Test your knowledge of conditional probability

4.	In certain isolated populations of humans in the New Jersey Pine Barrens (especially around Leeds Point, NJ) there is a autosomal dominant trait (A) in which affected individuals are born with the head of a horse, large wings, cloven hooves, horns and a tail. Individuals with this trait have been called various things including the Hoodle-Doodle Bird, "Wozzle Bug", the "Leeds Devil"and most famously, The New Jersey Devil. The recessive trait is a normal human.

	Geneticist Athin Schemata* has studied this extensively and she has shown that Devilism is an autosomal dominant trait with 10% penetrance in the homozygote and 5% penetrance in the heterozygote (which is why NJ Devils are so rare). Two New Jersey Devil’s are both known to be heterozygous (Aa). Their son Eddie is *phenotypically normal*; that is, Eddie may have the genotype AA, Aa or aa. What is the probability of Eddie having each genotype?

	Eddie grows up and marries a normal woman (Lucia Soprano) from North Jersey. This woman does a lot of genealogy and knows that there has never been a NJ Devil born in her family (i.e., her genotype is aa). Eddie and Lucia ask you to calculate the probability that their first child will be a New Jersey Devil. They also want to know the probability of having three normal children.

1.	Trait A is dominant to trait a and it shows 80% penetrance in the homozygous state and 50% penetrance in the heterozygous state. Two heterozygous individuals marry. What is the probability that their first child would show the a phenotype?
	Of those individuals with the a phenotype what proportion have the AA genotype, the Aa genotype and the aa genotype?

2.	The pole vault competition involves both running and accurate placement of the pole. Dead eye (accurate placement) is dominant to inaccurate. It is an autosomal trait. What is the probability that McJumper is heterozygous for dead eye? Dead eye, shows 60% penetrance in both the homozygous and heterozygous states. McJumper is an inaccurate male who is married to a homozygous inaccurate female. McJumper’s father was heterozygous for dead eye and his mother was homozygous inaccurate.
	a. What is the probability that McJumper is heterozygous for dead eye?
	b. What is the probability McJumper's first child will be a dead eye offspring?

3.	In Christmas Jelly fish, flashing lights are dominant to static lights. Flashing lights have 90% penetrance in the homozygote (AA) and 70% penetrance in the heterozygote (Aa). It is an autosomal trait. For each of the following different crosses give the distribution of phenotypes flashing lights and static lights.

Penetrance and Conditional Probability
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