Transcript Epistasis is not dominance.

Other Inheritance Patterns
Intermediate Inheritance
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The heterozygote has a phenotype that
is intermediate between the phenotypes
of the two homozygotes.
Example: Petal color in certain flowers.
Codominance
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The heterozygote expresses both traits
at the same time.
In this example, the heterozygous
chickens are speckled. They express
both feather colors at the same time.
CBCB x CBCB
CWCW x CWCW
CBCW x CBCW
CBCB x CBCW
CBCB x CWCW
CBCW x CWCW
Sex-Linked Inheritance
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Genes located on sex chromosomes
produce different patterns in males and
females.
Females generally have two alleles for
these genes.
Males generally have only one allele.
If a male inherits a sex-linked recessive
allele from his mother, the allele will be
expressed.
Red/Green Color Blindness
Epistasis
Effects of one gene override or mask the
phenotype of a second gene.
Epistasis is not dominance.
Compare the definitions:
Epistasis: One gene masks the expression of
a different gene for a different trait
Dominance: One allele masks the expression
of another allele of the same gene
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Example of Epistasis
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Labrador retrievers can be black,
brown, or yellow. Two genes control
this.
One gene influences melanin production
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B (black) is dominant to b (brown)
One gene influences melanin deposition
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E (full deposition) is dominant to e
(reduced deposition)
Polygenic
Inheritance
Continuous variation
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Most traits show a range of variation
rather than distinct either/or types
This occurs when multiple genes and
environmental factors influence the
trait’s expression
Continuous variation is often described
with frequency distribution tables.
Example using actual data