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)
author avatar
William Anderson (Schoolworkhelper Editorial Team)
William completed his Bachelor of Science and Master of Arts in 2013. He current serves as a lecturer, tutor and freelance writer. In his spare time, he enjoys reading, walking his dog and parasailing. Article last reviewed: 2022 | St. Rosemary Institution © 2010-2024 | Creative Commons 4.0

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