Evolution: How species have changed over time. First a Perspective of Time. Those who influenced Darwin. Charles Darwin. Was a Naturalist – mostly observed organisms in their natural habitats rather than conducting experiments. Made most of his observations on the Galapagos Islands.
** Keep in mind this is BEFORE Mendel, Watson and Crick***
more individuals will have the “best” variation PLUS new mutations and combinations (with modification)
Directional Selection: One extreme or the other is “favored” and increases in frequency while midrange and other extreme decrease
Stabilizing Selection: Midrange is favored and increases in frequency while both extremes decrease.
Diversifying/disruptive Selection: Both extremes are favored and increase while midrange decreases.
– two organisms that can successfully reproduce and produce viable, fertile offspring
Cross between a Pug and a Beagle
- different breeds but SAME species
Both viable (obviously) and fertile
Cross between a Horse and Donkey
- different species
Viable but infertile
Half life of C14 – 5,730 years
Decay product is N14
If we look at the sample and determine the ratio of C14 to N14 we can get an idea of how much time has passed
Darwin did his work before Mendel and didn’t understand genes or how inheritance worked.
Thanks to Mendel we know how/why traits get passed from parent to offspring
But in turn will influence allele frequency.
Why aren’t all bad alleles eliminated??
Founding Population B
p2 = frequency of homozygous dominant
q2 = frequency of recessive genotype
2pq = frequency of heterozygote