Ascertainment derivation
J.L. Marsh
Bio 137 B
© JLMarsh 1994
If we suspect that a disease is caused by a recessive mutation, the simple Mendelian
expection is that 25% of the children from matings between 2 carriers should be
affected.
However, the method of finding families to analyze introduces biases that
affect this expectation.
The following derivation permits a precise prediction to be made
that takes these biases into account.
If we find families to study by finding affected children and then gathering
data on the whole family, what proportion of offspring in these families will be
expected to be affected if it is a simple Mendelian trait?
To answer this, we
define a term (q') as the percent affected offspring expected given the bias of
complete truncate selection.
Previous workers have said that that percent q' =
q/[1-p
n
]
.
How can we prove that the # affected/total # persons in our sample is described
by
q' = q/[1-p
n
]
where n = family size rather than by the simple mendelian
prediction of 25% for a recessive?
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- Fall '09
- MARSH
- Multiplication, Mutation, families, J.L. Marsh Bio
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