Heridity and evolution notes SA2 class10

Class 10 Heredity and Evolution – Gist of lessonGenetics :Branch of science that deals with Heredity and variation.Heredity :It means the transmission of features / characters/ traits from one generation to the next generation.Variation :The differences among the individuals of a species/population are called variations.Mendel and His Work on InheritanceGregor Johann Mendel started his experiments on plant breeding and hybridization. He proposed the laws of inheritance in living organisms. Mendel was known as Father of GeneticsPlant selected by Mendel :Pisum sativum(garden pea). Mendel used a number of contrasting characters for garden pea.Following are the seven pairs of contrasting characters in Garden Pea(TABLE OF CONTRASTING CHARACTERS. SEVEN PARTS)CHARACTERDOMINANT TRAITRECESSIVE TRAITFlower colourVioletWhiteFlower positionAxialTerminalSeed colourYellowGreenSeed shapeRoundWrinkledPod shapeInflatedConstrictedPod colourGreenYellowHeight of plantTallDwarf/ShortMendels Experiments :Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time)Monohybrid Cross :Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross. Example :Cross between a tall and a draft plant (short).Observations of Monohybrid Cross1. All F1 progeny were tall (no medium height plant (half way characteristic)2. F2 progeny ¼ were short, ¾ were tall3. Phenotypic ratio F2 – 3:1 (3 tall : 1 short)Genotypic ratio F2 – 1 : 2 :1 = TT : Tt : ttConclusions1. TT and Tt both are tall plants while tt is a short plant.2. A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.3. Characters/Traits like 'T' are called dominant trait (because it express itself) and ‘t’ are recessive trait (because it remains suppressed)Dihybrid Cross :A cross macle between two plants having two pairs of contrasting characters is called dihybrid cross.PARENT GENERATION--->ROUND GREEN SEEDS xWRINKLEDYELLOW SEEDSPhenotypic RatioObservations1. WhenRRyywas crossed with rrYY in F1 generation all wereRr Yy round and yellow seeds.2. Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants round yellow & wrinkled green) seeds plants in the ratio of 9:3:3:1Conclusions1. Round and yellow seeds areDOMINANTcharacters2. Occurrence of new phenotypic combinations show that genes for round and yellow seeds areinherited independentlyof each otherSEX DETERMINATION :Phenomenon of decision or determination of sex of an offspringFACTORS Responsible for Sex Determination1. Environmental : In some animals the temperature at which the fertilised eggs are kept decides the gender. eg. in Turtle 2.Genetic : In some animals like humans gender or individual is determined by a pair of chromosome called sex chromosome XX – Female and XY – MaleThis shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls. Thus sex ofchildren will be determined by what they inherit from their father, and not from their mother.EVOLUTIONEvaluation is the sequence of gradual changes which takes place in the primitive organisms, over millions of years, in which new species are produced.Situation-IGroup of red beetlesColour variation arises during reproductionAll beetles red except one that is greenOne beetle Green ReproductionCrows feed on red beetleProgeny beetles greenNo. of beetles reducesCrow could not feed on green beetles as they got camouflaged in green bushesNumber of green beetles increasesSituation 1 :Green beetles got the survival advantage or they were naturally selected as they were not visible in green bushes. This natural selection is exerted by crows resulting inadaptations in the beetles to fit better in their environmentSituation 2 :Blue beetles did not get survivals advantage. Elephant suddenly caused major havoc in beetle population otherwise their number would have been considerably large.From this we can conclude that accidents can change the frequency of some genes even if they do not get survival advantage: This is called genetic drift and it leads to variation.Characters or traits of an organism are controlled by the genesA Section of DNA (cellular)GeneProvides informationFor synthesis of ProteinsProteins controls a characterExample :Gene Tresponsible for synthesis of efficient enzyme (Protein)More productionof growth hormoneResults in Tall PlantsGene tresponsible for synthesis of less efficient enzymeLess productionof growth hormoneResults in short PlantsGenetic drift. It leads to diversity without any adaptationSITUATION-IIIGroup of red beetlesHabitat of beetles (bushes)Suffer from plant diseaseAverage weight of beetlesdecreases due to poor nourishmentNumber of beetles kept on reducingLater plant disease gets eliminatedNumber and average weight of