Observing Patterns in Inherited Traits. Chapter 10

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1 Observing Ptterns in Inherited Trits Chpter 10

2 10.1 Mendel, Pe Plnts, nd Inheritnce Ptterns By experimenting with pe plnts, Mendel ws the first to gther evidence of ptterns by which prents trnsmit genes to offspring

crpel stmen Grden pe flower, cut in hlf. Sperm form in pollen grins, which originte in mle florl prts (stmens). Eggs develop, fertiliztion tkes plce, nd seeds mture in femle florl prts (crpels).

3 crpel stmen Grden pe flower, cut in hlf. Sperm form in pollen grins, which originte in mle florl prts (stmens). Eggs develop, fertiliztion tkes plce, nd seeds mture in femle florl prts (crpels). b Pollen from plnt tht breeds true for purple flowers is brushed onto florl bud of plnt tht breeds true for white flowers. The white flower hd its stmens snipped off. This is one wy to ssure cross-fertiliztion of plnts. c Lter, seeds develop inside pods of the crossfertilized plnt. n embryo within ech seed develops into mture pe plnt. d Ech new plnt s flower color is indirect but observble evidence tht hereditry mteril hs been trnsmitted from the prent plnts. Fig. 10.3, p.154

4 Producing Hybrids Hybrids Offspring of cross between two individuls tht breed true for different forms of trit Ech inherits nonidenticl lleles for trit being studied

5 Homozygous dominnt prent Homozygous recessive prent (chromosomes duplicted before meiosis) meiosis I meiosis II (gmetes) (gmetes) fertiliztion produces heterozygous offspring Fig. 10.5, p.156

6 Heritble Units of Informtion Genes Heritble units of informtion bout trits Ech hs its own locus on the chromosome lleles Different moleculr forms of the sme gene Muttion Permnent chnge in gene s informtion

7 pir of homologous chromosomes, both unduplicted. In most species, one is inherited from femle prent nd its prtner from mle prent. b gene locus (plurl, loci), the loction for specific gene on chromosome. lleles re t corresponding loci on pir of homologous chromosomes c pir of lleles my be identicl or not. lleles re represented in the text by letters such s D or d. d Three pirs of genes (t three loci on this pir of homologous chromosomes); sme thing s three pirs of lleles. Fig. 10.4, p.155

8 Modern Genetic Terms Homozygous dominnt Hs two dominnt lleles for trit () Homozygous recessive Hs two recessive lleles () Heterozygote Hs two nonidenticl lleles ()

9 Modern Genetic Terms Dominnt llele my msk effect of recessive llele on the homologous chromosome Genotype n individul s lleles t ny or ll gene loci Phenotype n individul s observble trits

10 Key Concepts: MODERN GENETICS Gregor Mendel gthered the first indirect, experimentl evidence of the genetic bsis of inheritnce His meticulous work trcking trits in mny genertions of pe plnts gve him clues tht heritble trits re specified in units The units, distributed into gmetes in predictble ptterns, were lter identified s genes

11 10.2 Mendel s Theory of Segregtion Mendel s Theory of Segregtion: Diploid orgnisms hve pirs of genes, on pirs of homologous chromosomes Bsed on monohybrid experiments During meiosis Genes of ech pir seprte Ech gmete gets one or the other gene

12 Producing Hybrid Offspring Crossing two true-breeding prents of different genotypes yields hybrid offspring ll F 1 offspring re heterozygous for gene, nd cn be used in monohybrid experiments ll F 1 offspring of prentl cross x re

13 Monohybrid Cross Crosses between F 1 monohybrids resulted in these llelic combintions mong F 2 offspring Phenotype rtio 3:1 Evidence of dominnt nd recessive trits

Trit Studied Seed shpe Seed color Dominnt Form Recessive Form 5,474 round 1,850 wrinkled 6,022 yellow 2,001 green F2 Dominntto-Recessive Rtio 2.98:1 3.

14 Trit Studied Seed shpe Seed color Dominnt Form Recessive Form 5,474 round 1,850 wrinkled 6,022 yellow 2,001 green F2 Dominntto-Recessive Rtio 2.98:1 3.01:1 Pod shpe 882 inflted 299 wrinkled 2.95:1 Pod color 428 green 152 yellow 2.82:1 Flower color 705 purple 224 white 3.15:1 Flower position 651 long stem 207 t tip 3.14:1 Stem length 787 tll 277 dwrf 2.84:1 Fig. 10.6, p.156

15 mle gmetes femle gmetes From left to right, step-by-step construction of Punnett squre. Circles signify gmetes. stnds for dominnt llele nd for recessive llele t the sme gene locus. Offspring genotypes re indicted inside the squres. Fig. 10.7, p.157

16 mle gmetes femle gmetes Stepped rt Fig. 10-7, p.157

17 F 1 offspring True-breeding homozygous recessive prent plnt True-breeding homozygous dominnt prent plnt b Cross between two plnts tht breed true for different forms of trit. Fig. 10.7b, p.157

18 F2 offspring Heterozygous F 1 offspring Heterozygous F 1 offspring c Cross between heterozygous F1 offspring. Fig. 10.7c, p.157

19 Key Concepts: MONOHYBRID EXPERIMENTS Some experiments yielded evidence of gene segregtion When one chromosome seprtes from its homologous prtner during meiosis, the pirs of lleles on those chromosomes lso seprte nd end up in different gmetes

20 10.3 Mendel s Theory of Independent ssortment Mendel s Theory of Independent ssortment: Meiosis ssorts gene pirs of homologous chromosomes independently of gene pirs on ll other chromosomes Bsed on dihybrid experiments Pirs of homologous chromosomes lign rndomly t metphse I

