Patterns Of Inheritance

● Heterozygous (Rr) or Homozygous Dominant (RR)
● WHEN DOMINANT TRAIT IS EXPRESSED
● Example:

○ RR =Red
○ rr = White
○ Rr =Red

1. COMPLETE DOMINANCE

2. INCOMPLETE DOMINANCE

● HETEROZYGOUS
● WHEN TRAITS “BLEND/MIX”
● Example:

○ RR =Red
○ rr = White
○ Rr =Pink

● HETEROZYGOUS
● WHEN “BOTH” ARE EXPRESSED
● Example:

○ RR – Red
○ rr- White
○ Rr – Red and White

3. CODOMINANCE

● Are controlled by two or more

genes (or sets of alleles)

● Show many different

phenotypes

● Ex- Human skin color is

controlled by 4 different
genes

Polygenic Traits

Multiple alleles

● When there are more than 2 alleles (factors) for a trait
● Ex. Blood Types are determined by multiple alleles.
● There are three alleles for blood type.

○ Both A and B are dominant over O.
○ A and B are codominant.

IA , IB , i

Genotype

Phenotype
(blood type)

AA, AO Type A

BB, BO Type B

AB Type AB

OO

Type O

Patterns of Inheritance Video

Blood Typing: "Who's your Daddy?"

● ABO blood typing can be used in paternity cases.
● A child has type A blood (AA or AO) and the mother is

type O and the suspect Father is type O.
○ Is this possible?

● The father has to have at least one A.
● ABO blood typing cannot determine

who is the father, it can only
determine who is not the father.