Animal Genetics:
Dominant vs. Recessive
Traits
Intro to Agriculture Science
GOALS:
 Explain the difference between dominant and
recessive genes.
 Use a Punnett Square to predict genotypic and
phenotypic ratios of offspring.
What do we already know?
review…
Phenotype
 Appearance!
 Result of Genotype
Example:
Bw = Black Coat
Because
B is dominant
Genotype
 The genetic makeup!
 Alleles from parents
 What you can’t see
Example:
Alleles that code for
good milk production.
Alleles
 A pair of genes
 That code for the same trait
Example:
Hair Color
Eye Color
Height
What do we need to know?
vocabulary…
Dominant Genes
 Determine what the offspring will look like!
 Expressed as capital letters
 Mask recessive genes.
Example:
B=Black
w=White
Dominant Allele = B
Recessive Genes
 Sometimes determine what the offspring will look
like.
 Expressed as lowercase letters
Example:
B=Black
w=White
Recessive allele = w
What is it called
when both alleles are the
same?
 Homozygous
Example
AA or aa
?
?
AA or aa
Identify... Dominant & Recessive
Homozygous
Homozygous
Dominant
Recessive
AA or aa
What is it called
when both alleles are different?
Heterozygous
Example
Aa
Lets Get to It!
Genetic
Crosses
Punnett
Squares
Monohybrid
Crosses
What the heck are they?
 Punnett squares are genetic crosses used by
biologists to predict the probability that certain
traits will be inherited by offspring.
What do they look like?

Punnett Square:
MONOHYBRID CROSS
A Punnett Square
Using one pair of
contrasting traits
Ex: hair color
Example #1:
Homozygous vs. Homozygous
Example #1:
 A White Sow (ww)
crossed with
A Black Boar (BB)
Homozygous vs.
Homozygous
(ww)
w
w
Bw
Bw
Bw
Bw
B
(BB)
B
Example #2:
Homozygous vs. Heterozygous
Example #2:
 A White Sow (ww)
crossed with
A Black Boar (Bw)
Homozygous vs.
Heterozygous
(ww)
w
w
Bw
Bw
ww
ww
B
(Bw)
w
Example #3:
Heterozygous vs. Heterozygous
Heterozygous vs.
Heterozygous
(Bw)
B
w
BB
Bw
Bw
ww
B
(Bw)
w
Result…
Try it!
cfu…