To estimate the offspring phenotype from the cross of two parents selected from a base population you need several population parameters.
T = population mean
TF = mother phenotypic value
TM = fathers phenotypic value
T* = midparent value = (TF + TM)/2
h2 = narrow sense heritability estimate
To = predicted offspring value
Formula for predicted offspring value: To = T + h2(T* - T)
If TF = IQ of 120 and TM = IQ of 110, then
T* = (120 + 110)/2 = 115
How do the parents deviate from the population?
T*- T = 115- 100 = 15
How much of this deviation is heritable?
h2(T* - T) = 0.4(15) = 6
How will the offspring deviate from the population?
To = T + h2 (T* - T) = 100 + 6 = IQ of 106
This is the estimate of the offspring phenotype.