Genetic ExceptionsIncomplete Dominance, and Codominance
Law of Dominance
• 1st Law – Law of Dominance – Some alleles will be shown while some other alleles will not be shown.
I was wrong??
Incomplete Dominance
• Normally if dominant allele is present then its trait will show however...
• Sometimes offspring have alleles (2 or more) that influence phenotype.
• Phenotype that results is a “blending” of proteins.
• Alleles themselves do not combine, only the characteristics they code for.
Example: Flower Color
Red (R) Blue (r)
All F1= Heterozygous (Rr) F2 = 1 RR : 2 Rr : 1 rr
All Heterozygous genotypes will show the blending of phenotypes. NOT MIXING ALLELES, MIXING PROTEINS!
R R
r
r
Rr Rr
Rr Rr
R r
R
r
RR
rr
Rr
Rr
Codominance
• Shared dominance. Two dominant alleles code different proteins.
• No true dominant alleles. -R’ = represents the codominant allele• No blending of characteristics.-All dominant proteins are coded.
Example 1: Coat color
R= brownR’= black
R R’
R
R’
RR
R’R’
RR’
RR’
Example 2: Sickle Cell
R= RoundR’= Sickle R R’
R
R’
RR RR’
RR’ R’R’
Example 3: Blood Types • 3 alleles code for blood type: IA IB and i(type O)
• A is codominant with B and both are expressed: Type AB• A is dominant over O : Type AA or AO• B is dominant to O : Type BB or BO• O is recessive: Type OO
Pedigrees and Sex-linked traits
Pedigrees A diagram that traces the inheritance of a
particular trait through several generations
-Normal Male -Normal Female
-Male w/ Trait -Female w/ Trait
-Male who is a -Female who is a
carrier of trait carrier of trait
Roman numerals- Generations
- Siblings
-Generation
I
II
III
Sex-Linked Trait Traits that are controlled by genes located on
the X chromosome
Also known as X-linked traits
Males are affected more often because they only have one X chromosome.
Females must have it on both X chromosomes to show the trait.
Females with only one effected X chromosome are considered carriers
EX. Hemophilia
Cross a male without hemophilia with a female who is a carrierXHY x XHXh
What is the chance of producing a boybaby with hemophilia?