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Homework 2 – BSCI370
1) What does the above figure illustrate about soapberry bug evolution? How do
natural selection, mutation, gene flow, and descent with modification each play a
role in this system?
There is natural variation in soapberry beak length.
Natural selection imposed by pod size drives increased (or decreased beak length),
mutation extends variation beyond the original standing variation, gene flow must be
restricted to allow divergent selection to drive evolution, and although both types of
soapberry bugs are descended from the same ancestors they have accumulated separate
modifications for their disparate habits.
Midoffspring vs. Midparent Height in Rhingrades
Midoffspring Height (cm)
Midparent Height (cm)
2) The above graph illustrates the relationship between height in parents and
offspring of Rhinogrades (a tropical mammal). What statement can be made
about the heritability of height? Can you say whether height is under genetic
control? Why is heritability important for Darwinian natural selection?
The best fit line has no discernible slope, and indicates the heritability in height is zero.
This does not mean that there are no genes for height. Heritability is a measure of the
amount of genetic variance, not inheritance. While there may be genes for height there
is no variance in those genes. The variance in the phenotype is all imposed by the
environment. This is important for selection because although selection can act on
phenotypic variance whether or not there is genetic variance, there will be no evolution
by natural selection if there is no genetic variance.