Genetics - Co- and Incomplete Dominance

GENETICS Traits that are not dominant.

Robert Perry MALIBU HIGH SCHOOL

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COMPLETE DOMINANCE

2

INCOMPLETE DOMINANCE

3

CODOMINANCE

COMPLETE DOMINANCE PLAIN OLD MENDELIAN DOMINANT AND RECESSIVE ALLELES LIKE WE’VE DONE BEFORE

CARNATIONS

CARNATIONS

RR Rr rr

Rr

The phenotype of the heterozygote gives you the clue.

Rr

RED is completely dominant over WHITE.

Rr

Let’s cross two of these heterozygous (Rr) RED carnations . . .

Rr

Rr = R r R RR R r Rr r Rr rr

R R r

r

R

r

R r 75% RED carnations; 25% WHITE

INCOMPLETE DOMINANCE NOT

SOMETHING NEW: MENDELIAN DOMINANT AND RECESSIVE ALLELES

+ A pure red rose.

A pure white rose.

NEITHER RED OR WHITE ARE DOMINANT ...SO WE END UP WITH PINK

INCOMPLETE DOMINANCE A PINK rose.

RR

Red

Rr

Pink

rr

White

Let’s cross two of these heterozygous (Rr) PINK roses . . .

Rr

Pink

Pink is a “blending” of red and white.

Red and white are incompletely dominant

Rr = R r R RR R r Rr r Rr rr

R R r

r

R R r

r

1/4 Red 1/2 Pink 1/4 White

R

r

R r 25% RED roses; 50% PINK; 25% WHITE

CODOMINANCE NOT

SOMETHING NEW: MENDELIAN DOMINANT AND RECESSIVE ALLELES AND NOT INCOMPLETE DOMINANCE.

+ A pure black chicken

A pure white chicken

BLACK & WHITE ARE EQUALLY DOMINANT ...SO WE END UP WITH Erminette

CODOMINANCE An Erminette chicken

BB

Black

Bb

Erminette

bb

White

Let’s cross two of these heterozygous (Bb) Erminette chickens:

Bb

Erminette

Erminette has BOTH black and white.

Black and white are CO-DOMINANT

Bb = B b B BB B b Bb b B b bb

B B b

b

B B b

b

1/4 = black 1/2 = Erminette 1/4 = white

B B b

b

25% = black 50%=Erminette 25% = white

Now for some practice problems !