evolution and natural selection SL

content on evolution and natural selection in topics A4.1 and D4.1

define evolution (A4.1.1)

the process of cumulative change in the heritable characteristics of a population

convergent evolution

process by which unrelated organisms independently evolve similarities when adapting to similar environments

divergent evolution

accumulation of differences between closely related populations within a species, sometimes leading to speciation.

homologous structures

structures in different species that are similar because of common ancestry, but have become different in function

what evolution needs to occur

• variation within a population

• mechanism for inheritance of that variation (dna)

• a selection pressure leading to differential survival

why does evolution occur

• overpopulation leading to competition of limited resources

• environmental factors (biotic or abiotic) favouring survival of some individuals over others

• differential survival and reproduction

adaptive radiation

rapid evolution of an ancestral species in different lines to utilise the available ecological niches

natural selection

competition or environmental selection leads to some individuals dying, whereas others by virtue of their slight difference in phenotype survive to reproduce

trait

any feature of an organism

acquired trait

gained during an individual’s lifetime

genetic trait

can be passed down by genes to the next generation, present at birth

phenotype

observable characteristics of an individual resulting from its genotype

genotype

organisms genetic make up or allele combinations

allele frequency

number of times an allele occurs in a gene pool in comparison to other alleles for the same gene

biodiversity

variety of all life forms on earth

selection pressures

factors in the environment that are uneven in the effects they have on different individuals of a population

lamarkism

• inheritance of acquired characteristics

• modifications to phenotype during life of individual can be passed onto offspring

• lacks of a mechanism of inheritance

evidence for evolution

• comparative dna, rna and amino acid sequences

• selective breeding of domesticated animals and plants (domestication)

• homologous structures

• convergent evolution

• fossil record

molecular evidence for evolution

• dna has same structure across all organisms

• code for amino acid sequences using the same code

• rna and amino acid made from dna transcriptioin and translation so can be as evidence

selective breeding as evidence for evolution

• involves deliberate selection of offspring with particular trait and only using them to breed next generation (artificial selection)

homologous structures as evidence for evolution

• different function, same structure

• different selection pressure on the same structure adapts it for different functions

• different function makes the structure look different but have same underlying features which is evidence of their common ancestry

convergent evolution as evidence for evolution

• unrelated groups subjected to same selection pressures evolve similar phenotypes

• different underlying structure, same function

• analogous structures

speciation

formation of new and distinct species in the course of evolution

sympatric speciation

new species formed in same location due to isolating (temporal, behavioural) factors

allopatric speciation

geographical isolation prevent exchange of genetic material

abiotic factors

nonliving components of environment

biotic factors

living parts of an ecosystem

fitness

how well an individual is able to survive a given selection pressure and reproduce

hybridisation

interbreeding between two different species that leads to a new type of organism

prezygotic barrier to hybridisation

barriers that prevent breeding and fertilisation occurring

postzygotic

barriers that occurs after fertilisation