:dominance/recessive :heterozygotes: what happens? :1.dominant allele codes for a product;recessive does not :2.recessive allele produces less of a product :3.recessive allele produces functional enzyme that is masked. : :dominant relationships :1.lethal recessive organisms cannot survive :2.partial dominance/incomplete dominance - phenotype is blend or compromise :3.codominance: neither is recessive, equally dominant :4. multiple alleles: more than two alleles possible at a single locus : :gene interactions and modified mendelian ratios :9:3:3:1 occurs when two pairs of alleles act independently. at another locus a third gene can interact : :1.epitases: masking of a trait determined by one pair of genes by the actions of another pair of genes :2.pleiotropy: single gene can affect more than 1 characteristic :3.nature vs. nurture: environmental inteactions :4.incomplete penetrance may have abnormal genotype/normal phenotype :5.sex-limited and sex-influenced effects: a trait is only limited to or affects one gender more often :variable age of onset some traits do not appear until late in life :thomas hunt morgan : :polygenic-two or more genes control a single trait : :(original) central dogma of science: : dna -> rna -> protein : :beadle and tatum :experiments with neurospora : new central dogma: : dna -> rna -> polypeptide : :with retroviruses, the final dogma: : dna <-> rna -> polypeptide : : rna dna : ----- ----- : a a : c c : g g : u t : ribose deoxyribose :single strand double helix : : 5' gga 3' -> transcribe to :mRNA ccu -> translate to (ribs.) :tRNA gga : :mRNA: codon, tRNA: anticodon : :3 stages of protein synthesis :1. initiation: mature mrNA, ribosome, and tRNA carrying methionine (aug) form a complex. the iniator entes the P site leaving the A site open for incoming amino acids. :2.elongation: : a.tRNa with anticodon complementary to the 2nd codon (on mRNA) enters A site. : b.an enzyme joins the a.a. on the 1st tRNA to the a.a. on the 2nd tRNA. : c.the tRNA on the P site leaves, the tRNA in the A site moves to the P site and the next tRNa enters the empty A site in a process called translocation :d. ths repeats until a stop codon is reached (uaa, uag, uga) :3. termination: occurs when a releasing factor binds to the stop codon and causes the mRNA to leave the ribosome. :the new polypeptide chain is modified and/or joins with other chains to form mature protein. : :differences in prokaryote and eukaryote genomes : :prok:genes are in continuous sequence; several transcribed from same promoter :euk: genes transcribed one at a time and separated by stretches of noncoding dna called introns. :intron sequences are spliced out leaving the coding regions exons :bacteria lack the enzymes foor splicing eukaryotic rna. : :regulating gene expression :synthesis of proteins is regulated so that cells can respond to environmental conditions. bacteria synthesize the enzyme needed to break down the specific sugar present in the environment. amino acid synthesis is also energy efficient-bacteria produce amino acid-synthesizing enzymes only if amino acids are not available in the environment. bacteria can also produce spores in response to adverse conditions; this structural change requires controlled gene expression. :remember, protmoter=dna sequence that tells rna polymerase to start synthesizing rna. regulatory proteins can bind to dna to prevent transcription by blocking access to promote or by preventing progression of rna polymerase alon the gene. these are called repressors. : :NATURAL SELECTION AND POPULATION GENETICS : :1. gene pool: all genes of any population of a given time : evolution: change in allele frequencies in the gene pool :2. how gene pools change. : random changes -> cause evolution without natural selection : a. gene flow -> movement of alleles into or out of a population : (immigrantion/emigration) : b.genetic drift -> change in gene pool as a reult of chace : 1.) founder effect - small population branches off from a larger one. : ex. amish (6-finger) / afrikaaners in south america (descendants of 30 dutch settlers) : 2.) population bottleneck: population affected by natural disaster -> flood, volcano, eruption, tsunami (survivors may have rare alleles) : c. nonrandom mating: preferenceof particular phenotype : d. mutations: new mutations in gametes immediately change gene pool by substituting one allele for another (rare) effect is minimal in one generation; they are rare events but are the ultimate source of all genetic variation : :hardy-weinberg rules : 1.) pop is large enough to overcome chance events : 2.) mate choice is random : 3.) there is no mutation : 4.) no migration in or out of pop. : 5.) no selection pressure : :convergent evolution: :organisms that occupy similiar environments resemble one another - subjedted to similar selection pressures, have similiar adaptations; distantly related. : :divergent evolution: :isolated populations have different selective pressures acting on them - leads to different phenotypes : :MACROEVOLUTION: : :preadaptation - evolutionary plasticity is the ability of structures to serve alternative functions. ex. light, honeycomed bones may have first been fored for bipedal dinosaurs. increased surface area for "netting" insects. first flight have hae been extended hop (pred/prey situatin) or could have been a mating dance "glide" down from tree. : :paedomorphoses - sexually mature adults in one species keep structures that were in the juvenle form of ancestors. ex: salamanders - some retain gills as sexually mature adults : :developmental timing - brain size in humans and chimpanzees is different - brain growth stops later in human development : :heterochronic: changes in the timing or rate of development :homeotic: changes which alter placement of different body parts : :evolutionarytrends: : :1. gradualism: gradual change over time - gene pool compositio has constant, gradual rate of change. accumulated small changes. :2. punctuated equilibrium: faster tempo of evolution - new species from periphery of range of specis from rapid speciation. new species then outcompeted the old. sudden changes in environmental conditions caused population to change faster sometimes than at other times. : :between 3.5 and 4.0 billion years ago :have discovered crystallized minerals 4.1 bya (billion years ago) and sedimentary rock 3.8 bya - but no fossils :fig tree chert - 3.4 byo, this rock has fossilized prokaryotes :stromatolites - banded domes of sediment with spherical and filamentos prokaryotes; 3.5 bya. : :1. chemical evolution: life developed on earth from nonliving materials that became ordered into molecular aggregates, which eventually were capable of self-replication and metabolism. :spontaneous generation is not possible now, but the atmospheric conditins were different then. : *little to no oxygen : *lightening, volucaic activity, meteoritic bombardment, uv :radiation : :four stages to produce organisms: : -abiotic synthesis and accumulation of monomers (a.a. and nucleotides) : -joining of these monomers into polymers (proteins and nucleic acids) : -aggregation of abiotically produced molecules into : protobionts - droplets with chemical characteristics different than surroundings : -origin of heredity : :1953 - stanley miller and harold urey lab test - created the cnditions comparable to those of early earth. :produced a variety of amino acids and other organic compounds found in living organisms today! :the miller-urey model atmosphere: water, hydrogen gas, methane, ammonia - gases they believed revailed in ancient world. most important characteristic of this ancient atmosphere was rarity of oxygen gas. :2. production of organic polymers : clay has many charged sites on its particles - may have functioned as a lattice that brought monomers close togeth and assisted formation of polymers. :3. protobionts exhibit some properties associated with life such as metabolism and excitability. see p.491 fig. 24.5 :4. rna probably first! :some primitive mechanism may have existed for aligning amino acids along strand of rna that could replicate themselves. when rna is added to test-tube conaining monomers for making more rna, sequences 5-10 nucleotides long are copied - up to 40 nucleotides with zinc added as a catalyst, with less tha 1% error. ribozymes - biological catalyts for synthesis of new rna - so rna is autocatalytic. : : :----------------- :blood types: l : l : A A l :I I =A l : l : B B l :I I =B l : l : A B l :I I =AB l : l :ii=O l :-----------------