The pedigree chart below shows the individuals in a family who exhibit a certain trait. Based on the information in the chart, which of the following provides the best evidence that this is a recessive trait?
A diagram of a pedigree chart. At the top of the chart are two individuals, one indicated by a green circle and one by a green square. At the next level down, the green circle is paired with a black square and the green square is paired with a black circle. From the green circle, black square pairing, there are three offspring, a green circle, a green square, and a black square. From the green square, black circle pairing, there are eight offspring, three black circles and four black squares. Two of the black squares are identical twins. One of the black circles is paired with another black square. This pairing produced one green circle.
Key:
Circle—Female
Square—Male
Green—Exhibits trait"
Couple 3–4 in the 2nd generation produced children who do not show the trait.
Couple 1–2 in the 2nd generation produced children who do show the trait.
Couple 3–4 in the 2nd generation produced children who are identical twins.
Couple 1–2 in the 1st generation produced children who do show the trait.
