Micaela Clat

Chapter 20

Part I : Natural variation and 

microevolution

What constitutes variation?

Microevolution

What constitutes variation?

Microevolution

Microevolution

What constitutes variation?

Cape Floristic Kingdom  > 9,000 species

What constitutes variation?

Microevolution

What constitutes variation?

Cape peninsula > 2,256 species

Microevolution

Tafelberg – XX spp.

What constitutes variation?

Microevolution

Proteaceae ca. 1600 species

Microevolution

Microevolution

Microevolution

Microevolution

“But the much greater variability, as well as 

the greater frequency of monstrosities, 

under domestication or cultivation, than 

under nature, leads me to believe that 

deviations of structure are in some way 

due to the nature of the conditions of life, 

to which the parents and their more 

remote ancestors have been exposed 

during several generations.”

Phenotypic variation

Microevolution

Qualitative variation – discrete – no intermediates

When phenotypes are discrete – polymorphism 

Phenotypic variation

Microevolution

Quantitative variation – individuals differ in small incremental ways

‐‐ measurable and continuous

Microevolution

Microevolution

Genetic 

diversity

Phenotype

Environment

Microevolution

Genes and the environment can contribute to phenotypic variation

between individuals.

How do we distinguish between genetically controlled heritable variation 

and that controlled by the environment?

Phenotypic plasticity and heritable genetic traits

NOT heritable variation! Phenotypic plasticity

Heritable genetic variation

Uniform light

Heritable genetic variation

Uniform nutrients

Microevolution

Microevolution

Experimental research:

genetic of activity levels in mice

Microevolution

Chromosome

Gene

Allele (how many?)

Genotype – homozygotic vs. heterozygotic

Phenotype (characteristics)

Recessive vs. Dominant

Homozygotic gene...