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Incomplete Dominance vs. Codominance Mrs. Stewart Biology

Standards CLE 3210.4.3 Compare different modes of inheritance.

Lesson Objectives Correctly create and analyze the punnett square results from incomplete and codominant crosses Can identify scenarios of incomplete dominance and codominance successfully

Three types of dominant relationships for alleles Complete dominance Monohybrid crosses Dihybrid crosses Incomplete dominance Codominance

Complete Dominance Standard dominant vs recessive relationship If dominant allele is present – you get dominant phenotype If dominant allele is not present – you get recessive phenotype Ex: Tongue Rolling (RR or Rr = can roll tongue, rr = can’t)

Incomplete dominance One is not completely dominant over the other Instead, heterozygotes will have a blending of the dominant and recessive traits

Incomplete Dominance Heterozygous = Blend/combo of the parent phenotypes Phenotype = number of horns 3 possible phenotypes = incomplete dominance

Incomplete Dominance - Alleles RR = red Rr = pink rr = white If you cross a red flower with a pink flower, what percentage of the offspring will be white? Red?

Codominance Both alleles for a gene are expressed in the heterozygotes – simultaneously (at same time) Neither allele is dominant and they do NOT blend together

Codominant Alleles Since both are dominant and both are seen, we typically write them as different capital letters. WW = white horse GG = gray horse WG = Apaloosa horse (white horse with gray spots)

Plickers Practice Snapdragons are flowers that can be either white, red or pink. How is color inherited? A = complete dominance B = incomplete dominance C = codominance D = none of the above

Plickers Practice Cross a pink snapdragon (Rr) with a pink snapdragon (Rr). What is the probability that the offspring will be white? A = 100% B = 75% C = 25% D = 0%