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Unformatted text preview: today’s factoid • meat made from cultured animal 2ssue, and not whole animals could be in your future – e.g. in vitro pork is made from the ovaries of slaughtered pigs, which are fer2lized and the resul2ng embryos grown into 2ssue in a solu2on of nutrients http://scienceblogs.com/worldsfair/upload/2007/08/Meat%20without%20the %20animal.JPG • these methods may help solve a number of serious problems with growing animals for meat – ‐ineﬃciency of animal feed to meat conversion – ‐large "carbon footprint" of meat produc2on – ‐danger of human diseases that can be carried by livestock • e.g. swine ﬂu, mad cow disease see “in vitro meat” in Biology in the News on BB What is a genome? • The set of all genes plus all noncoding DNA • Noncoding DNA – Introns (in eukaryotes) – Sequences between genes – Repe22ve DNA • Some noncoding DNA may be “junk” but many func2ons of noncoding DNA are becoming known – e.g. Enhancers (see above) func2on in regula2on of gene expression Return to homology • Traits that two species share due to inheritance from a common ancestor • Homology of DNA and protein sequences is determined by aligning the sequences of diﬀerent species Various events can contribute to divergence of two species from their common ancestor Subs2tu2ons do not all occur at equal frequencies ‐various mathema2cal models are used to reconstruct evolu2onary history of DNA sequences A protein alignment (cytochrome C) Molecular evolu2on in nature is inferred from sequences • But we can witness it in the lab • AWer the experiment, bacterial strains can be completely sequenced • Morphologies evolved mul2ple 2mes • Diﬀerent nucleo2de subs2tu2ons led to same morphologies • These muta2ons also occurred in the shaken cultures but did not persist Synonymous vs. nonsynonymous subs2tu2ons • Syn >> Nonsyn • A pseudogene is a nonfunc2onal copy of a func2onal gene – Neutral: Neither advantageous nor disadvantageous “synonymous subs2tu2on” [aka muta2on at a “silent site”] “normal” gene (…ACTGGT…) “mutant” gene (…ACCGGT…) messenger RNA mRNA (…ACUGGU…) messenger RNA mRNA (…ACCGGU…) protein (…Thr Gly…) same protein (…Thr Gly…) function/phenotype same function/phenotype Some muta2ons alter the amino acid sequence, others do not The genetic code is degenerate; multiple codon sequences can encode the same amino acid. Evolu2on of neutral muta2ons • • • • • • Motoo Kimura, in 1968 proposed that most molecular varia2on in natural popula2ons is neutral Selec2on has no eﬀect on this varia2on; evolu2on is by gene2c dri: ‐ Recall “boclenecks” and other examples from previous lecture Muta2on rate: µ In diploids: # gene copies =2N (N= popula2on size) Average number of new muta2ons each genera2on: =µ•2N Probably that each new neutral muta2on will increase to 100% = its frequency =1/2N Overall frequency of new muta2ons increasing to 100% =µ•2N * 1/2N = µ , the muta2on rate (popula2on size doesn’t macer) • Larger popula2ons have more muta2ons than smaller popula2ons • Smaller popula2ons have fewer muta2ons but each one is more likely to go to 100% than in a larger popula2on Constancy of neutral muta2ons going to 100% (ﬁxa2on) leads to the idea of a molecular clock – Can use molecular data to es2mate the 2me two species have been diverging • • Selec2on at the molecular level • Recall two types of selec2on from previous lecture • Neutral evolu2on – Posi2ve (direc2onal) and stabilizing – Rate of synonymous subs2tu2on approx. = rate of nonsynonymous subs2tu2on • Stabilizing selec2on (selec2on for no change) • Posi2ve (direc2onal) selec2on (selec2on promotes change in amino acid sequence) – Rate of synonymous subs2tu2on << rate of nonsynonymous subs2tu2on – Rate of synonymous subs2tu2on > rate of nonsynonymous subs2tu2on Evolu2on of foregut fermenta2on • Posterior esophagous or stomach modiﬁed to hold bacteria, which digest plant macer (cellulose) via fermenta2on • Evolved independently in primates (langurs) and ruminants (cacle) • Also evolved independently in one lineage of birds (hoatzin) Molecular evolu2on of lysozyme in foregut fermenters • • Most animals, defensive enzyme (digests bacterial cell walls) In foregut fermenters, modiﬁca2ons of lysozyme have evolved – Enables some foregut bacteria to release nutrients, which are absorbed as food • 5 amino acid changes have evolved independently in both langurs and cacle • Some of these have also evolved in hoatzins Varia2on in gene number among species • Why? – Complexity – Other reasons? – What about coding vs. noncoding DNA? Varia2on in the amount of noncoding DNA • Why? – Diﬀering rates of loss of nonfunc2onal DNA – Rela2onship between DNA content and reproduc2ve rate ...
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This note was uploaded on 12/22/2009 for the course BIO 201 taught by Professor True during the Fall '08 term at SUNY Stony Brook.
- Fall '08