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"?
a. it is a male with at least one dominant allele.
b. it is a male with two dominant alleles.
c. it is a female with at least one dominant allele.
d. it is a female with two dominant alleles.

The correct answer is option (A) It is a male with at least one dominant allele.

Pedigrees are used in analyzing the pattern of inheritance of a particular trait in the family. A pedigree chart shows the presence or the absence of a trait within the family through many generations. A circle in the chart denotes a female and a square denotes a male. Complete shading of the circle or the square represents the affected individual.

Earlobes fall into two categories- free and attached. Attached earlobe is a recessive trait. The person labelled 'A" in the pedigree chart is a male with atleast one dominant allele.  It is because the sister has attached ear lobes and has inherited both her recessive alleles, each from her parents. Therefore the parents have a dominant free lobe allele and a recessive attached lobe allele. So, the unaffected son has the same genetic compositon or the genotype.  

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