Question

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.

Answer 1

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.

Answer 2

The first thing that could help you is that squares are male and circles are female, which means that C and D are incorrect.
Now, the sister has attached earlobes, so both parents must have the recessive allele along with the dominant, which means that the child has both recessive and dominant as well. This means that the correct answer is A. It is a male with at least one dominant allele.