Download CHAPTER 16 POPULATION GENETICS AND SPECIATION Genetic

CHAPTER 16
POPULATION GENETICS AND SPECIATION
Genetic Equilibrium
1. Population genetics- the study of evolution from a genetic point of view. It is also
called microevolution.
a. Microevolution can be defined as a change in the collective genetic material
of a population.
b. A population is the smallest unit in which evolution can occur
c. Causes of variation within a population
i. Environmental factors
1. Amount of food
2. Quality of food
ii. Heredity
1. Variations in genotype caused by
a. Mutation- a random change in a gene that is passed to
offspring
b. Recombination- the reshuffling of genes. Independent
assortment and crossing over
c. The random pairing of gametes- everything is left up
to chance
2. The Gene Pool- the total genetic information available in a population
a. Phenotype frequency- is equal to the number of individuals with a particular
phenotype divided by the total number of individuals in the population.
i. Example: if you have 4 pink flowers and 4 red flowers the phenotype
frequency for pink flowers is 50% or 4 out of 8.
ii. Phenotype ratios can change drastically from generation to
generation based on the parent genotypes.
3. Hardy-Weinberg Genetic Equilibriuma. Hardy and Weinberg independently showed that genotypic frequencies in a
population tend to remain the same from generation to generation unless
acted upon by outside influences.
b. It is based on a set of assumption about an ideal hypothetical population that
is not evolving
Disruption of Genetic Equilibrium
1. Mutations can affect genetic equilibrium by producing totally new alleles for a trait.
Because natural selection operates only on genes that are expressed, it is very
slow to eliminate harmful recessive mutations.
2. Gene flow- The second requirement for genetic equilibrium is that size of the
population remains constant.
a) Immigration- is the movement of individuals into a population
b) Emigration- the movement of individuals out of a population
c) Gene flow is the process of genes moving from one population to
another.
Formation of Species
1. Isolation and Speciation
a. Speciation- the process of species formation
b. Species give rise to other species by being isolated from one another. There
are several different types of isolation
i. Geographic isolation-The physical separation of members of a
population.
Formation of a canyon from water runoff, drying climate in a
valley, bodies of water. In all cases the populations become
isolated from each other forming subpopulations eventually
making them incompatible for mating
a. Allopatric speciation happens when species arise as a
result of geographic isolation. Populations separated by
geographic barriers no longer experience gene flow
between them.
ii. Reproductive isolation- the inability of members of a population to
successfully interbreed with members of another population of the
same or a related species
a. Sympatric speciation-occurs when two subpopulations
become reproductively isolated within the same
geographic area.
i. Organisms in the same population competing
for the same resources could occupy slightly
different niches within the same ecosystem.
ii. This change could cause them to become
slightly different over time and possibly the
formation of a new species