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Mendellian and Human

(Campbell/Reese.  Biology:6th Ed. Copyright 2002 Pearson Ed. Inc.)


Offspring can be predicted using a Punnett Square (a probability tool).  Online tutorial can be found at:

If P=Purple (and is dominant) and p=yellow (and is recessive)

All genotypes would be Pp.  All phenotypes would be purple.

Genotype Ratio is 2PP: 2Pp.  All phenotypes would be purple.

Genotypic Ratio is 1PP:2Pp:1pp. Phenotypic Ratio is 3:1 purple to yellow.

When two heterozygous organisms are crossed for a single trait, the cross is called a monohybrid cross.

Genotypic Ratio is 1Pp:1pp.  Phenotypic Ratio is 1:1 purple to yellow.

graphics from


Dihybrid Punnett Square