Incomplete & Codominance Biology Honors 8.5

Exceptions to Mendel’s Work Pea plants show complete dominance only Pea plants show complete dominance only Ex: purple flowers are dominant to white flowers Ex: purple flowers are dominant to white flowers PP=purple PP=purple Pp=purple Pp=purple pp=white pp=white Sometimes genetics are more complex than that! (actually, they usually are) Sometimes genetics are more complex than that! (actually, they usually are)

Incomplete Dominance

Blending of traits Blending of traits Neither allele dominates the other Neither allele dominates the other Three genotypes = three phenotypes Three genotypes = three phenotypes Example: Example: RED flower x WHITE flower  PINK flower RED flower x WHITE flower  PINK flower RR = redrr = whiteRr = pink

Incomplete Dominance Make a key to help you! RR = Red Rr = Pink rr = White

Practice, practice, practice! Oompa Loompa can have red (R), blue (r) or purple hair. Purple hair results from the heterozygous condition. Make a "key" showing the genotypes and phenotypes for hair color. Oompa Loompa can have red (R), blue (r) or purple hair. Purple hair results from the heterozygous condition. Make a "key" showing the genotypes and phenotypes for hair color. RR = red RR = red rr = blue rr = blue Rr = purple Rr = purple

Olivia Oompa is married to Odo Oompa and they both have purple hair. What color hair and in what proportion would you expect their children to have? Olivia Oompa is married to Odo Oompa and they both have purple hair. What color hair and in what proportion would you expect their children to have?

Codominance

So far, we’ve look at… Complete dominance Complete dominance One allele always dominates another One allele always dominates another EX: tall (T) dominates short (t) in pea plants (Tt = tall) EX: tall (T) dominates short (t) in pea plants (Tt = tall) Incomplete dominance Incomplete dominance Alleles are blended together when a heterozygous genotype is expressed Alleles are blended together when a heterozygous genotype is expressed EX: red (R) + white (r) flowered plants = pink (Rr) flowered plants EX: red (R) + white (r) flowered plants = pink (Rr) flowered plants

Codominance Both traits are shown Both traits are shown Both alleles are dominant together Both alleles are dominant together red x white  red & white spotted red x white  red & white spotted RR x rr  Rr RR x rr  Rr Think “co-” is together (cooperate, coexist) Think “co-” is together (cooperate, coexist)

Codominance Make a key to help you! Make a key to help you! RR = Red Rr = Roan (red & white) rr = White

Practice, practice, practice In a certain species of frogs, purple legs (L) are dominant to black legs (l), but heterozygous genotype results in purple and black legs. Set up a key to show this. In a certain species of frogs, purple legs (L) are dominant to black legs (l), but heterozygous genotype results in purple and black legs. Set up a key to show this.

A purple and black legged male mates with a black legged female. What is the chance of having purple legged offspring? Show the cross. A purple and black legged male mates with a black legged female. What is the chance of having purple legged offspring? Show the cross.