Today s Outline. Inheritance. Darwin & Mendel near miss. Gregor Johann Mendel. Terms Punnett-square. Modern Synthesis

Transcription

1 Tody s Outline Inheritne Gregor Mendel Theory of segregtion Theory of independent ssortment Soures of vrition in popultions hromosoml sis of inheritne Humn genetis & ethis Gregor Johnn Mendel Gregor Johnn Mendel ( ) Tretise on Plnt Hyrids (1865) Drwin & Mendel ner miss Drwin ( ) Mendel ( ) Drwin Origin of speies (1859) Mendel - Tretise on Plnt Hyrids (1865) Modern Synthesis The unifition of Mendel s nd Drwin s theories y genetiists, pleontologists nd evolutionry iologists ( ). More thn 50 yers fter Drwin s nd Mendel s pulitions. Gene Lous llele Diploid Dominnt Reessive Homozygous Heterozygous Genotype phenotype rosses Terms Punnett-squre Segregtion Plieiotropy Vrition utosomes Linkge Duplition Inversion Deletion trnslotion

2 Mendel s Experiments The Grden Pe Plnt Self-pollinting True reeding (different lleles not normlly introdued) n e experimentlly rosspollinted Mendel s Experiments Trking Genertions Prentl genertion mtes to produe P First-genertion offspring F 1 mte to produe Seond-genertion offspring F 2 P F 1 X X F 1 ll purple flowers F 2 3:1 rtio of purple to white flowers

3 Mendel s hypothesis 1. Eh Prentl (P) pe plnt ontriuted 1 of 2 units (lleles) to the hyrid offspring. P X Homozygous 2. The purple flowered pe plnt hd two dominnt units while the white flower pe plnt hd two reessive units (oth re homozygous). F 1 Heterozygous 1 X Heterozygous Geneti Terms pir of homologous hromosomes gene lous F 2 3:1 rtio of purple to white flowers pir of lleles Three pirs of genes Mendel s Theory of Segregtion Diploid ells hve pirs of genes on homologous hromosomes. The two genes of eh pir re seprted from eh other during meiosis, so They end up in different gmetes. Homozygous dominnt prent hromosome duplition efore meiosis P Meiosis I Meiosis II Gmetes Homozygous reessive prent Punnett-Squre Method Monohyrid ross Homozygous Dominnt Homozygous Reessive F 1 Heterozygote

4 Phenotype & Genotype Punnett Squres of Test rosses Heterozygote Homozygotes Phenotype Purple flower White flower Genotype or Dihyrid ross Dihyrid ross rosses designed to evlute two hrteristis. For exmple: Mendel performed rosses etween purple flowered plnts nd long stems with white flowered nd short stem. TRUE- REEDING PRENTS: GMETES: purple flowers, tll x white flowers, dwrf F1 HYRID OFFSPRING: ll purple-flowered, tll Dihyrid Heterozygotes & Theory of Independent ssortment Independent ssortment How would the gmetes of these dihyrid heterozygotes ssort during meiosis? sed on his dihyrid rosses, Mendel proposed tht lleles will ssort independently from one nother. Of ourse, this is dependent on whether the genes re on the sme or different hromosomes. Metphse I Metphse II: OR If the genes re on different hromosomes they will ssort independently. If they re on the sme hromosome they will e linked nd ssort together. Gmetes: 1/4 1/4 1/4 1/4 lleles (4):

5 Inomplete Dominne Flower olor in Snpdrgons Pink-flowered plnt X Pink-flowered plnt (heterozygote) (heterozygote) White-, pink-, nd red-flowered plnts in 1:2:1 rtio odominne O lood Types lood Type O Genotype or O or O OO nd lleles re odominnt. O llele is reessive. odominne O lood Types ross Fther with lood Type? nd Mother with lood Type : Possile Outome No. 1 Possile Outome No. 2 odominne O lood Types ross Fther with lood Type? nd Mother with lood Type : Possile Outome No. 1 Possile Outome No. 2 O O odominne O lood Types Pleiotropy ross Fther with lood Type? nd Mother with lood Type : Possile Outome No. 1 Possile Outome No. 2 O O O pleiotropy - genes ffet severl different hrters in the sme individul. Exmple: sme gene ffets fur olor, ross-eyedness, nd voliztions in Simese ts

