1. Genes and Variation 16-1

2. Mutations and Gene Shuffling
What are the main sources of inheritable variation in a population?
(What is it that makes organisms different from one another?)
Mutations and Gene Shuffling

3. Mutations any change in a sequence of DNA
-may or may not affect phenotype
-may or may not affect "fitness"

4. Gene Shuffling
-this occurs during the production of gametes as chromosomes split and crossing over takes place
-in humans there is a possibility of 8.4 million different gene combinations (allele combinations)
-most differences are due to gene shuffling

5. What is a gene pool?
the combined genetic information of all the members of a particular population

6. What is relative frequency?
the number of times that an allele occurs in a gene pool compared with the number of times other alleles occur

7. What is a single-gene trait?
a trait controlled by a single gene that has two alleles
Like the following...

8. What is a Polygenic Trait?
A trait controlled by two or more genes and therefore more than two alleles
height
skin color
body shape

9. Evolution as Genetic Change 16-2

10. What is STABILIZING SELECTION?
WHEN INDIVIDUALS WITH THE AVERAGE FORM OF A TRAIT HAVE THE HIGHEST FITNESS
FOR EXAMPLE: THERE IS A POPULATION OF LIZARDS, SMALL MEDIUM LARGE
SMALL ARE NOT ABLE TO RUN FAST ENOUGH TO ESCAPE PREDATORS
LARGE ARE EASY TO SPOT SO THEY ARE CAPTURED AND EATEN BY PREDATORS
MEDIUM (AVERAGE) ARE SELECTED FOR AND ARE BEST SUITED TO THIS ENVIRONMENT

11. STABILIZING SELECTION

12. What is DIRECTIONAL SELECTION?
WHEN INDIVIDUALS THAT DISPLAY A MORE EXTREME FORM OF A TRAIT HAVE A GREATER FITNESS THAN AN INDIVIDUAL WITH AN AVERAGE FORM OF THAT TRAIT
FOR EXAMPLE: THERE IS A POPULATION OF ANTEATERS WITH SHORT MEDIUM LONG TONGUES
SHORT AND MEDIUM TONGUED CANNOT REACH INTO TERMITE NESTS TO EAT
LONG TONGUED CAN EFFECTIVELY REACH TERMITES INSIDE NEST

13. DIRECTIONAL SELECTION

14. What is DISRUPTIVE SELECTION?
WHEN INDIVIDUALS WITH EITHER EXTREME VARIATION OF A TRAIT HAVE A GREATER FITNESS THAN AN INDIVIDUAL WITH THE AVERAGE FORM OF THE TRAIT
FOR EXAMPLE: THERE IS A POPULATION OF SEASHELLS, COLORS VARY FROM WHITE TO DARK TAN
WHITE SHELLS ON WHITE ROCKS ARE HARD FOR BIRDS TO FIND
DARK TAN SHELLS ON DARK ROCKS ARE HARD FOR BIRDS TO FIND
COLORS INBETWEEN ARE EASILY SPOTTED AND EATEN

15. DISRUPTIVE SELECTION

16. What is genetic equilibrium?
the situation in which allele frequencies remain constant, meaning if they stay the same then the population WILL NOT evolve

17. 5 requirements for genetic equilibrium
Random Mating
Very large population
No movement into or out of the population
No mutations
No natural selection
If each condition holds true there will be no change

18. How is a new species formed?
a gene pool must be isolated from any others so they will only reproduce within that population until they cannot interbreed with any other population
How does a population become isolated?
-behavioral isolation:differences in courtship rituals
-geographic isolation:separated by geographic barriers
-temporal isolation:differences in reproducing times

20. What is GENE FLOW?
THE PROCESS OF GENES MOVING FROM ONE POPULATION TO ANOTHER
FOR EXAMPLE: THERE IS A POPULATION OF BABOONS, THE LESS DOMINANT MALES LEAVE THE GROUP AND GO TO ANOTHER POPULATION OF BABOONS

21. GENE FLOW

22. What is GENETIC DRIFT?
WHEN ALLELE FREQUENCIES IN A POPULATION CHANGE AS A RESULT OF RANDOM EVENTS
FOR EXAMPLE: A NEW DISEASE WIPES OUT A POPULATION OF SEALS, LEAVING ONLY A FEW LEFT (CAN CAUSE EXTINCTION DUE TO LESS VARIATION IN THE REMAINING POPULATION)

23. What is MUTATION?
A CHANGE IN DNA, WHICH CAN CREATE A NEW TRAIT IN A POPULATION, CAN HELP OR HURT
FOR EXAMPLE: A WHITE SQUIRREL (MUTATION) IS ABLE TO SURVIVE THE WINTER DUE TO SNOWFALL WHICH HELPS IT CAMOUFLAGE

24. MUTATION

25. WHAT IS NATURAL SELECTION?
AN ONGOING PROCESS IN NATURE IN WHICH SOME INDIVIDUALS IN A POPULATION ARE MORE LIKELY TO SURVIVE AND REPRODUCE
FOR EXAMPLE: BROWN RABBITS ARE MORE LIKELY TO SURVIVE IN THE DESERT THAN WHITE RABBITS BECAUSE OF THEIR COLOR, SO BROWN WILL PRODUCE OFFSPRING WITH THE SAME TRAITS (BROWN FUR)

26. NATURAL SELECTION IS NOT THIS!