1 1 1 BAS IC M E ND E LIA N A ND MOLEC U LA R GE NET ICS Ge neti c te rms y ou shoul d know a nd und erstand Gene Locus Allele Dominance Recessiveness Wild type Mutation Genotype Phenotype Homozygote Heterozygote Autosome Sex chromosome Hemizygous Pleiotropy Epistasis Haploid Diploid Nuclear DNA Mitochondrial DNA Chloroplast DNA Chromosome Me nd eli an ge net ics skill s you should have ma ste re d Basic Probability Sum rule product rule conditional probability 1 2 Monohybird 1 locus crosses Dihybrid 2 locus crosses Sex Linkage Fe ature s of t he G e netic C ode y ou shoul d know A G purines C T pyrimidines Genetic Code based on mRNA sequence Degeneracy wobble Replacement mutation nonsynonymous Silent mutation synonymous Frameshift mutations 1 Homologous chromosome Sister chromatid Tetrad Mitosis Meoisis Independent assortment Recombination Crossing over Transcription Translation 1 3 Fe ature s of Ge nom e St ructure you shoul d know Coding regions code for polypeptides proteins or tRNAs rRNAs Noncoding regions contain repetitive DNA sequences e g microsatellite loci Short Tandem Repeats longer repeats Alu is 300 bp long and copies occur 300 000 times in human genome 5 of human DNA Psedogenes are the result of duplications that have acquired a mutation producing a stop codon inside the coding region Introns transcribed but not translated portions of a gene Exons transcribed and translated portions of a gene 2 2 ME ND E L S POS TU LA TE S Basis of Mendel s success chose research organism well suited to his objectives experiments carefully designed collected large amounts of data used mathematical analysis to show that results were consistent with hypotheses Peas will sel f fe rtili ze unless they are cross pollinated by hand Must clip off anthers to prevent s el fi ng They re available in wide array of distinct t rue bree di ng ty pe s produce only progeny like themselves when they self Grew them for two years to insure true breeding Provided co nt ro l for hybridization Mendel obtained seeds for plants with distinct characteristics or p henoty pe s Bred true for flower color pod shape seed shape seed color etc True breeding types used as parents in hy brid iz ati on experiments 2 1 Me nd el s First Postulat e Genetic characters are controlled by unit factors that exist in pairs in individual organisms Pollen from round seeded plant used to pollinate wrinkled seeded plant vice versa P F1 Maternal parent wrinkled Reciprocal M o no hy bri d Crosses Paternal parent Maternal parent x all round round round selfed F2 2737 round F2 Ratio x all round Paternal parent wrinkled selfed 923 wrinkled 2750 round 2 99 1 920 wrink 3 1 Prevailing notion of heredity at the time was that the traits of parents bl ende d together to produce a hybrid with an intermediate phenotype But blending of characteristics was not observed in Mendel s experiments he saw p art ic ul ate inheritance Based on his experiments Gregor Mendel concluded that certain factors which we now call genes are passed from parents to their offspring Darwin s first postulate According to Mendel each organism has a pair of these factors that control the development of a specific trait When two organisms produce offspring each parent gives the offspring one of the factors from each pair In the offspring the two genes one from each parent act together 2 2 Me nd el s Sec ond Post ul ate D omi na nc e Rec essiv ene ss W he n t wo unli ke for a si ngl e c har acte r ar e pr es e nt i n a si ngl e i ndivi dual o ne unit fact o r i s d om ina nt t o t he ot her whic h i s s aid to be r ece s sive In the above monohybrid cross a recessive factor is covered up by a dominant factor in the F1 of a cross but it reappears in the F2 in a predictable proportion 1 4 The F1 plants all look like one of the parents round but retain the potential to produce wrinkle seeded offspring 3 Thus F1 plants are no longer true breeding they are hy bri d s Mendel invented terms do mi nant and re ce ss ive to describe this phenomenon T he tr ait that i s ma s ke d i n t he F1 i s rec es siv e The other is dominant According to the principle of dominance one gene in each pair may be stronger and prevent the other from being seen The recessive gene can however reappear in the F2 generation 2 3 Me nd el s T hi rd Post ulat e E q ual Se gre gati on During the formation of gametes the paired unit factors segregate randomly so that each gamete receives one or the other with equal likelihood Demonstrate using a Punnet Square Using modern notation capital letters denote dominant allele lower case letters denote recessive allele and the letter is often derived from the abnormal mutant form rather than from the normal wild type form F1 Male Sperm 1 2 W 1 2 w F1 Female Eggs 1 2 W 1 2 w 1 4 WW 1 4 Ww 1 4 Ww 1 4 ww Equal Segregation of genes into gametes Random union of gametes All these combinations equally likely 1 WW 2 Ww 1 ww 3 with dominant phenotype 1 recessive 2 4 Putti ng it all toget he r Parental phenotype Parental genotype Gametes F1 WW wrinkled x W ww diploid two copies of gene w haploid single copy of gene Ww F1 gametes F2 from selfed F1 2 5 round diploid W dominant to w W and w WW Ww ww Test C ross Since the W W and W w individuals all have the same phenotype how would you determine if you actually had the above genotypic ratio That is If an individual has the recessive phenotype wr i nkle d we know what it s genotype is ww But if it has the dominant phenotype r o und we don t know what the genotype is Individuals with a dominant phenotype can be either ho m oz y go us WW or het er o zy gous Ww in genotype 4 To determine genotype can cross an individual with the dominant phenotype to a plant with the recessive phenotype and recessive genotype WW x Gentoype Phenotype 2 6 ww Ww Ww all r o und x 1 2 W w 1 2 r o und ww 1 2 ww 1 2 wr ink The D ihy brid C ross and Me nd el s F ourt h Postulat e Ind ep e nd ent Se gre gat ion During gamete formation the segregation of one gene pair is independent of other gene pairs What if plants differ in 2 traits Mendel used the dihybrid cross in which 2 traits are …