “Father of
Genetics”.
He studied the
heredity of pea
plants & was the
first to identify
dominant &
recessive traits.
Our focus will be
on the following 3
traits: Height,
Color, and Pea
Texture.
• Our focus will be on the following 3 traits:
• Height
• Color
• Pea Texture
A CAPITAL letter
is used to
represent a
dominant allele
while a lower case
letter represents a
recessive allele.
Trait
Height
Color
Dominant Recessive
trait
trait
Tall (T)
Short (t)
Green (G) Yellow (g)
Pea
Smooth (R) Wrinkled(r)
texture
The physical
appearance or trait
that is visible, like
freckles or dimples,
is known as the
phenotype.
The actual gene
combination or
alleles that
determine a trait
is known as the
genotype.
Offspring inherit
one allele of a
genotype from
each parent.
If an organism
carries two dominant
alleles (TT) or two
recessive alleles (tt)
for a trait they are
said to be purebred
or homozygous.
“homo”
=
same
An organism that
carries both a
dominant allele & a
recessive allele (Tt)
for a trait is called a
hybrid or
heterozygous.
“hetero”
=
different
In a
heterozygous
mix, the
dominant trait
will mask the
recessive trait.
Some traits are
determined by
several genes & are
therefore hard to
predict in offspring,
for example, height,
hair color & eye color
in humans.
Alleles
GG
Gg
gg
Genotype Phenotype
Homozygous
dominant
green
Heterozygous
green
Homozygous
recessive
yellow
A table called a
Punnett square can be
used to predict the
genotypes &
phenotypes offspring
will have based on the
genotypes or traits of
the parents.
**Unless noted
otherwise, use
the following
rules:
Mom’s genes will be first in a
cross (ladies first) & should go on
the left of a Punnett square.
Dad’s genes will be last in a cross
& should go on the top of a
Punnett square.
Capital letter is written BEFORE
the lowercase letter in a
heterozygous genotype.
G = green
g = yellow
GG X Gg
Mom
Dad
G
g
G
GG
Gg
G
GG
Gg
Mom
Dad
G = green
g = yellow
GG X gg
Mom
Dad
g
g
G
Gg
Gg
G
Gg
Gg
Mom
Dad
Genotypes (%)
GG: 0%
Gg: 100%
gg: 0%
G = green
g = yellow
Phenotype ratio: 4:0
G = green
g = yellow
Gg X Gg
Mom
Dad
G
g
G
GG
Gg
g
Gg
gg
Mom
Dad
Genotypes (%)
GG: 25%
Gg: 50%
gg: 25%
G = green
g = yellow
Phenotype ratio: 3:1
r
r
R
Rr
Rr
R
Rr
Rr
Mom
Dad
R = Smooth
r = Wrinkled
Genotypes (%)
Homozygous dominant: 0%
Homozygous recessive:
0%
Heterozygous:
100%
Phenotype ratio: 4:0
R
r
R
RR
Rr
r
Rr
rr
Mom
Dad
R = Smooth
r = Wrinkled
Genotypes (%)
Homozygous dominant: 25%
Homozygous recessive: 25%
Heterozygous:
50%
Phenotype ratio: 3:1
r
r
R
Rr
Rr
r
rr
rr
Mom
Dad
R = Smooth
r = Wrinkled
Genotypes (%)
Homozygous dominant: 0%
Homozygous recessive: 50%
Heterozygous:
50%
Phenotype ratio: 2:2
R
R
R
RR
RR
R
RR
RR
Mom
Dad
R = Smooth
r = Wrinkled
Genotypes (%)
Homozygous dominant:100%
Homozygous recessive:
0%
Heterozygous:
0%
Phenotype ratio: 4:0