LECTURE 7 : GENETICSIntroduction to Genetics and heredityGregor Mendel a rie! ioGenetic ter"inology #glossary$Monohyrid crosses%atterns o! inheritance&ihyrid crossesTest cross'eyond Mendelian Genetics inco"(lete do"inance Introduction to GeneticsGENETICS ranch o! iology that deals )ith heredity and *ariation o! organis"s+Chromosomes carry the hereditary in!or"ation #genes$,rrange"ent o! nucleotides in &N,&N, RN, %roteins Chro"oso"es #and genes$ occur in (airsHomologous ChromosomesNe) co"inations o! genes occur in se-ual re(roduction.ertili/ation !ro" t)o (arents Gregor 0ohann Mendel,ustrian Mon12 orn in )hat is no) C/ech Re(ulic in 3455Son o! (easant !ar"er2 studiedTheology and )as ordained(riest 6rder St+ ,ugustine+7ent to the uni*ersity o! 8ienna2 )here he studied otany and learned the Scienti!ic Method7or1ed )ith (ure lines o! (eas !or eight years%rior to Mendel2 heredity )as regarded as a 9lending9 (rocess and the o!!s(ring )ere essentially a 9dilution9o! the di!!erent (arental characteristics+ Mendel:s (easMendel loo1ed at se*en traits or characteristics o! (ea (lants: In 34;; he (ulished Experiments in Plant Hybridization2 #Versuche ber Pflanzen-Hybriden$in )hich he estalished his three %rinci(les o! Inheritance

7or1 )as largely ignored !or?@ years2 until 3ABB2 )hen ? inde(endent otanists redisco*ered Mendel:s )or1+ Mendel )as the !irst iologist to use Mathe"atics to e-(lain his results Cuantitati*ely+Mendel (redictedThe conce(t o! genesThat genes occur in (airsThat one gene o! each (air is(resent in the ga"etes Genetics ter"s you need to 1no):Gene a unit o! heredityD a section o! &N, seCuence encoding a single (roteinGenome the entire set o! genes in an organis"Alleles t)o genes that occu(y the sa"e (osition on ho"ologous chro"oso"es and that co*er the sa"e trait #li1e E!la*ors: o! a trait$+Locus a !i-ed location on a strand o! &N, )here a gene or one o! its alleles is located+ Homozygous ha*ing identical genes #one !ro" each (arent$ !or a (articular characteristic+Heterozygous ha*ing t)o di!!erent genes !or a (articular characteristic+Dominant the allele o! a gene that "as1s or su((resses the e-(ression o! an alternate alleleD the trait a((ears in the hetero/ygous condition+Recessive an allele that is "as1ed y a do"inant alleleD does not a((ear in the hetero/ygous condition2 only in ho"o/ygous+ Genotype the genetic "a1eu( o! an organis"shenotype the (hysical a((earance o! an organis" #Genoty(e F en*iron"ent$!onohy"ri# cross:a genetic cross in*ol*ing a single (air o! genes #one trait$D (arents di!!er y a single trait+ G %arental generation $% G .irst !ilial generationD o!!s(ring !ro" a genetic cross+ $& G Second !ilial generation o! a genetic cross Monohyrid cross%arents di!!er y a single trait+Crossing t)o (ea (lants that di!!er in ste" si/e2 one tall one shortT G allele !or Tallt G allele !or d)ar!TT G ho"o/ygous tall (lantt t G ho"o/ygous d)ar! (lantT T t t Monohyrid cross !or ste" length:T T t t #tall$ #d)ar!$% G (arentalstrue reeding2ho"o/ygous (lants:.3 generation is hetero/ygous:T t #all tall (lants$ %unnett sCuare, use!ul tool to do genetic crosses.or a "onohyrid cross2 you need a sCuare di*ided y !our>+Loo1s li1ea )indo)(ane>7e use the %unnett sCuareto (redict the genoty(es and (henoty(es o!the o!!s(ring+ Using a %unnett SCuareSTE%S: 3+ deter"ine the genoty(es o! the (arent organis"s 5+ )rite do)n your 9cross9 #"ating$ ?+ dra) a (HsCuare %arent genoty(es:TTandt tCrossT T t t %unnett sCuare@+ 'split' the letters o( the genotype (or each parent ) put them 'outsi#e' the p*s+uare I+ deter"ine the (ossile genoty(es o! the o!!s(ring y !illing in the (HsCuare ;+ su""ari/e results #genoty(es J (henoty(es o! o!!s(ring$T t T tT t T tT TttGenoty(es:3BBKT t%henoty(es:3BBK Tall (lantsT T t t Monohyrid cross: .5 generationI! you let the .3 generation sel!H!ertili/e2 the ne-t "onohyrid cross )ould e:T t T t#tall$#tall$T T T tT t t tT tT tGenoty(es:3 TTG Tall5 Tt G Tall3ttG d)ar! Genoty(ic ratioG 3:5:3%henoty(e:? Tall3 d)ar!%henoty(ic ratioG?:3 Secret o! the %unnett SCuareLey to the %unnett SCuare:&eter"ine the ga"etes o! each (arent>

pp p p

p p pp p p p pp p pI! you get IBK )hite2 IBK (ur(le !lo)ers2then the un1no)n (arent )as %p &ihyrid test crossMMI! you had a tall2 (ur(le (lant2 ho) )ould you 1no) )hat genoty(e it isMtt ppMM MM3+TT%%5+TT%p?+Tt%%@+Tt%p 'eyond Mendelian Genetics: Inco"(lete &o"inanceMendel )as luc1y=Traits he chose in the(ea (lant sho)ed u( *ery clearly>6ne allele )as do"inant o*er another2 so (henoty(es )ere easy to recogni/e+'ut so"eti"es (henoty(es arenot *ery o*ious> Inco"(lete &o"inanceSna(dragon !lo)ers co"e in "any colors+I! you cross a red sna(dragon #RR$ )ith a )hite sna(dragon #rr$Qou get %INL !lo)ers #Rr$=R RR rr rGenes sho) inco"(lete do"inance )hen the hetero/ygous (henoty(e is inter"ediate+ Inco"(lete do"inanceInco"(lete &o"inance 7hen .3 generation #all (in1 !lo)ers$ is sel! (ollinated2 the .5 generation is 3:5:3 red2 (in12 )hite RR R rR r r rRr Rr 7hat ha((ens i! you cross a (in1 )ith a )hiteMInco"(lete do"inance, (in1 )ith a redM Su""ary o! GeneticsChro"oso"es carry hereditary in!o #genes$Chro"oso"es #and genes$ occur in (airsNe) co"inations o! genes occur in se-ual re(roductionMonohyrid *s+ &ihyrid crossesMendel:s %rinci(les:&o"inance:one allele "as1s anotherSegregation: genes eco"e se(arated in ga"ete !or"ation Inde(endent ,ssort"ent: Me"ers o! one gene (air segregate inde(endently !ro" other gene (airs during ga"ete !or"ation Than1s=Re"e"er:Tui/ due on Thursday2 .eruary 3Ath+Re*ie) Session:.riday2 .eruary 5BT',+E-a" on Tuesday2 .eruary 5@th