Monohybrid crosses

A monohybrid cross is a cross between two parents that breed true for different versions of a single trait. In this example, that trait is flower color. The allele that specifies purple flowers is dominant over the allele that specifies white flowers. The purple-flowered plant has two dominant alleles at the locus that governs flower color. It will produce only gametes that carry these alleles. The white-flowered plant has two recessive alleles at the locus that governs flower color. It will produce only gametes that carry these alleles. We can use this Punnett square to predict the probable gamete combinations and genotypes of the offspring. This shows the predicted first generation, or El, genotypes. And theses are the Fl phenotypes. In all offspring, the dominant allele will mask the recessive allele and the offspring will be purple. Now suppose two of the F1 plants are crossed. Once again, we can use a Punnett square to predict the genotypes of the offspring. There are two phenotypes, and the ratio of dominant to recessive phenotypes is 3 to 1.

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