Download A population

Big Idea 1: The process of evolution drives the diversity and unity of life.
Enduring Understanding:
1A. Change in the genetic makeup of a population over time is Evolution.
Essential Knowledge: Natural selection is a major mechanism of evolution.
 According to Darwin’s theory of natural selection, individuals with more favorable
phenotypes are more likely to survive and produce more offspring. Thus, passing traits
to subsequent generations. Darwin’s idea was that resources are limited and that there
is competition for those resources.
 Natural selection is a major mechanism of evolution. Population is the smallest unit in
which evolution can occur. Individual cannot evolve.
 Population (group of individuals of the same species that share a gene pool
o Environment is always changing
o Acts upon the phenotype of the population
 Adaptation = a genetic variation favored by natural selection; characteristics that
become prevalent in a species because they help the members who have them survive
specific environmental pressures.
 Fitness is a quantitative measure of different reproductive success: how many fertile
offspring a member of a species contributes to the next generation compared to other
members.
Populations and Gene Pools:
 A population is a localized group of interbreeding individuals.
 Gene pool consists of all alleles for all of the genes for all the members of a population.
o Diverse gene pool good for long-term survival of a species. Genetic variations are
important!
 Allele frequency is frequency of allele in a population.
o Number of “A” alleles vs. number of “a” alleles
 If the frequencies of the two alleles DO NOT CHANGE from generation to generation, a
population is said to be in Hardy-Weinberg Equilibrium. (The population is not
undergoing a change in their gene pool.)
o Hardy-Weinberg equilibrium occurs if the following five conditions are met, and
describes the base situation in which a population is NOT EVOLVING.
 The population is large
 There is no migration of individuals into or out of the population
 There is no mutation of either of the alleles.
 Random mating occurs between members of the population.
 Natural selection is not acting on the allele.
 If all 5 conditions are met, the frequencies of the three possible genotypes of individuals
in the population for the two alleles are given by the equation;
p2 + 2pq + q2 = 1
 p2 is the frequency of the AA genotype (homozygous dominate)
 2pq is the frequency of the Aa genotype (heterozygous)
 P2 is the frequency of the aa genotype (homozygous recessive)
 To solve Hardy-Weinberg Problems follow these steps;
o Examine the information to determine what piece of information you have been
given about the population.
o Find out the value of p or q.
o Take the square root of q2 to find q
o Determine p by subtracting q from 1
o Determine p2 by multiplying p by itself
o Determine 2pq by multiplying (p x q)2.
o Check by adding up values.
 Allele frequency = p value and q value
 Individual people, organism, or individual phenotype = p2 +2pq +q2=1
Essential Knowledge: Natural selection acts on phenotypic variations in populations.
 Environments change and act as selective mechanisms on populations.
o Examples; Rock Pocket Mouse; Peppered Moth
 Phenotypic variations are not directed by the environment but occur through random
changes in the DNA and through new gene combinations.
 Some phenotypic variations significantly increases or decrease fitness of the organism
and the population.
o Example: Sickle Cell Anemia
 Humans impact variation in other species.
o Artificial selection.
o Overuse of antibiotics.