1. Exceptions to Mendel’s Discoveries

2. Trait – several possible forms of a character
Gene – factor that determines traits
Allele – form of a gene
Hybrid – offspring of parents with different traits

3. Blood type gene consists of 3 alleles: A, B, O
Multiple Alleles
When there are 3 or more forms of an allele for a gene
No individual has more than two alleles, but there are more than two possible alleles in a population, so a trait will be expressed in more than two forms.
Example: Blood Types
Blood type gene consists of 3 alleles: A, B, O
AA  Type A BO  Type B
BB  Type B AO  Type A
   OO  Type O AB  Type AB

4. Codominance Both alleles are dominant and both will be expressed
Example: Blood Type
The A allele is not dominant over the B allele or vice versa.
When both are present, both are equally expressed  AB blood type

5. Codominance Andalusian chickens also show this pattern of inheritance.
If you cross a black (BB) chicken
With a white (WW) chicken
You get black+white speckled (BW) chicken

6. Incomplete Dominance
In incomplete dominance, neither allele is __________ so there is a blending of ______ when two different alleles for the same trait occur together.
Colors blend together
(______________ individuals = rd phenotype)
dominant
traits RR Rr rr
heterozygous
red
pink
white

7. Incomplete Dominance RR
In another flower, if red ____ and blue ____ flowers are crossed, they produce a 3rd purple ____ flower
What would be the genotype ratio and phenotype ratio if you crossed two purple flowers? RR rr Rr

8. Incomplete Dominance Cross of two purple flowers ____ X ____
What are gamete possibilities?
genotype ratio
1RR : 2Rr : 1rr
phenotype ratio
1red : 2 purple : 1 blue
Can you have a heterozygous red or hybrid blue flower? ___ Rr Rr R r RR Rr R
red
purple rr Rr r
purple
blue no

9. Polygenic Traits When a single trait is controlled by several genes.
 Show a wide range of phenotypes
The phenotype is produced by the interaction of more than pair of genes.
Example: Human skin color
Hair color
eye color