The following pedigree shows the inheritance of attached earlobes (black symbols)and unattached earlobes (white symbol).Both alternative phenotypes are quite common in human populations. If the phenotypes are determined by alleles of one gene,then attached earlobes are inherited as:
A)an autosomal dominant trait.
B)an autosomal recessive trait.
C)a dominant trait that could be either autosomal or X-linked.
D)a recessive trait that could be either autosomal or X-linked.
E)an X-linked dominant trait.

Question

The following pedigree shows the inheritance of attached earlobes (black symbols)and unattached earlobes (white symbol).Both alternative phenotypes are quite common in human populations.  If the phenotypes are determined by alleles of one gene,then attached earlobes are inherited as:
A)an autosomal dominant trait. 
B)an autosomal recessive trait. 
C)a dominant trait that could be either autosomal or X-linked. 
D)a recessive trait that could be either autosomal or X-linked. 
E)an X-linked dominant trait.

Quizplus · Accepted Answer

If the phenotypes are determined by alleles of one gene and attached earlobes are more common than unattached earlobes, it suggests that attached earlobes are dominant. Since both males and females show the trait, it is most likely an autosomal dominant trait.

The Following Pedigree Shows the Inheritance of Attached Earlobes (Black