Hey, consol, care to define evolution? Can you name off a few transitional fossils? Care to tell me why Lenski's research is relevant? Can you tell me the difference between homology and convergent evolution using examples? Do you know the differences between DNA and RNA? Do you even know what DNA and RNA stand for? Do you know why a chromosome having two centromeres is important?
I can't even think of a post you made where you presented a shred of evidence or demonstrated knowledge of biology.
Now that Kyrisch has spoilt it for consol, let me take the exam too
Evolution is change in the genetic composition of a population over time. That includes new mutations, selection and random drift.
A few transitional fossils? I'll come up with some that aren't mentioned in every second post here.
Archaeosperma, a primitive seed plant from the Devonian.
Westlothiana, a stem amniote first heralded as the first reptile.
Pistosaurus, a Triassic marine reptile transitional between nothosaurs and plesiosaurs.
The primitive feathers recently found in Early Cretaceous amber in France. And a
lot more.
Lenski's research - I'm thinking you mean the great
E. coli experiment that's been following the evolution of
E. coli lineages from a common ancestor for what, 20 years now? Most recently they have demonstrated both the evolution of a major novelty (the ability to digest citrate) and the role of historical contingency. That is, the bacteria which originally gave rise to Cit+ descendants were much more likely to yield them again - so they had some "potentiating" mutation that made the ability easier to evolve.
IIRC Lenski was also on the team that demonstrated the evolution of irreducible complexity in simulated organisms under simple selective pressures. The digital organism work also highlighted the fact that harmful mutations aren't necessarily bad - some of them were actually needed to evolve the target IC logical function in certain populations.
Homology is common ancestry of a feature in two organisms. Homologous features may be superficially very different. Convergent features are superficially similar but evolved independently. Perhaps my favourite example is our and squid's eyes. On the deepest level they may well be homologous. IIRC both use the
Pax6 gene to trigger eye development, as do other eyed creatures. This suggests that all eyes share a common ancestor (perhaps a bunch of light-sensitive cells on some ancient animal). However, even though human and squid eyes are superficially very similar, they have structural differences (eg. retina inverted in us and not in cephalopods) and, I've been told, the developmental pathways downstream from
Pax6 are also different. So on the level of details they are convergent.
RNA (ribonucleic acid) and DNA (deoxyRNA) are pretty similar in basic structure but the differences are important. First, deoxyribose has a hydrogen instead of an -OH group on carbon 2'. The extra -OH group makes RNA more reactive than DNA (it spontaneously chops itself up, for example). I'm sure I've been taught why DNA forms a stable double helix and RNA doesn't but I can't recall. Anyway, RNA tends to be single-stranded, but bits of the same strand can base-pair with each other, leading to complicated secondary structures.
Both nucleic acids feature complementary base-pairing: in DNA, the two pairs are guanine-cytosine and adenine-thymine. RNA has uracil instead of thymine (or rather: DNA has thymine instead of uracil, as RNA likely came first), and is less strict about what pairs with what than DNA. Uracil has a disadvantage: cytosine spontaneously converts to it. Of course a repair enzyme couldn't tell if a particular uracil is original or mutated from cytosine, so this error is unrepairable and increases the mutation rate of RNA (or uracil-DNA) compared to DNA.
With regards to function, DNA is an information storage molecule, and that's about it. RNA, on the other hand, performs in storage (many viral genomes), transmission (messenger RNA) and conversion (transfer RNA) of information, as well as in catalysis (ribosomal RNAs, self-splicing introns and other ribozymes). RNA interference is implicated in gene regulation (microRNAs) and defence against viruses.
And finally, a chromosome with two centromeres smacks of chromosome fusion. Normal chromosomes have only one centromere. In particular, the (defunct) second centromere of human chromosome 2 confirms a prediction of common descent: if humans (with 23 chromosome pairs) and other great apes (with 24 chromosome pairs) share a common ancestor then one of the human chromosomes must have formed by the fusion of two ape chromosomes (an ape can't just lose a chromosome and survive).
Do I pass?
