Consider the genetic cross for absent-mindedness, which is a dominant trait. All of the offspring from this cross will be absent-minded. If two parents that are absent-minded have offspring that are not, what MUST be the genotypes of the parents?

1 Answer
Oct 25, 2017

Both parents must heterozygous having one dominate gene for absent mindedness and one gene that codes for normal brain function.


In a punnett square cross for one trait there are four possibilities

AA, Aa, aA aa

Where A stands for the dominate gene for absent mindedness
Where a stands for the recessive gene for normal brain function

AA, Aa, aA all result in an offspring that is absent minded.

aa results is an offspring with normal brain function.

            A              a

A       AA            Aa

a aA aa

If one parent was homozogous for the trait all of the offspring would be absent mindedness

      A               A


a a A aA