Class Note for HCS 625 at OSU 05
Class Note for HCS 625 at OSU 05
Popular in Course
Popular in Department
This 3 page Class Notes was uploaded by an elite notetaker on Friday February 6, 2015. The Class Notes belongs to a course at Ohio State University taught by a professor in Fall. Since its upload, it has received 15 views.
Reviews for Class Note for HCS 625 at OSU 05
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 02/06/15
HampCS 625 Crop Breeding Period 04 April 6 2005 Modern plant breeding began when the emerging science of genetics was in its infancy Until the twentieth century various lines of genetic investigation cytology 7 cytogenetics evolution inheritance of characteristics were usually separate because so little was known about both transmitted characters and transmitted substances Scientist s at the turn of the century knew nothing about the genetic structure of populations and Darwin s theory had failed to give any explanation for the rudiments of hereditary transmission When Mendel s work was rediscovered at the turn of the century some viewed it as antagonistic to rather than complementary to the role of natural selection Reconciliation of Darwinian thought with Mendelian genetics was a challenge for some of the foremost geneticists of the day As the early 20th century progressed Darwin s ideas were gradually joined with the realizations made by Mendel ie particulate or physical inheritance of traits from the respective parents Researchers soon showed the relationship between the genotype and the phenotype in the inheritance of traits After Darwin described his initial theories of evolution he identified a fifth major premise Selection is the principal agent of change He acknowledged early plant and animal breeders in identifying selection as the chief directing agent in bringing about evolutionary change Many but not all plant and animal breeders acknowledged Darwin s principles It is not difficult to imagine how breeders could relate to concepts such as natural selection and adaptation when they themselves were engaged primarily in effecting selection pressure to develop better adapted strains of plants and animals The current scientif1c phase of plant breeding o The process started in the late nineteenth and early twentieth century 0 Darwinian and Mendelian principles became established as the framework within which evolutionary changes in living organisms occur The term NeoDarwinism wis adopted Formerly separate areas of research came together around the turn of the 20th century and gave rise to a general understanding of how species differentiated and became adapted to different environments The mechanics of just how genes fit into Darwin s evolutionary scheme were not readily apparent It had never been clear just what gave rise to the variations that provided the raw material for the evolutionary process There was also a dilemma in that most wild species are outcrossing so how could variation be maintained in a population or a species If populations were progressively diluted by outcrossing 7 how could they give rise to new species This problem was referred to as the swamping effect of crossing The solution lay in Mendel39s research character differences are not blended but persist During the early 20th century the concept of blending inheritance did not rest easily and the early Mendelists had a difficult time convincing others that the collective action of individual factors could be responsible for the observed patterns of continuous variation Enpenrnents by Johannsen helpeolto dlstmgulsh between the effects of the genotype and the envlronrnent tn the expresslon of eontanuously varymg tratts Hls enpenrnents eontnbuteol towarol the understandlng that eontanuously varymg tratts rnlght result from the presenee of rnultaple genetae factors eaeh responslble for some rneasurable olegree ofexpresslon ofthe quantltatave trart Johannsen found that wlth a general populau on of a selfrfemllzmg plant Phasealus beans seleetaon for a trart was effectlve ln shlftmg the average ofthe populatlon tn the dlrecnon of seleetaon ulzaoss rv yov See also http www olur ae ukstat Webhanimam htm But when seleetaon was slrnllarly appheolto the offspnng olenveol from selfrfemllzatlon of a smgle plant ltwas lnetreetlve ln changmg the average value othe eharaeter In short a populataon eonslsteol ofpure hnes or re selHng populatlons eventually wmd up as arnurture of dlsuncthomozygous farnllles Seleetlon appheolto arnureolpopulatlon sorts out pure hnes srnall large andlntermedwte but wlthln ahornogenous hne there ls no more genetae vanataon whlch ean responolto seleetaon He showeolthat the phenotype dlfferences between pure hnes asslgnable to a elass were hentable not that dlfferent genes eontrolleolthern per se He postulated that the dlfferences were clue to Mendellzlng factors that he terrneol genes To rnake concluslons about the lnhentanee ofgenes ltls neeessary to rnake a eross between parental genotypes dlsplaylng eontrastlng alleles and generate a segregatlng populataon e g F orprogemes eg F3 The problern wlth attnbutlng srnall dlfferences ln phenotypes to lnduldual genes ls that rt ls dlfflcult to elearly anol eonslstently seore srnall dlfferences ln quantltatave tratts Johannsen39s rnethoolology andthe factthathe ehose a seeollot thatwas lndeed eornpnseol of rnany pure 7 hnesquot was pararnount to the sueeess othe study It provlded awealth of clrcumstantla1 evldence quot Hls rnarket sarnple probably eonslsteol of abulk sarnple oflocal vaneues all ealleolthe sarne tlung by dlfferent farmers What rnlght happen lthe expenrnentwere eonolueteoltoolay7 Here are the enpenrnental proeeolures eourtesy of http www stat berkeley eduusersterryClassess2o0 l998Week4week4nod22 html Here ls what Johannsen deal He enpenrnenteol wth beans speclflcally Pnneess beans Phasealus vulgans mzmz Recall that llke peas beans are naturally selMertalrzrng He began hls senes ofexpenments ln 1900 by plantang anurnber of bean seeols from an 8 kg lot always perrnlttang selfrfemllzanon In 1901 he harvested287 plants from seleeteol seeols ofvery dlfferent 51235 and known welghts In 1902 he planteol 524 seeols from hls 1901 erop anol harvesteol 5494 seeols Eaeh of the 524 seeols onglnatedfrom one ofa set of 19 smgle beans whlch he oleslgnateol A B T He kept track of the weight in mg of the mother and the grandmother beans being Princesses all these beans are being viewed as female Finally he selected the smallest and largest beans seeds in each generation and planted these 19021907 For nice graphics and the data from the experiments see httpwwwbioloqieunihamburqdeboninee1313html As Mendel s principles were aligned with Darwin s theory and applied to populations and the source of variation mutation and the maintenance of variation allele frequency became both eXplainable and demonstrable Mutations and recombination were accepted as the sources of variation and gradual evolutionary changes in populations as a result of changes in gene frequency seemed quite logical It is also noteworthy that at the turn of the century transmission of genes on chromosomes was established Sutton and Boveri 190304 The Mendelian basis of continuous variation was recognized by researchers such as RA Fisher and a mathematical treatment of natural selection began The union of population genetics with natural selection generated a new view of the evolutionary process called Neo Darwinism By the end of the 1940s neoDarwinian ideas were almost universally accepted and some authors cited the development of a Modern Synthesis of evolution The leading features of modern evolutionary theory as stated by Simmonds and Smartt 1999 are as follows 0 Natural selection acts upon genetic variation and plant species are differentiated into subspecies ecotypes clines etc these populations often become separated geographically o Variability is maintained by heterozygosity supplemented by gene ow between populations 0 Heterozygosity polymorphic loci is adjusted upward or downwards by various cytological of genetical mechanisms A polymorphic locus is any locus that has more than one allele present within a population 0 Reproductive isolation between populations leads to speciation which generally develops gradually o Speciation is a continuous process It is not an endpoint or a discontinuous process 0 Adaptation is procured by successive gene substitutions in evolving populations leading to local differentiation and speciation I prefer the use of terms allele substitutions and allele frequency Different hereditary elements or factors 7 genes Alternative members of the elements alleles
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'