Many large mammals, including humans and K selected individuals – Type I curve 

Many birds, small mammals, reptiles and some annual plants – Type II curve 

Many fish and marine invertebrates, r selected individuals - Type III curve

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#Unit 11. Evolution and Behavior

Phenotypic plasticity can be visualized with the reaction norm.

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#Unit 11. Evolution and Behavior

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#Unit 11. Evolution and Behavior

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#Unit 11. Evolution and Behavior

One is unequal crossing over, in which recombination happens between different positions on chromosomes that are misaligned during meiosis. 

Another is replication slippage, in which the DNA polymerase loses its place and copies a segment of chromosome twice.

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#Unit 11. Evolution and Behavior

A third way that gene duplicates arise is by retrotransposition.

Here the messenger RNA from a gene is reverse-transcribed to DNA, which is then integrated into the genome.

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#Unit 11. Evolution and Behavior

As a chromosome with a new gene duplicate spreads through a population, there is polymorphism in the number of copies of the gene that individuals carry. This situation, called copy number variation.