Week 2 Notes
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This page Class Notes was uploaded by Chasia Notetaker on Saturday February 6, 2016. The Class Notes belongs to BIOL 12000 at Ithaca College taught by Nancy L Jacobson in Fall 2016. Since its upload, it has received 42 views. For similar materials see Fundamentals of Biology II: Ecology and E in Biology at Ithaca College.
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Date Created: 02/06/16
Week of February 1 2016 Evolution and Genetic Equilibrium General Evolutionchange over time eX of the universe of language Biological Evolutiongenetic change over time descent with modi cation the process of change that has transformed life on Earth from its earliest beginnings to the diversity of organisms living today Evolution as a Theory can explain a wide variety of observations adaptations by a population to local environment diversity of species some more similar than others wide array of fossils some from species that are not present now extremely well supported hypotheses continue to be generated and tested re ning the theory Review of Genetics Terms Genesheritable unit of information in DNA Alleles alternative versions of a geneusually encode slightly different versions of the same gene product Genotype the particular alleles of a gene carried by an individual Phenotype individual s observable traits Biological Evolution Occurs at Several Levels Microevolutiongenetic change within a population changes in allele frequencies in the population processes genetic drift natural and sexual selection and gene ow Speciationcan lead to formation of new species Macroevolution multiple speciation events leads to the formation of lineages of species which may show trends Evolution Depends on Variation within Population the source of all new alleles is mutation Mutationany change in the nucleotide sequence of DNA occur in all organisms occur randomly not because they are needed for mutation to affect a phenotype they must give rise to an altered gene product for mutation to be passed on to the next generation it must be in a gamete mutation can occur within the gene eX formed sicklecell allele mutation can occur in an already formed gene that regulated the affected gene the mutation may result in new copies of the gene eX gene duplication Mutation can Occur in Regulatory Sequences effects when the transcription of other genes is turned on or off different mutations occurred in different places Whole Genes can be Duplicated one gene becomes two with two genes one can still perform the old function while the other can mutate without harmful effects eventually the second may have a new function eX Opsins in primates The Case of Color Vision Evolution in Primates Dichromats VS Trichromats There are different ways to interpret light Chromatic vision Cone Cells cone cells in the retina of the eye allow light of different wavelengths to be interpreted as color in the brain Cone Cells have one type of opsin protein embedded in its membrane dichromats have two types of cone cells trichromats have three types of cone cells the type of opsin determines which wavelength of light causes a cone cell to send a signal to the brain the opsin protein makes the retinal molecule bound to it able to be changed when stimulated by particular wavelength Opsins SWS short wavelength sensitive MWSmedium wavelength sensitive LWSlong wavelength sensitive gt makes trichromats differ from dichromats opsin genesection of DNA on chromosome that codes for an opsin protein the LWS gene arose through gene duplication and gene mutation nucleotide substitution of the MWS gene on the Xchromosome unequal crossing over the difference between LWS and MWS is 30 nm three substitution mutations changed the properties of the opsin protein Population Genetics Gene pool all the alleles in the population Population all members of a species in a given location Genetic equilibrium no change of allele frequencies in a population For a Population to be in Genetic Equilibrium no mutation infinitely large population individuals with different phenotypes have an equal chance of survival and reproduction random breeding with regard to the phenotypes of the trait population is isolated no migration in or out if population is in genetic equilibrium allele frequencies aren t changing from one generation to the next How to tell if a Population is or has recently been Evolving or not look to see if allele frequencies are changing by generation if there is a long generation time observe the relationship between allele frequencies and genotype frequencies if population is in genetic equilibrium HardyWeinberg equations the rules of probability can be applied to inheritance EX probability of Bb producing a BB offspring Start with FAfrequency of dominant allelep Fafrequency of recessive alleleq Aa are the only alleles so pql gametes re ect allele frequencies of parental gene offspring re ect the allele frequencies of the gametes given the rules of probability p 22pgq 21 p 2 frequency of dominant genotype 2pq frequency of heterozygous genotype q 2 frequency of recessive genotype match genetic frequencies with actual genetic frequencies 17 gt Evolution Explain the Unity and Diversity of Life fossil record documents the fact that life has been evolving on Earth for billions of years differences of organisms re ect the evolutionary changes that occurred with their separate lineages during the history of their eXistence in Earth evolution accounts for life s dual nature of kinship and diversity