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 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)

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