Speciation topic- 2 Evidence for evolution

Homologous structures (homo- same)

Structures that are similar in different species, but are used differently. Show evidence of common ancestor. E.g. pentadactyl forelimb.

Pentadactyl forelimb

Limb made of 5 bones- similar structure in number animals, e.g human, leg, bird wing.

Analogous structures

Structures in different species that have similar function, but the structure are different. They evolved as an adaptation to same environment pressures, e.g. bird/insect wing.

Vestigial structures

Structures with no function in the organism now. E.g. Appendix in humans

Molecular Biology evidence

Look at nucleotide sequence of certain genes. If sequences have lots of differences- chances don’t share relatively recent common ancestor.

mtDNA (maternal) evidence

Mitochondria have their own DNA. This DNA does not undergo MEIOSIS- so no variation unless MUTATION happens. mtDNA comes from mother(ovum).

Y Chromosome analysis

Much smaller chromosome than ‘X’. Only tips exchanged (and alleles) during MEIOSIS. Result =95% Y chromosome stays same from father to son. Any changes due to MUTATION- these can be traced back to their origin.

Gradualism

Evolution happens at slow, steady rate. Will see the organisms in between with adaptive features(fossils)

Punctuated equilibrium

Short periods of evolutionary change mixed with periods of very little change. Happens if there are quick changes in environment or move to new habitat.

Convergent evolution

Evolution of similar phenotypes by species from different lineages

Divergent evolution

Evolution pattern where an ancestral species splits into 2 or more different species.

Sequential

Sometimes known as “linear” or “serial” evolution. Species change in stages over time, e.g. Homo Sapiens.

Co-evolution

Looks at effect to interacting species have on the evolution of each other, e.g. insects and flowering plants. Can make both vulnerable to extinction.

Adaptive radiation

Special type of DIVERGENT EVOLUTION. Looks at how large number new species evolve over short period from common ancestor. Populations adapt to fill new habitats and form new species.

CLINE

a gradual variation in the characteristics of a species or population over a geographical range.