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Variations of Inheritance Patterns
Chapter 10, Section 3
The Complexity of Inheritance
• Mendel studied simple characteristics in pea plants and was able to define some basic principles behind their inheritance patterns
• However, many characteristics visible in organisms have more complex inheritance patterns than those studied by Mendel
Intermediate Inheritance (Incomplete Dominance)
Cr Cr
Cw CrCw
Pink
CrCw
Pink
Cw CrCw
Pink
CrCw
Pink
Neither allele is dominant over the other, therefore the heterozygous phenotype is an intermediate (or BLEND) of the two homozygous phenotypes
Codominance
Both alleles are visible in the heterozygous phenotype
Ex: Roan Coat (both red and white hairs) AB blood (both A and B antigens)
HR HR
HW HRHW
Roan
HRHW
Roan
HW HRHW
Roan
HRHW
Roan
Multiple Alleles
When there are more than 2 alleles in the population
Ex: Blood Type (IA, IB, i)
Coat color in Rabbits
(C, cch, ch, c)
Phenotype Genotype
A IAIA, IAi
B IBIB, IBi
AB IAIB
O ii
Polygenic Inheritance
When two or more genes control the trait
The more genes that control the trait, the more variation in phenotypesEx: Height, eye color, skin color in
humans
Feather color in parakeets
Green Blue Yellow White
BBYY BByy bbYY bbyy
BbYY Bbyy bbYy
BBYy
BbYy
The Environmental Influence
Environmental factors (such as temperature, sun exposure, altitude, diet, exercise, etc.) can have significant effects on the phenotypes of certain organisms
In general, the product of a genotype is not typically a defined phenotype, but rather a range of possibilities influenced by the environment.