Course: Science Subtest II
Lesson: Genetics and Evolution
Topic: Inheritance of Traits      Page 14 of 18  

Incomplete Dominance

In some cases, two alleles express an intermediate form of a trait. For example, if a red snapdragon flower is crossed with a white snapdragon, the first generation (F1) of offspring will all express pink flowers (an intermediate form).

Yet if the pink F1 generation is crossed with itself, the second generation (F2) of offspring will have red, pink, and white flowers. So, even though the F1 generation expressed a phenotype of pink, its genotype contained heterozygous forms of some of the alleles.

A Punnett square is a diagram that is used to predict the outcome of a particular cross or breeding. Biologists use punnet graphs to determine the probability that offspring will have a particular genotype. In the case below. dominant homozygote are crossed with recessive homozygote, the offspring will be heterozygous.

F1  generation

  RR RR
WW WR WR
WW WR WR

F2 generation

  W R
W WW WR
R WR RR

Incomplete Dominance