Genetics and Mendel. Genes distinct packets that pass on hereditary information from generation to generation.

Transcription

1 Geneics and Mendel Geneics he sudy of herediy and variaion herediy he basic geneic blueprin of he parens is passed on o heir offspring. variaion he geneic difference beween parens and offspring Genes disinc packes ha pass on herediary informaion from generaion o generaion. may no be expressed for several generaions 1

2 17h and 18h cenuries conrolled experimens on inheriance were resriced quick breeding and prolific animals (ras/mice) were no accepable plan were no hough of as having sex religious resricions on experimens and beliefs, ye some experimenaion began 2

3 1800's hough ha some informaion in he blood of boh parens were mixed a concepion (hence he erm bloodline ) no based on careful scienific observaion and experimen 1860's: Two noions of inheriance: blending heory of inheriance seeds ha conrolled herediary rais were blended ogeher from generaion o generaion pangenesis herediary rais could be modified hroughou a person's lifeime Pangenesis heory of long giraffe neck 3

4 Gregor Mendel (mid cenury) Moravian Monk demonsraed he basis of herediy used science and mah o esablish paerns in how rais were inheried observed crosses in pea plans (Pisum saivum) The pea plan was ideal for hese sudies: self pollinaing so i was easy o conrol parenal crosses easily grown, maured quickly, producing many seeds show several pairs of conrasing rais 4

5 Conrolling he pollinaion process 5

6 Mendel's Experimens Phenoypes observable characerisics or rais (smooh or wrinkled peas, all or dwarf heigh, purple or whie flowers...) Viabiliy differen lines of plans could be expeced o produce approximaely he same number of plans for every 100 seeds planed P generaion (P for Parenal) cross beween pure breeding plans ha were differen for only one conrasing pair of rais Pure breeding Mendel began his experimens wih plans ha produced seeds ha grew ino plans idenical o he parens for several generaions 6

7 Hybrids resuling plans from he cross beween wo pure breeding plans wih only one conrasing pair of rais Pure breeding all plan Pure breeding dwarf plan The F 1 generaion are he resul of a all and a dwarf paren cross. Alhough hey are all all, hey have inheried conrasing heigh informaion from boh parens and so mus be a hybrid or combinaion. 7

8 Then he hybrid plans from he F 1 generaion were crossed. Pure breeding all plan Pure breeding dwarf plan F 1 Hybrid (all) F 1 Hybrid (all) The F 2 generaion ha resuled from crossing he F 1 hybrids revealed a 3:1 phenoypic raio all all all dwarf 8

9 The 3:1 raio resuls from which of he original P generaion paren rais is expressed or "urned on" Dominan Trai expressed rai, use uppercase leers (eg. T = Tall) Recessive Trai no expressed rai, use lowercase leers (eg. = Dwarf) Label he plans wih he rai hey are T expressing. Pure breeding all plan Pure breeding dwarf plan T T T F 1 Hybrid (all) F 1 Hybrid (all) T T T all all all dwarf 9

10 Mendel s Law of Segregaion Facors unis of inheriance (genes) for any given characerisic, here were several differen forms of hese genes called alleles Homologous Chromosomes Ex: Gene for plan heigh has wo differen alleles, a dominan all allele (T) and a recessive dwarf allele (). 10

11 Label he plans again, knowing ha each plan carries wo alleles for he heigh gene. T T T Pure breeding all plan T T Pure breeding dwarf plan F 1 Hybrid (all) F 1 Hybrid (all) TT T T all all all dwarf 11

12 To illusrae a cross more graphically, a Punne Square can be used. This works like a muliplicaion char. Consider he P generaion: Pure breeding dwarf plan () can only give a gamee Pure breeding all plan (TT) T T can only give a T gamee Only possible resul is a hybrid for boh alleles. Since T is dominan, all plans have a all phenoype. 12

13 The hybrids from he F 1 generaion are hen crossed: Hybrid (T) Hybrid (T) can give a T or a gamee can give a T or a gamee T T T T T T Any F 2 offsring wih he T allele has a all phenoype If no T allele is presen, he dwarf allele can be expressed 13

14 Each plan's phenoype was deermined by a pair of alleles ha could be idenical or differen. The allele expressed in he F 1 is dominan (all hybrids were all) The allele no expressed in he F 1 is recessive (he recessive dwarf allele could no be expressed unil he F 2 generaion) Law of Segregaion: Members of a pair of alleles for a given rai are segregaed (separaed) when gamees are formed. A heerozygous plan ha is T forms gamees ha are T and in equal numbers. The gamees are no a blend of he wo rais. Genoype gene makeup (he alleles an organism conains) Homozygous genoypes wih idenical alleles (example: TT or ) Heerozygous genoypes wih differen alleles (example: T) How'd you like hem peas? 14

15 Try a cross for round peas R and wrinkled peas, r. P R r R r Smooh Allele R Wrinkled Allele r F 1 R R r R R R r r R r r r F 2 Phenoypic Raio 15

16 Mendel s Law of Independen Assormen Consider more han one rai in a cross: Law of Independen Assormen: when wo or more pairs of characerisics are considered a one ime, each pair shows dominance and segregaion independenly of he oher. A plan ha is heerozygous for wo pairs of alleles, for example TRr, (for heigh and pea shape) can form four ypes of gamees: TR, Tr, R and r. These can be idenified using he FOIL mehod from expanding binomials from mah! T R r Dihybrid an individual who is heerozygous for wo rais: represened by he genoype AaBb for example. Dihybrid cross maing of wo individuals boh heerozygous for wo paricular rais (AaBb x AaBb). 16

17 gamees from F 1 dihybrids Try a dihybrid cross for heigh T pea shape Rr. T R T r R r F 2 Phenoypic raio T R Tr R r T T R R r T T R T R R T R r all round TRr x TRr T T R r r r T T T R r T r r all wrinkled T T R R r R T r r R r T R R R r R r r r dwarf round Tall Allele T Dwarf Allele Smooh Allele R Wrinkled Allele r dwarf wrinkled 17