A4.1 Evolution and Speciation IB Bio- Evolution

Evolution- a change in the heritable characteristics of a population over

Lamarck- acquired traits when alive and these are beneficial for survival. And can be passed down to offspring evolution over time

  • not supported by genetics

  • acquired traits are not passed on to the offspring

Darwin- variation exists within a population. Nature selects individuals with the traits best adapted to survival and reproduction which are passed to the offspring- causing evolution over time

  • supported by genetics bc variation is present in a pop. bc of alleles

Evidence for Evolution

  • DNA, RNA, and protein sequences

    • same genes present in organisms→ evolution from a common ancestor

    • differences in base sequences of DNA and RNA are a result of mutations

    • Mutations accumulate gradually over long periods at a constant rate

    • Closely related species→ have similar gene and protein sequences w/differences due to mutations

  • Homologous structures

    • similar in structure but different functions.

    • common ancestor migrated to different areas and adapted to different environments

  • Selective breeding-

    • humans choosing plants or animals with desirable traits to breed together and produce offspring with desirable traits

Convergent Evolution- evolution of similar structures in species not related due to a recent common ancestor

Analogous Structures- common function but not a common structure- result

of convergent evolution ie wings

Speciation- formation of a new species through evolution

occurs as pre-existing species evolved into new species over time to the point where they cannot reproduce with each other.

Extinction- no living members of a species remaining

Pre-zygotic isolation vs. Post-zygotic isolation

  • pre-mating isolation occurs before fertilization

  • post-mating isolation occurs after fertilization

Geographical Isolation- often results in reproductive isolation

  • occurs when two populations are prevented from mating because of geographical features (rivers, mountains, etc.)

  • I.e. chimps and bonobos being separated by the Congo River. Chimps are nicer and the bonobos are meaner- speciation

HL Content

Sympatric Speciation- population divides into different species wile inhabiting the same habitat. aka behavioral or temporal

  • Behavioral Isolation- reproductive isolation due to behavior→ sympatric speciation ie. mating behavior in birds (different songs)

  • Temporal Isolation- organisms reproduce at different times i.e. Cicadas and their 13/17 yr life cycle underground

Allopatric Speciation- the physical separation of two populations of the same species - aka geographical isolation which leads to speciation

Adaptive Radiation- the evolution of a single ancestral species into several species. A result of divergent evolution- a single species moves to a variety of different niches and evolves different features due to different selective pressures. = more biodiversity

Hybrids- offspring of two different species

  • donkey+horse= mule

  • Sterile and are not considered a species

Hybridization is rare due to prezygotic and postzygotic barriers preventing the mixing of alleles between species.

Prezygotic barriers- prevent fertilization of egg and sperm

  • Behavioral Isolation

  • Temporal Isolation

  • Ecological Isolation- different habitats

  • Mechanical Isolation- physical differences prevent sexual intercourse

Post-zygotic barriers- in-viable or infertile offspring

  • Hybrid Inviability- offspring due no survive to become sexually mature adults

  • Hybrid Infertility- hybrids are not capable of producing fertile gametes

  • Hybrid breakdown- first generation of hybrids are capable of reproducing but the offspring cannot

Polyploidy- organisms with more than two sets of chromosomes in their cells. It is a result of non-disjunction, an error during meiosis

not polyploidy- haploid (one set of chromosomes) and diploid (two sets of chromosomes)

yes polyploidy- diploid+haploid= triploid 3n), diploid+dilploid= tetraploid (4n)

  • may produce immediate speciation because an organism is produced with a different number of chromosomes. (ie. bigger fruit in plants)

  • Polyploid plants with an even number of sets of chromosomes (4n, 6n, 8n …) are capable of reproducing sexually, as meiosis can occur with homologous pairs of chromosomes.

    Polyploid plants with an uneven number of sets of chromosomes (3n, 5n, 7n …) are sterile, as not all of the chromosomes can form homologous pairs during meiosis. Many of these plants can reproduce asexually.