Biology 5C ~ Lecture 20 ~ The Evidence for evolution across deep time

all living organisms are

descended from a single common ancestor

homology

similarity in trait or gene due to common ancestry

-useful for examining shared ancestry

convergent evolution

similarity in trait or gene between organisms that do not share a recent common ancestor

-useful for observing selection pressure of similar environments

-results in homoplasy (traits that appear similar but are a result of convergent evolution)

evolution cannot create from scratch

-mutation works by changing a part or parts of sequences that already existed

-natural selection works on the variation that is present in the population

common ancestry is really important because

it shows us the ways that our body plans, our traits and our physiology are constrained due to the fact that we can't just produce any which organism we want with any traits we want

-shows us a lot about why an organism is the way they are

structural homology in limbs

all mammals share common ancestor

-underlying design is similar even though function or appearance is different
-have about 6000 species

structural homology in angiosperms

orchid flowers show diverse morphology but with the same basic elements (400,000 plant species)

descent with modification produces nested sets of shared traits

-this observation has predictable value (the more related you are to an organism, the more traits you'll share)

prediction:

extant organisms should share nested sets of novel traits

synapomorphy

a trait that is shared by the common ancestor and it's living descendants

more closely related organisms...

share more homologies

we use genes to build phylogenies

*use 'highly conserved' genes to estimate phylogenies (evolutionary relationships)

*more changes in genes, more distant relationship

Shared mutations: humans & chimpanzees share

a) map of the PMP-22 locus and flanking repeats on human chromosome 17

b) unequal crossing over that can occur as a result of misalignment during meiosis (can happen but not always)

c) genotypes resulting from fertilizations involving products of unequal crossing over

*shared flaws in organisms suggests common ancestry

pseudogenes

nonfunctional copies of normal genes that originate when processed mRNA is accidentally inserted into the genome

*can use to test hypothesis of common ancestry

exon

coding piece

intron

noncoding piece

common ancestry explains

why penguins have wings, humans have tailbones, snakes have limbs, and many other weird features of living organisms

life has been doing its thing for a long time

-several lines of evidence corroborate Earth's age (and life)

we know about the age that these things occurred for two reasons:

1) fossils - very helpful and we date them

2) we can track the genetic changes that occured in the same genes between these organisms and we can see how much time has passed through the amount of changes, and the amount of mutations that have accumulated between two different organisms

radiometric dating

radioactive isotopes decay at constant rates (unstable nuclei)

*an isotope that is decaying at a constant rate into some daughter product

different isotopes have...

different rates of decay (extremely consistent)

the age of earth and its living organisms

-earth formed roughly 4.5 billion years ago after the blast that formed our moon

-living organisms appear at least three billion years ago (maybe more)

quick review:

*homology is the similarity of features between living organisms due to common ancestry

*we observe both structural homology in traits and molecular homology in genomes

*common ancestry explains many peculiar features about extant organisms

*life began as a single cell three billion years ago and has diversified into all the organisms we see today