Question

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?

Answer 1

Let \(R,r\) denote the dominant and recessive alleles for flower color, respectively, and \(L,{l}\) denote the dominant and recessive alleles for stem length.

The dihybrid cross of \(RRLL\times Rrll\) has the following Punnett square:

Now, instead of doing all this work with the grid, you could have just made the observation that the alleles for one parent are all dominant, and so they will pass on to all the offspring. This means 100% of the next generation will exhibit red flowers and long stems.