6 Pleiotropy Sikle-ell nemi H H H H S H S H S Epistsis: Intertions etween Gene Pirs F 1 : EE x ee Ee lk x Yellow E F 2 : Ee x Ee e E e E EE Ee EE Ee e Ee ee Ee ee E EE Ee EE Ee lk rown E melnin deposits e no melnin deposits e Ee ee Ee ee Some phenotypi hrters re determined y more thn one gene. Exmple: Humn skin olor Polygeni Trits Other Influenes on Gene Expression Environment uses vrition in how genotype is trnslted into phenotype. Muttion Produes new lleles. Size t mturity depends on environment Environmentl Effets on Phenotype Genotype 1: Low High pltyfish Genotype 2: Low High Genotype 3: Low High Smll Size t Mturity Lrge Light ot olor Wrm environment Drk ot olor old environment

7 Soures of Vrition Sexul reprodution llows offspring to hve oth different genotypes nd different phenotypes thn the prents. Sexul reprodution is n importnt soure of geneti vrition. Independent ssortment of hromosomes during meiosis produes gmetes with new omintions. hromosoml rossing-over during meiosis produes new omintions of linked genes in homologous hromosomes. The rndom fusion of gmetes from oth prents produes dditionl vrition. Sexul reprodution provides diversity for speies to survive environmentl hnge. hromosomes utosoml ll hromosomes exept sex hromosomes. Sme for men nd women. Sex hromosomes X nd Y hromosomes. They re nonidentil homologues. Women hve 2 X hromosomes Men hve one eh of X nd Y hromosomes. hromosoml ltertions rossover during prophse I of Meiosis. 1. rossover 2. Duplition 3. Inversion 4. Deletion 5. Trnslotion Fig. 11.2, p. 168 Duplition Duplition Gene sequene tht is repeted severl to hundreds of times norml hromosome Duplitions our in norml hromosomes My hve dptive dvntge one segment repeted Useful muttions my our in opy three repets

8 Inversion liner streth of DN is reversed within the hromosome Trnslotion piee of one hromosome eomes tthed to nother nonhomologous hromosome Most re reiprol Trnslotion Deletion hromosome nonhomologous hromosome Loss of some segment of hromosome Most re lethl or use serious disorder reiprol trnslotion neuploidy Individuls hve one extr or less hromosome (2n + 1 or 2n -1) Mjor use of humn reprodutive filure Most humn misrriges re neuploids Polyploidy Individuls hve three or more of eh type of hromosome (3n, 4n) ommon in flowering plnts Lethl for humns 99% die efore irth Neworns die soon fter irth

9 Nondisjuntion Down Syndrome Trisomy of hromosome 21 n + 1 n + 1 n -1 Mentl impirment nd vriety of dditionl defets n e deteted efore irth Risk of Down syndrome inreses drmtilly in mothers over ge 35 hromosome lignments t metphse I nondisjuntion t nphse I lignments t metphse II nphse II n -1 Turner Syndrome Inheritne of only one X (XO) 98% spontneously orted Survivors re short, infertile femles No funtionl ovries Seondry sexul trits redued My e treted with hormones, surgery Klinefelter Syndrome XXY ondition Results minly from nondisjuntion in mother (67%) Phenotype is tll mles Sterile or nerly so Feminized trits (sprse fil hir, somewht enlrged rests) Treted with testosterone injetions XYY ondition Tller thn verge mles Most otherwise phenotypilly norml Some mentlly impired One thought to e predisposed to riminl ehvior, ut studies now disredit