Populations What is a population All the organisms

Populations What is a population? All the organisms of the same group or species, which live in a particular geographical area, and have the capability of interbreeding

Factors that Determine a Population’s Future: v population size – the number of individuals in a population v population density – the number of individuals that live in a given area v dispersion – the way the individuals of the population are arranged in space

For example; (1) Size - studies have shown that very small populations are among those most likely to become extinct. (2) Density - small populations within a given area tend to experience more inbreeding (breeding within relatives) which leads to a more genetically uniform population and an increase in homozygous recessive traits. (3) Dispersion - if individuals are randomly spaced, the location of each individual is determined by chance making reproduction rare.

Genetic Variation within a Population is due to: v Mutations v Crossing over in Meiosis v Recombination of Genes

Genetic Variation is stored in a population’s gene pool. v gene pool – the combined alleles of all of the individuals in a population v allele frequency- a measure of how common a certain allele is in the population EX: LL – long beak favorable trait Ll – long beak ll – short beak

The Hardy-Weinberg Principle: v states that the frequencies of alleles in a population do not change unless evolutionary forces act on the population. v the principle holds true for any population as long as the population is large enough that its members are not likely to mate with relatives and as long as evolutionary forces are not acting

Five Evolutionary Forces: natural selection – the frequency of an allele will increase or decrease depending on the allele’s effects on survival and reproduction; natural selection is one of the most powerful agents of genetic change. 2. gene mutations – any change in the DNA sequence; mutation rates in nature are very slow and not all mutations result in phenotypic changes 1.

gene flow – the movement of alleles into or out of a population; occurs because new individual (immigrants) add alleles to the population and departing individuals (emigrants) take alleles away 4. genetic drift – the frequency of an allele is greatly changed by a chance event such as a fire or landslide; occurs in small populations; the loss of even one individual from the population can have major effects on the allele’s frequency 3.

5. nonrandom mating– occurs when the individuals prefer to mate with others that live nearby or are of their own phenotype