Main Points from Darwin s Origin of Species First Species living today arose from a successor of ancestors that differed from them descent with modification Second Natural Selectionmechanism for evolution Observation 1 Individual Variation individuals in a population vary inherited from parents to offspring Observation 2 Overproduction of Offspringall species can produce more offspring than environment can sustain Competition for resources is inevitable many offspring fail to survive and reproduce Inference l Unequal reproductive success those with heritable traits best suited to the local environment are more likely to survive and reproduce than those that are less suited Inference 2 Accumulation of Favorable Traits over Time as a result of selective breeding the proportion of individuals in a population with advantageous traits grows l 6 gtGenes Control Phenotypic Traits through the EXpression of Proteins DNA inherited by an organism specifies traits by dictating the synthesis of proteins proteins are the link between genotype and phenotype gene dispatches information in the form of RNA Which programs protein synthesis Transcription synthesis of RNA under the direction of DNA Translation synthesis of protein under the direction of DNA Archibald Garrod suggested that genes dictate phenotype through enzymes inherited disease genotype re ects a person s inability to make a particular enzyme phenotype Beadle and Tatum s Hypothesis the function of a gene is to dictate the production of a polypeptide not accurate RNA transcribed is not always translated even though it has important functions many genes code for a set of polypeptides 1016 gt Mutations can Affect Genes silent mutations When an mRNA codon is changed but no change in protein product occurs because the new codon codes for the same protein as the previous codon missense mutationchanges one amino acid to another nonsense changes an amino acid codon into a stop codon frameshift mutationinvolves insertion or deletion of one or more nucleotides in a gene mutagenesis production of mutations mutagensphysical or chemical agents that cause mutations 138 gt Mutation and Sexual Reproduction Produce the Genetic Variation that makes Evolution Possible Genetic Variation not all variations in a population are heritable those impacted by environmental in uences cannot pass variations to offspring variations produced by polygenetic inheritance are determined by a single gene locus with different alleles producing distinct phenotypes eXplains variation in height from person to person Mutation only mutations in gametes can be passed to offspring and affect a population s genetic variability Sexual Reproduction neW eXisting alleles arise over generations due to crossing over independent orientation of homologous chromosomes at metaphase l of meiosis and random fertilization amp gt Alterations of Chromosome Structure can cause Birth defects and Cancer errors in meiosis or damaging agents such as radiation can cause a chromosome to break and can lead to deletion chromosomal fragments along with genes becomes detached duplicationWhen extra chromosomal fragment from deletion becomes an extra segment to its sister chromatic or a homologous chromosome 0 inversion When chromosomal fragment reattaches to the original chromosome in the reverse orientation 0 translocationWhen chromosomal fragment attaches to a nonhomologous chromosome deletions cause serious physical and mental problems cri du chat catcry is a developmental disability caused by a deletion in chromosome down syndrome is caused by only having a portion of chromosome 21 due to translocation CML chronic myelogenous leukemia is caused from the exchange of a very large portion of chromosome 22 with a small fragment of chromosome 9 causes cancer by activating a gene that leads to uncontrolled cell cycle progression 2910 gtThe Human Retina Contains Three Types of Photoreceptors Rods and Cones Cones stimulated by bright light and can distinguish color not much help with night vision Rodsextremely sensitive to light enable us to see in dim light but only in shades of gray relative number of rods and cones that an animal has is based on Whether the animal is more active in the day or night in humans rods are found in greater density at the outer edges of the retina completely absent at the fomea retina s center of focus cones are densest in the fomea aproximately 150000 per square millimeter each rod and cone consist of an array of membranous disks containing light absorbing visual pigments rods contain rhodopsin cones contain photopsins there are three types of cones each contains a different type of photopsin there are red blue and green cones colorblindness results from a de ciency in one or more types of cones How We See tips of rods and cones are embedded in the back of the retina light must pass through several relatively transparent layers of neurons before reaching the pigments of the rods and cones When rhodopsin and photopsin absorb light they change chemically change alters permeability of the cell s membrane resulting potential triggers a change in the release of neurotransmitters from synaptic terminals images are integrated in a maze of synapses Which helps sharpen image and increases contrast between dark and light areas action potentials carry the partly integrated information to the brain via synaptic nerve 3D perception results When visual input is integrated further in several processing centers of the cerebral cortex
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