Download Complex Traits

Complex Traits
1. Rules of Inheritance
• Some traits follow the simple rules of
Mendelian Inheritance of dominant and
recessive genes.
• Complex traits follow different patterns of
inheritance that may involve multiple genes
and other factors. For example
– Incomplete or blended dominance
– Codominance
– Multiple Alleles
– Polygenic traits
2. Incomplete Dominance
• In Incomplete Dominance, every genotype has
its own phenotype. (One allele is not
completely dominant over the other)
• This creates a third phenotype that is a blend
of the parental traits. (2 alleles produce 3
phenotypes)
- Result: Heterozygous
phenotype somewhere
between homozygous
phenotype
RR
RW
WW
Incomplete Dominace
R R
R W
RR RW
R
W
WW
RW
RW
RW
W
W
RW RW
3. Codominance
• In Codominance neither alleles are dominant;
both are expressed. A cross between
organisms with two different phenotypes
produces offspring which has both
phenotypes of the parental traits shown.
4. Multiple Alleles
• When more than 2 different alleles exist for
the same trait.
– Remember: each individual will only have two
alleles for a trait but there are several alleles to
choose from.
– Ex., human blood type has 3 different allele
variants: A, B & O.
– In humans, blood type has multiple alleles. IA and
IB are codominant and i (type O) is recessive
5. Polygenic Traits
• The inheritance pattern is controlled by 2 or
more genes each with two alleles.
• Polygenic inheritance usually shows up as a
range of variation such as height, skin color or
hair color.
• The results of a large population will result in
a bell-shaped curve.
Type of Dominance?
Type of Dominance?
Type of Dominance?