21 One of two possible lignments The only other possible lignment Chromosome lignments t metphse I: B B b b b b B B b The resulting lignments t metphse II: B B b b b b B B c Possible combintions of lleles in gmetes: B B B b b b b b B B b B Fig. 10.8, p.158

22 Dihybrid Experiments Strt with cross between true-breeding heterozygous prents tht differ for lleles of two genes (BB x bb) ll F 1 offspring re heterozygous for both genes (Bb)

23 Mendel s Dihybrid Experiments Bb x Bb Phenotypes of the F 2 offspring of F 1 hybrids were close to 9:3:3:1 rtio 9 dominnt for both trits 3 dominnt for, recessive for b 3 dominnt for B, recessive for 1 recessive for both trits

Meiosis, gmete formtion in true-breeding prent plnts prent homozygous dominnt for purple flowers, tll stems Gmetes t fertiliztion prent homozygous recessive for white flowers, short stems

24 Meiosis, gmete formtion in true-breeding prent plnts prent homozygous dominnt for purple flowers, tll stems Gmetes t fertiliztion prent homozygous recessive for white flowers, short stems meiosis, gmete formtion Possible genotypes resulting from cross between two F 1 plnts: meiosis, gmete formtion ll F 1 plnts re Bb heterozygotes with purple flowers nd tll stems. Fig. 10.9, p.159

25 Key Concepts: DIHYBRID EXPERIMENTS Some experiments yielded evidence of independent ssortment During meiosis, the members of pir of homologous chromosomes re distributed into gmetes independently of ll other pirs

26 10.4 Beyond Simple Dominnce Other types of gene expression Codominnt lleles Incomplete dominnce Epistsis Pleiotropy

27 Genotypes: or BB or O B BO OO Phenotypes (Blood type): B B O Fig , p.160

28 Incomplete Dominnce n llele is not fully dominnt over its prtner on homologous chromosome Both re expressed Produces phenotype between the two homozygous conditions

29 homozygous prent (RR) x homozygous prent (rr) heterozygous F1 offspring (Rr) Cross two of the F1 plnts, nd the F2 offspring will show three phenotypes in 1:2:1 rtio: RR Rr Rr rr Fig , p.160

30 RRpp (rose comb) X rrpp (pe comb) F 1 of spring: RrPp (ll wlnut comb) F2 offspring: RrPp X RrPp RRPP, RRPp, RrPP, or RrPp RRpp or Rrpp rrpp or rrpp rrpp 9/16 wlnut 3/16 rose 3/16 pe 1/16 single comb Fig , p.161

31 EB Eb eb eb EB EEBB blck EEBb blck EeBB blck EeBb blck Eb EEBb blck EEbb chocolte EeBb blck Eebb chocolte eb EeBB blck EeBb blck eebb yellow eebb yellow eb EeBb blck Eebb chocolte eebb yellow eebb yellow Fig , p.161

32 Pleiotropy single gene my ffects two or more trits Exmple: Mrfn syndrome

33 10.5 Linkge Groups ll genes on the sme chromosome re prt of one linkge group Crossing over between homologous chromosomes disrupts gene linkges

34 Linkge Groups nd Meiosis During meiosis, genes reltively close together on chromosome tend to sty together Few crossover events occur between them Genes tht re reltively fr prt tend to ssort independently into gmetes Greter frequency of crossing over between them

35 Prentl genertion C C C c c c F 1 offspring ll Cc meiosis, gmete formtion Gmetes C c c C Most gmetes hve prentl genotypes smller number hve recombinnt genotypes Fig , p.162

36 10.6 Genes nd Environment Environmentl fctors my ffect gene expression in individuls Exmple: Temperture nd fur color

37 Elevtion nd Plnt Height

Height (centimeters) Height (centimeters) Height (centimeters) 60 0 Mture cutting t high elevtion (3,060 meters bove se level) 60 0 60

38 Height (centimeters) Height (centimeters) Height (centimeters) 60 0 Mture cutting t high elevtion (3,060 meters bove se level) b Mture cutting t mid-elevtion (1,400 meters bove se level) 0 c Mture cutting t low elevtion (30 meters bove se level) Fig , p.163

39 Predtion nd Body Form

40 10.7 Complex Vritions in Trits Polygenic Inheritnce When products of mny genes influence trit, individuls of popultion show rnge of continuous vrition for the trit

41 Continuous Vrition

42 Number of individuls with mesurble vlue for the trit This red grph line of the rnge of vrition for trit in popultion plots out s bell-shped curve. Such curves indicte continuous vrition in popultion. Rnge of vlues for the trit Fig , p.164

43 Vritions in Gene Expression Gene interctions nd environmentl fctors ffect most phenotypes Gene products control metbolic pthwys Muttions my lter or block pthwys

44 Key Concepts: VRITIONS ON MENDEL S THEME Not ll trits hve clerly dominnt or recessive forms One llele of pir my be fully or prtilly dominnt over its nonidenticl prtner, or codominnt with it

45 VRITIONS ON MENDEL S THEME (cont.) Two or more gene pirs often influence the sme trit, nd some single genes influence mny trits The environment lso influences vrition in gene expression

Genetics of heredity. October 10 Lecture notes Genetics of heredity

Genetics of heredity. October 10 Lecture notes Genetics of heredity October 10 Lecture notes Review: Meiosis, digrmmed on blckbord. Meiosis: The division of single nucleus (nd the cell tht contins it) into four dughter nuclei (nd cells tht contin them). The four dughter