In roses, red flowers and long stems are dominant traits. A rose plant that is homozygous for both red flowers and long stems is crossed with a rose plant that is heterozygous for red flowers and homozygous for short stems. What percentage of the offspring will exhibit red, long-stemmed flowers?

Let R represent red flowers and L represent long stems. The first plant is RRLL, so it passes on R and L to every offspring; the second is Rrll, so it passes on either R or r, but always l. Every offspring therefore has at least one R (red) and is Ll (long-stemmed). Thus, 100 percent will have red flowers and long stems, matching “100 percent.”

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