Quantitative Inheritance - Pt.2. Chapter 8. Offspring-parent regression for height in humans (and why it’s called regression) (Fig. 8.11d). Assumptions of offpring-parent regression as an estimate of heritability.
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If heritability is high both monzygotic and dizygotic twins should resemble each other, but monzygotic twins should resemble each other more closely than dizygotic twins (because the former share all their genes, while the latter share only half their genes)
If heritability is low, then neither type of twin should show close resemblance
For striped snakes, the best survival strategy is straight-line escape.
For unstriped or spotted snakes, the best survival strategy is to reverse direction many times
From the figure at left, R = 9.7 - 8.9 = 0.8 mm
Average beak depth of the survivors of the drought was ~ 10.1 mm: S = 10.1 - 8.9 = 1.1 mm
Therefore, the realized heritability of beak length is:
h2 = R/S = 0.8/1.1 = 0.73
The slope of the regression line is about 0.5
Since this is offspring - single parent regression, h2 = twice the slope, or about 1.0
The slope of the line (the selection gradient) is about 0.13
This corresponds to a selection differential, S = 5%
(S = VPx selection gradient)
All of the difference in average plant height between these two genetically identical “populations” of Achillea is due to environmenal effects (Clausen, Keck and Heisey) (Fig. 8.26)Mather is in the foothills of the Sierra Nevada mountainsStanford is low altitude and near the Pacific coast
Populations of Achillea at different elevations are genetically different - but the direction of difference depends on the elevation of the “common garden” (Fig. 8.29)
Our conclusion about which population is genetically “programmed” to have plants with more stems will depend on where we chose to do the experiment.
This is an example of genotype by environment interaction