Earlobes can be either attached or detached. the allele for attached earlobes is recessive (e), and the allele for detached earlobes is dominant (e). what must be true if a boy is born with attached earlobes? a. he has no recessive alleles. b. he has a homozygous genotype. c. he has a heterozygous genotype. d. he has one of each allele.

Option B, He has a homozygous genotype

Explanation:

A dominant allele is one which will overshadow the expression of recessive allele. Thus, when a dominant allele and recessive allele appears together in the genotype of offspring , only the trait associated with the dominant allele is expressed. Therefore , if a recessive allele trait is to be expressed , the offspring must have both the recessive allele

Let us see case here

A.Allele for attached earlobes is recessive (e)

B.  Allele for detached earlobes is dominant (E)

If offspring has EE genotype, then he/she would have detached earlobes

If offspring has Ee genotype, then also he/she would have detached earlobes as in heterogyzous genotype traits of dominant alleles are expressed.

If offspring has ee genotype, then only he/she would have attached earlobes

Genotype ee is a homozygous recessive genotype

The correct answer is option B.

Explanation:

The attached earlobes refer to a recessive trait, thus, it needs the existence of the two copies of the recessive allele in order to generate the particular trait. Hence, the boy must be homozygous recessive for the trait.  

However, it is possible only in three circumstances that the boy can possess attached earlobes. That is, when both the parents are heterozygous for the trait, when both the parents possess attached earlobes, or when one parent is homozygous recessive and the other is heterozygous for the same.  

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