In the family tree below, people with the recessive trait of attached earlobes
are shaded gray.
What must be true about the person labeled "A"?
O
A. It is a female with two dominant alleles.
O
B. It is a female with at least one dominant allele.
O
C. It is a male with at least one dominant allele.
O
D. It is a male with two dominant alleles.

B. It is a female with at least one dominant allele.

Explanation:

In pedigrees, a circle corresponds to a female, and a square to a male. The person labelled A is a circle, so must be a female.

Affected individuals are shaded grey. In this case, we are looking at the trait of attached earlobes, which is recessive. To have the trait you need two recessive alleles. This female is not affected, meaning she does not have two recessive alleles, one of her alleles must be the dominant allele.

That means, either she is heterozygous (has one dominant allele and one recessive allele) or homozygous dominant (two copies of the recessive allele)

i believe it would cause an increase of percipitation, though i could be wrong. so i would say b is the answer.