selection and speciation Flashcards
Explain why individuals within a population of a species may show a wide range of variation in phenotype
*genetic factors
*mutations- primary source of genetic variations
*crossing over between homologous chromosomes during meosis
*independent segragation of homologous chromosomes
*random fert of gametes during sexual reproduction
*environmental factors- like food availability, light int
What is evolution?
*change in allele frequency over many gens in a population
*occuring though natural selection
Whats natural selection
*process in which organisms become BETTER adapted to their environment to survive and reproduce, resulting in an increasing of the advantageous allele in the pop
What’s a population
*all organisms from SAME SPECIES living with one another in a habitat at the SAME TIME.
Describe factors that may drive natural selection
*prediation, disease and competition for the means of survival
*result in diff survival and reproduction
Explain the principles of natural selection in the evolution of populations
*Mutations- random gene mutations can result is new alleles
*Advanatage- due to x selction pressure, the new allele might benefit its processor bcs…- organism has a selective advantage
*Reproduction- possesors more likely to survive and have increased reproductive sucess
*Inheritance- advantageous allele is inherited by offsrping
*allele frequency- over many gens, allele increases in frequency in gene pool
Explain effects of stabilising selction
*organisms w alleles coding for modal variations of a trait have selctive advantage
*frequency of alleles coding for average variations of trait increase, those for extreme decreae
*so range is reduced
Explain the effects of directional selection
*organisms w alleles coding for ONE extre,e variations have SELECTIVE ADVANTAGE
*frequency of alleles coding for extreme variation increase, other extreme variation of trait decreases
Explain the effects of disruptive selection
*organisms with eirther extreme variation of a trait have selctive advantage
*frequency of alleles coding for BOTH extremes increase, others coding for AVERAGE varition decrease
*leads to speciation
Define speciation
*process of the creation of a new species
*when one original pop of same species become reproductivity isolated
Describe speciation (how new species arise from existing species)
*reproductive seperations of two populations
*can results in accumulation of diffs in their gene pools
*new spcies arise when these gen differences lead to an inability of members of the populations to interbreed and produce fert offsrpring
Describe allopatric speciation
*pop split due to geo isolation
*leads to reproductive isolation, seperating gene pools, by preventing interbreeding between pops
*random mutations cause gen variation within each pop
*diff selection pressures
*diff advantageous alleles are passed on in each pop
*allele frequencies between gene pool change over gens
*eventually diff pop cant interbreed to produce fert offspring
Describe sympatric speciation
*pop isnt geographically isolated
*mutations lead to reproductive isolation, sep gene pools by preventing interbreeding
*diff selection pressures act on each pop
*diff advantageous alles are passed on in each pop
*allele frequencies within each gene pool change over many gens
*eventually diff pops cant interbreed to produce fert offsrping
Explain genetic drift and its importance in small populations
*gen drift= a mechanism of evolution in which allele frequencies in a pop change over chance DUE TO CHANCE
*some alleles are passed onto offsrping more by chance
*regardless of selction pressures and whether alleles
give selctive advantage
*strongest effects in small pop w no interbreeding w other pops, as gene pool is small and chance has greater influence
*this can reduce gen diversity- some alleles have higher frequencies, others are lost
What is the bottle neck and founder effect
*population is sharply reduced in size (bottleneck effect)
* small, new colony forms from a main population (founder effect)
