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Complex Patterns of
Inheritance
Spring 2017
Question
Why do some traits exhibit a large number of
phenotypes?
Answer:
Because the traits are controlled by many genes.
Complex Patterns of Inheritance
Incomplete DominanceWhen neither allele of the parents is completely dominant.
The phenotype of the heterozygous offspring is a mix of
parents.
Example:
Red snapdragons x White snapdragons = pink snapdragons
Complex Patterns of Inheritance
Codominant allelesBoth alleles show equally
Example: black chicken x white chicken => speckled chicken
Multiple alleles-
There are more than two alleles for a genetic trait
Example: a rabbit’s coat color- there are four possible colors
Complex Patterns of Inheritance
Humans have 23 pairs of chromosomes
22 pairs of homologous chromosomes are called autosomes.
The 23rd pair is called the sex chromosomes
These are indicated by X for females and Y for males.
Sex linked traits- traits that are controlled by genes located on sex
chromosomes
Example: Color blindness
Complex Patterns of Inheritance
Polygenic inheritanceInheritance pattern of a trait that is controlled by two or
more genes
Example: Skin color and height
*Nutrition, light chemicals, infectious agents such as
bacteria, fungi, parasites and viruses can all influence how
genes are expressed.
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