Question

A man who is heterozygous for the dominant condition attached earlobe has a child with a woman who has an unattached earlobe. Their first child has an unattached earlobe. Which of the following mechanisms could explain the child's phenotype?

	A.	There is no explanation needed - this is normal Mendelian inheritance
	B.	Incomplete Penetrance
	C.	Variable expression
	D.	Incomplete dominance

Answer 1

Option A

Man = Ee (attached)

Woman = ee (unattached)

Ee × ee

Gametes	e
E	Ee attached
e	ee unattached

According to the given Four Square, a child can have either attached or attached earlobes. The probability of occurrence of both the types of hair loss is 50%. Therefore it follows a mendelian pattern of inheritance.

Incomplete dominance is the type of non mendelian inheritance in which dominant allele is in completely dominant over the recessive allele and therefore heterozygotes show intermediate phenotype.

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