Variation and Evolution Why differences among a pop’n are good!

Review of Variation Order of DNA bases determines traits Changes can occur that can change individual Two possible ways changes occur: 1. M utations 2. G enetic Shuffling (Recombination)

Mutations Are random (cannot be predicted) Are random (cannot be predicted) Caused by radiation and chemicals Caused by radiation and chemicals To be passed on: To be passed on:  Single celled orgs (mitosis)  Sex cells of multicellular orgs

Mutations con’t… Most mutations harmful Most mutations harmful Some are beneficial (have adaptive value) Some are beneficial (have adaptive value)  These get passed on  These get passed on  Ex: polar bears prob didn’t always have black skin; mutation caused it and it was beneficial THIS IS MAIN SOURCE OF NEW VARIATION THIS IS MAIN SOURCE OF NEW VARIATION

Genetic Shuffling Sorting and recombination of genes = new combos of genes Sorting and recombination of genes = new combos of genes Think deck of cards: deck always the same but each hand is different Think deck of cards: deck always the same but each hand is different Sexual reprod. uses 2 decks so even more variation Sexual reprod. uses 2 decks so even more variation THIS IS MAIN SOURCE OF VARIATION WITHIN A SPECIES THIS IS MAIN SOURCE OF VARIATION WITHIN A SPECIES

Results of Genetic Variation 1. Structural changes 2. Functional changes 3. Behavioral changes

Structural Changes Result of orgs entire history Result of orgs entire history  Ex: polar bears vs other bears 1. Homologous Structures Evolution helps explain structural similarities Evolution helps explain structural similarities  Ex: (Arm structure) Humans, whales, birds and bats (RB p88) All have 1 long bone, 2 shorter ones, and 5 digits All have 1 long bone, 2 shorter ones, and 5 digits Tells us they all had a common ancestor Tells us they all had a common ancestor These are homologous structures! These are homologous structures!

Embryology

Structural Changes con’t 2. Vestigial Structures Structures that are present but no longer in use Structures that are present but no longer in use EX: Snakes contain tiny, non- functional leg bones which suggest it evolved from 4- legged lizards EX: Snakes contain tiny, non- functional leg bones which suggest it evolved from 4- legged lizards

Vestigial Structures (click link) Vestigial Structures (click link) Hind leg limbs in whales Pelvic bone in humans Appendix in humans

Functional Changes Molecular change Molecular change  EX: All muscles produce tiny electric current All muscles produce tiny electric current Eels have developed stronger current to help them find food and kill prey Eels have developed stronger current to help them find food and kill prey

Behavioral Changes Adaptive changes that increase reproductive success Adaptive changes that increase reproductive success EX: EX:  Fighting among males to “win” female  Rhythms of bird calls  Rates blinking in lightning bugs

Importance of Variation 1. Environment changes, orgs have to adapt 2. Without variation, species likely to become extinct 3. If diversity lost, difficult to recover 1. Endangered species have small pop’ns with little variation 2. If environment changes, cannot adapt

$2 SUMMARY OF THE IMPORTANCE OF VARIATION in EVOLUTION Each word is worth $.05 Each word is worth $.05 Freebies: Freebies:  a the as if and of in is it so by for to