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For example, plants with purple flowers do not necessarily have
wrinkled pea shapes and vice versa, because the purple flower
trait and the wrinkled pea shape trait are independent from each
other. (This was true in Mendel’s experiments, but cell biologists
later discovered that genes can occasionally be linked and
inherited together.)

LAW OF DOMINANCE

Mendel’s law of dominance defines dominant variants as
those that appear as a trait—as a purple flower or tall stem, for
example—whenever the offspring inherits one copy of the allele.
Recessive variants appear as a trait only when two copies—one
from each parent—are present in the offspring. So a plant that

Punnett squares show how dominant and recessive phenotypes will appear in the
offspring of two hypothetical parent organisms. Here, the dominant phenotypes are
represented by a capital A, and the recessive ones by a lowercase a.

Genetic Concepts Then and Now
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