View
230
Download
2
Category
Preview:
Citation preview
16-1 Genetic Equilibrium
Chapter 16Population Genetics and
Speciation
Terms to Know
Population genetics – study of evolution from a genetic point of view
Microevolution – evolution at the genetic level
Bell Curve – most members of the population have similar traits; only a few are at the extremes– Can SHIFT over time!!!
Variations of Traits Within a Population
Causes of Variation1. Mutations
1. TAGATC -> TAAATC
2. Recombination (crossing-over and independent assortment)1. (during meiosis – see pic!)
– Random pairing of gametes– Which sex cells combine successfully
The Gene Pool Gene pool = the total genetic
information available in a population Allele Frequency = number of a
certain allele / total number of alleles in a population– Calculated by … # of allele A
total # of A and a
What is the allele frequency?
Half a population of four o clocks are red/ half are white.
What is the frequency of the r allele?– 0.50 or 50%
The Gene Pool
Phenotype Frequency = # of individuals with a phenotype / total # of individuals within the population
The Gene Pool Phenotype Frequency = # of individuals
with a phenotype / total # of individuals within the population
– # red flowers/ Total # of individuals
Hardy – Weinberg Genetic Equilibrium
Ideal hypothetical population that is not evolving (ie not changing over time)
5 criteria (must be met)1. No net mutations occur2. No one enters or leaves the population3. The population is large4. Individuals mate randomly5. Selection does not occur
Why might a population never be in HW genetic equilibrium???
Assignment
Pg 320 Q’s (1-5) – Answer in complete sentences! – Turn in when completed!
Read pg’s 321-325 and answer the Q’s given.
16-2 Disruption of Genetic Equilbrium
1. Mutation2. Gene flow – the process of genes
moving from one population to the next- Immigration- Emigration
3. Genetic Drift – allele frequencies in a population change usually because the population is small
4. Nonrandom mating – mate selection is influenced by geographic proximity, mates with similar traits, and sexual selection
5. Natural Selection – some members are more likely to survive and reproduce- stabilizing selection- disruptive selection- directional selection
Types of Selection
Stabilizing selection - individuals with average forms of a trait have the highest fitness– Ex. Large lizards
will be spotted by predators; small lizards can’t run fast enough to get away from predators
Types of Selection
Disruptive Selection – individuals with either extreme of the trait has the greatest fitness
– Ex. White moths on white trees cannot be seen; Dark moths on dark trees cannot be seen; medium colored moths will be seen on both trees (eaten by birds)
Types of Selection
Directional selection – more extreme form of a trait has the greatest fitness
– Ex. Anteaters with the longest tongues will get the most food
16-3 Formation of Species
The Concept of Species
Speciation – the process of species formation
Morphology – internal and external appearance of an organism
Species – morphologically similar and can interbreed to produce fully fertile offspring
Morphological vs Biological Species Concept
2 competing concepts (ideas) on how to determine different species– Morph = based solely on appearance
– Bio = based on who can reproduce with who successfully (not useful for extinct or asexual organisms)
– What do we use today? Mix of BOTH!!!
Isolation and Speciation
Geographic isolation – physical separation of members of a species– Ex. River dries up into several small
pools; fish diverged enough to be considered separate species
Reproductive Isolation – species become genetically isolated – Ex. The offspring of interbreeding
species may die early or may not be fertile
– Ex. Different mating times
Rates of Speciation
Gradualism – speciation occurs at a regular, gradual rate
Punctuated Equilibrium – sudden, rapid change then long periods of no change
Recommended