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?