Random change
- Key factors that can cause evolution:
- –Small populations are more variable to changes in allele frequencies
- -non-random mating opportunities result in only those “preferred” traits being passed onto future populations
- –new alleles may be created when mutations occur (changes the frequencies of new and original alleles)
- -migration causes changes in the relative abundance of alleles
- -natural selection takes place when individuals with certain alleles have greater reproductive success than others
- Ex: in population of 100 endangered frogs,1 frog that contained a particular allele and half of population got wiped out due to severe droughts
- 2 results possible for the frequency of this allele:
- This frog might be one of 50 that died (rare allele eliminated from gene pool)
- By some chance this frog survived and the allele frequency doubled
Genetic Drift
- change in the gene pool (total of all alleles in population) of a small population due to chance
- Two kinds of Genetic drift in nature:
- Bottleneck effect- Genetic drift(reduction of alleles in a population) resulting from a disaster that drastically reduces population size
- ex: earthquakes, volcanoes, floods, etc.
- Founder Effect-Genetic drift resulting from the colonization of a new location by a small number of individuals from a large original population.
- -allele frequency of new population is different from original population
- -very common with self-pollinations
- (ex: seed is transferred by a bird to a new location in which it germinates and forms a new population)
Gene Flow
- The gain or loss of alleles from a population by the movement of individuals
- Results of such event affects both populations
- Gene flow reduces differences between populations
- Mutations
- Mutations
- Changes in an organisms DNA that creates a new allele
- Only source of new genetic material and new alleles
- Since mutations are random events, there is a greater chance that their effects are:
- neutral (no effect on individuals reproductive success)or harmful (reduces individuals fitness) rather than beneficial ( inheritable changes that improve individual fitness)
Types of Mutations
- Point mutation-changes in single base-pairs along DNA molecule by either substitution, deletion or insertion
- -usually harmful and plays no major role in the evolution
- Gene duplication-when unequal crossing over takes place during meiosis resulting in an additional copy in one or more genes and reduction of genes on the other chromosomes
- Polyploidy-type of mutation that results in three or more sets of chromosomes in the offspring ( if a haploid gamete combines with a diploid gamete to make an individual that is triploidy)
- -provides individuals with immediate doubling of genetic information
- -organisms sometimes cane be tetraploid (4n) or even octoploid (8n)
