inheritance (condensed notes)

Chp14:Inheritance LearningOutcomesCandidatesshouldbeableto:(a)distinguishbetweenthetermsgeneandallele(b)explainthetermsdominant,recessive,codominant,homozygous,heterozygous,phenotypeandgenotype(c)predicttheresultsofsimplecrosseswithexpectedratiosof3:1and1:1,usingthetermshomozygous,heterozygous,F1generationandF2generation(d)explainwhyobservedratiosoftendifferfromexpectedratios,especiallywhentherearesmallnumbersofprogeny(e)usegeneticdiagramstosolveproblemsinvolvingmonohybridinheritance(f)explainco-dominanceandmultiplealleleswithreferencetotheinheritanceoftheABObloodgroupphenotypes(A,B,AB,O)andthegenealleles(IA,IBandIO)(g)describethedeterminationofsexinhumans–XXandXYchromosomes(h)describemutationasachangeinthesequenceofagenesuchasinsicklecellanaemia,orinthechromosomenumber,suchasthe47chromosomesintheconditionknownasDownsyndrome(i)nameionisingradiation(e.g.X-ray)andchemicalmutagensasfactorswhichmayincreasetherateofmutation(j)distinguishbetweencontinuousanddiscontinuousvariationandgiveexamplesofeach.

Chp14:Inheritance … VS … Gene:asequenceofDNAnucleotidesthatcontroltheformationofasinglepolypeptide.Aunitofinheritance. Allele:Differentformsofthesamegene.Theyoccupythesamerelativepositiononapairofhomologouschromosomes. Homozygous:having2identicalallelesofaparticulargene(egDD/dd) Heterozygous:having2differentallelesofaparticulargene(egDd) Dominant allele:theallelethatisexpressed(theoutwardappearance)- Canberepresentedbyauncapitalisedletter(Dd) Recessiveallele:theallelethatisunexpressed(notseenontheoutwardappearance)- Canberepresentedbyacapitalisedletter(Dd) Genotype:thecombinationofallelesforaparticulargene(howyour geneslook) Phenotype:Theexpressedtrait(theoutwardappearance/ Physicaltrait) Codominance:bothallelesexpressthemselvesintheheterozygote,whichhasaphenotypeintermediatebetweenthatofitspurebredparents. = eg:Redcow+whitecow=redandwhitecow Q:Whydoobservedratiosoftendifferfromexpectedratios,especiallywhentherearesmallnumbersofprogeny?ANS:Statistically,ratiosareinaccuratewhensamplenumbersaresmall.Also,duringfertilisation,thefusionofgametesisrandom,hencetheactualnumberofoffspringwillbeunlikelytomatchtheexpectedratioprecisely.(TBPg388)

Chp14:Inheritance DeterminingBloodTypes - TheallelesforbloodgroupsA,BandOaredesignatedI A , I B , I O respectively. - IAandIBaredominantoverIO(egpeoplewithallelesIOandIAwillhavebloodgroupB,peoplewithIOandIBwillhavebloodgroupB- I A , I B expresscodominanceandwillhavethebloodgroupAB. DeterminingSex - FemaleshaveXXchromosomes,maleshaveXY Mutation:achangeinthesequenceofagene(eginsicklecellanemia),orinthe chromosomenumberegpeoplewithDownsyndromehaveanextrachromosome,47in total) Factorsincreasingrateofmutation: - Ionisingradiation - Chemicalmutagens ContinuousvsDiscontinuousVariation

Chp14:Inheritance (additiveeffect-thecombinedeffectofmanygenes) (TBPg400) Sourcesof Geneticvariation:Meiosis,RandomFertilisation,Mutation ● Variationandcompetitionleadtodifferentialsurvivalof,andreproductionby,those organismsbestfittedtotheenvironment. 💪 ● Naturalselectionisapossiblemechanismforevolution,whichisagradualchangein theinheritablecharacteristicsofapopulationovertime. Anexampleofenvironmentalfactorsthatactasforcesofnaturalselection: - In1848,Englandexperiencedindustrialisationandmanytreesthatsurrounded factoriesproducingsmokewerecoveredinblackdust.Afterthis,thenumberof mothswithdarkcolouredwingsincreasedinthearea.Thiswasbecausetheycould camouflagebetterontheblackenedtreetrunksandcouldavoidgettingeaten,and hadmoretimetoreproduce.