the beetles increases againSituation 3 :No genetic change has occurred in the population of beetle. The population gets affected for a shortduration only due to environmental changes.ACQUIRED AND INHERITED TRAITSAcquired TraitsInherited Traits1. These are the traits which are developed in an individual due to special conditions1. These are the traits which are passed from one generation to the next.2. They cannot be transferred to the progeny2. They get transferred to the progeny.3. They cannot direct evolution eg. Low weight of starving beetles.3. They are helpful in evolution. eg. Colour of eyes and hairSPECIATIONMicro evolution : It is the evolution which is on a small scale. eg. change in body colour of beetles.The process by which new species develop from the existing species is known as speciation.Speciation : it is the process of formation of new species.Species : A group of similar individuals within a population that can interbreed and produce fertile offspring.Geneflow : It is exchange of genetic material by interbreedingbetween populations of same species or individualsWAYS BY WHICH SPECIATION TAKES PLACESpeciation takes place when variation is combined with geographical isolation.Gene flow :occurs between population that are partly but not completely separatedGENETIC DRIFTIt is the random change in the frequency of alleles (gene pair) in a population over successive generations.*Natural Selection :The process by which nature selects and consolidate those organisms which are more suitably adapted and possesses favorable variationsGenetic drift takes place due to(a) Severe changes in the DNA (b) Change in number of chromosomesEvolution and classificationBoth evolution and classification are interlinked.1. Classification of species is reflection of their evolutionary relationship.2. The more characteristic two species have in common the more closely they are related.3. The more closely they are related, the more recently they have a common ancestor.4. Similarities among organisms allow us to group them together and to study their characteristic.TRACING EVOLUTIONARY RELATIONSHIPS(Evidences of Evolution)I. Homologous Organs :(Morphological and anatomical evidences. These are the organs that have same basic structural plan and origin but different functions.Homologous organs provides evidence for evolution by telling us that they are derived from the same ancestor.Example :Forelimb of Horse(Running)Same basic structural but different functions perform.Winds of bat(flying) plan,Paw of a cat(walk/scratch/attack)II. Analogous Organs :These are the organs that have different origin and structural plan but same function example :Example :Analogous organs provide mechanism for evolution.Wings of bat elongated fingers with skin foldsWings of bird Feathery covering along the armDifferent basic structure, but perform similar function i.e., flightIII. Fossils :(Palaeontological evidences) : The remains and relics of dead organisms of the past.FOSSILS ARE PRESERVED TRACES OF LIVING ORGANISMSFossil Archaeopteryx possess features of reptiles as well as birds. This suggests that birds have evolved from reptiles.Examples of FossilsAMMONITE - Fossil-invertebrateTRILOBITE - Fossil-invertebrateKNIGHTIA - Fossil-fishRAJASAURUS - Fossil dinosaur skullAGE OF THE FOSSILSI. Deeper the fossil, older it is.II. Detecting the ratios of difference of the same element in the fossil material i.e.Radio-carbon dating[C-(14) dating)Evolution by stages :Evolution takes place in stages ie bit by bit over generations.I. Fitness advantageEvolution of EyesEvolution of complex organs is not sudden it occurs due to minor changes in DNA, however takes place bit by bit over generations.Flat worm has rudimentary eyesInsects have compound eyesenough to give fitness advantageHumans have binocular eyesII. Functional AdvantageEvolutions of feathers :Feathers provide insulation in cold weather but later they might become useful for flight.Example :Dinosaurs had feathers, but could not fly using feathers. Birds seem to have later adapted the feathers to flight.Evolution by Artificial Selection :Humans have been a powerful agent in modifying wild species to suit their own requirement throughout ages by using artificial selection. eg(i) From wild cabbage many varieties like broccoli, cauliflower, red cabbage, kale, cabbage and kohlrabi were obtained by artificial selection.(ii) Wheat (many varieties obtained due to artificial selection).Molecular PhylogenyÞIt is based on the idea that changes in DNA during reproduction are the basic events in evolutionÞOrganisms which are more distantly related will accumulategreater differences in their DNA