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Chapter 7.1 & 7.2

In incomplete dominance, neither allele is completely
dominant nor completely recessive.
B = Blue and b = Green
BB = Blue
bb = green
Bb = Teal
When both alleles are present (heterozygous) the
traits blend
Sometimes, you may use two different letters
Example: B = Blue G= Green

In codominance, both alleles are dominant.
B = Yellow and b = Black
BB = Yellow
bb = black
Bb = Yellow & Black
When both alleles are present (heterozygous) then
both traits show
Sometimes, you may use two different letters
Example: Y = Yellow B= Black
 In
Flying Pigs
A = Red
a = Blue
• If the trait was normal inheritance, what would the
phenotype be for a “Aa”?
Red Pig
• If the trait was Codominant, what would the phenotype
be for a “Aa”?
Red & Blue Pig
• If the trait was Incomplete Dominance, what would the
phenotype be for a “Aa”?
Purple Pig
 Polygenic
traits are
produced by two or
more genes.
 Example –
AaBbCCDd code for
one phenotype
Order of dominance:
brown > green > blue.
• An epistatic gene can interfere with other genes.
– For example – in Labs you can have either a Black,
yellow or chocolate lab
B = Black b= Chocolate
BUT a = yellow and it is epistatic, which means if the dog
inherits a “a” the dog is yellow, it doesn’t matter what if
they are BB, Bb, bb
What color is the dog?
AaBb
aaBb
Aabb
Black
aabb
Yellow
Yellow
Chocolate
• Phenotype is a combination
of genotype and
environment.
• The sex of sea turtles
depends on both genes
and the environment
• Height is an example of a
phenotype strongly affected
by the environment.