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Equation 3 · Part 6 · Human Evolution Did Not Stop, and Medicine Is Now Steering It

fraction

qn+1=qn(1−sqn)1−sqn2q_{n+1} = \frac{q_n(1 - s q_n)}{1 - s q_n^2}
fraction

What this part means

Divide the expression above the line by the one below it.

Its job in the formula

The expression above the fraction bar is divided by the complete expression below it. The denominator must not be zero.

The passage around this formula

It is worth working through what that channel can and cannot do to a population’s allele frequencies, because the arithmetic is genuinely calculable and genuinely modest. Consider a recessive disease allele at population frequency q , and suppose that in some fraction of pregnancies where both parents are identified carriers, embryo testing prevents the birth of an affected (homozygous) child while parents still have the same number of children overall, drawn from the surviving unaffected and carrier embryos. The standard discrete-generation recursion for selection with coefficient s against a fully recessive genotype is: qn+1=qn(1−sqn)1−sqn2q_{n+1} = \frac{q_n(1 - s q_n)}{1 - s q_n^2}. Set s = 1 , the theoretical maximum in which…

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Learn the underlying idea

A fraction a/b means a divided by b. The top number is the numerator; the bottom number is the denominator, and it cannot be zero.

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Sources cited in the article section

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