Factors that Cause Changes in the Gene Pool (Microevolution)

The conditions of the Hardy-Weinberg principle represent an ideal situation that rarely if ever occurs in WHAT

Natural populations

Processes taht do cause change in the gene pool include what

• Mutations

• Gene flow

• Non-random Mating

• Genetic drift

• Founder effect

• Bottleneck Effect

• Natural selection

Mutations

• A change that occurs in the WHAT of an individual

• If mutation is inheritable (occurs WHERE), it has the potential to AFFECT an entire WHAT

• May be neutral, positive or negative - Mutations that are beneficial provides WHAT for organisms with that mutation

• Initially diversifies the WHAT by introducing more WHAT

• A change that occurs in the DNA of an individual

• If mutation is inheritable (occurs GERM CELLS), it has the potential to AFFECT an entire GENE POOL

• May be neutral, positive or negative - Mutations that are beneficial provides a SELECTIVE ADVANTAGE for organisms with that mutation

• Initially diversifies the GENE POOL by introducing more VARIATION

Gene Flow

• The net movement of WHAT from one population to another due to the WHAT of individuals

• Increasing gene flow reduces WHAT among populations

MIGRATION

• The net movement of ALLELES from one population to another due to the MIGRATION of individuals

• Increasing gene flow reduces GENETIC DIFFERENCES among populations

Ex: A lone grey wolf may travel over 800 km in search of a new territory or breeding partner.  This brings new alleles into the gene pool of the nearby population increasing the genetic diversity of that population

Non-random mating

• Random mating which occurs when mating partners are WHAT chosen, much like drawing names out of a hat

• This rarely occurs in natural populations due to preferred WHAT and WHAT

• Random mating which occurs when mating partners are RANDOMLY chosen, much like drawing names out of a hat

• This rarely occurs in natural populations due to preferred PHENOTYPES and INBREEDING

Ex: Female sage grouse choose mates based on their physical characteristics; caribou compete for mates by sparring with their antlers ensuring only the strongest will mate; plants will self-fertilize which is an example of inbreeding

Genetic drift

• a change in WHAT due to chance events in a small WHAT population

BAD LUCK

• a change in ALLELE FREQUENCIES due to chance events in a small BREEDING population

Ex: In a population of roses where red is dominant to pink, due to random chance, none of the pink roses (aa) or roses heterozygous for pink (Aa) reproduced.  As a result, the pink allele was lost from the population in a very short amount of time.

Founder Effect

•  new populations are formed by only a few WHAT, or WHAT

• The founders will carry some but not all the WHAT in the original population limiting WHAT in the new colony

• Any rare alleles carried by founders may WHAT in frequency

• Occurs in WHAT populations

RED HAIR

•  new populations are formed by only a few INDIVIDUALS, or FOUNDERS

• The founders will carry some but not all the ALLELES in the original population limiting DIVERSITY in the new colony

• Any rare alleles carried by founders may INCREASE in frequency

• Occurs in HUMAN populations (ex: Saguenay river, Quebec)

Ex: A few birds migrating may be separated from their flock, and start their own colony.  

Bottleneck Effect

• gene pool change that results from a WHAT in population size

• May be caused by starvation, disease, human activities, natural disasters

PEPSI

• gene pool change that results from a RAPID DECREASE in population size

• May be caused by starvation, disease, human activities, natural disasters

Ex: Overhunting of elephant seals in 1890s reduced population to as few as 20.  Today the population has recovered however due to the bottleneck followed by genetic drift, their genetic diversity is very low

Natural selection

• individuals with WHAT that make them better suited to their environment are more likely to WHAT and WHAT which results in the WHAT of the organism to their environment

• Leads to WHAT

• The WHAT is what makes certain mutations beneficial, neutral or detrimental 

• Populations will evolve WHAT through time, but the rates of evolution between species will vary considerably depending on:

• Amount of WHAT in the population (↑↑)

• Intensity of the selection WHAT (↑↑) – if environment is changing little, very little WHAT, if changing a lot, extreme WHAT.  

• individuals with VARIATIONS that make them better suited to their environment are more likely to SURVIVE and REPRODUCE which results in the ADAPTATION of the organism to their environment

• Leads to EVOLUTION

• The ENVIRONMENT is what makes certain mutations beneficial, neutral or detrimental 

• Populations will evolve GRADUALLY through time, but the rates of evolution between species will vary considerably depending on

• Amount of VARIABILITY in the population (↑↑)

• Intensity of the selection PRESSURES (↑↑) – if environment is changing little, very little SELECTION PRESSURE, if changing a lot, extreme SELECTION PRESSURE.

Ex: peppered moth vs. melanic (black) moth in England – if there had not been variation within the species to begin with, the moths would most likely have been selected into extinction