In a species of fern, there is a trait called branched dimorphism, in which the
ID: 12936 • Letter: I
Question
In a species of fern, there is a trait called branched dimorphism, in which the branches show two different patterns, as opposed to wildtype fern that only show one branching pattern. Two true-breeding parents, one single branching and the other with the dimorphic pattern, were crossed. All the F1 offspring displayed the single branching pattern. When the F1 plants were crossed, the F2 offspring were counted and it was found that there were 112 single branching offspring and 8 dimorphic branching offspring. How can you explain these results?Explanation / Answer
Let us consider the Single Branching as the dominant gene (AA), and Dimorphic branching as the recessive gene (aa).
Hence, when you breed AA X aa, the F1 generation would show the dominant phenotype, b/c their genotype is Aa (1 gene from each parent)
When the F1 generation breeds (Aa x Aa), 1/4 offsprings are (aa), 1/2 are (Aa) and 1/4 are (AA) gene offsprings. Since Aa and AA both represent the same phenotype, single branching, you can't tell which is which, but aa always shows dimorphism, and are easy to count.