1/11/15$1$Mechanisms$$of$Evolu4on$How$do$we$know$if$a$popula4on$is$evolving?$Microevolu*on:--a$change$in$the$rela4ve$frequencies$of$alleles$in$a$gene$pool$over$4me$1/11/15$2$Review$Mitosis$&$Meiosis$Mitosis: • Results in 2 diploid cells • Identical to parent cell Meiosis: • Results in 4 haploid daughter cells. • Each daughter cell contains half genetic material as the parent cell. • Each daughter cell is genetically unique. Law$of$Independent$Assortment$makes a copy of the cell *review LS21/11/15$3$Humans$can$produce$$8.4$million$different$gametes$$=$7$x$1013$combina4ons$possible$for$every$couple!$Independent$assortment$$!$Gamete$Diversity$PunneT$Square$B- b-B- BB$ Bb$b- Bb$ bb$Paternal$Maternal$(0.5)$(0.5)$(0.5)$(0.5)$(0.5)$(0.5)$(0.5)$(0.5)$• Dominant$• Recessive$• Homozygous$• Heterozygous$• Probability$of$genotype$of$the$offspring$two diff alleles1/11/15$4$HardyZWeinberg$equilibrium$Allele$frequencies:$$p-+-q-=-1-Genotype$frequencies:$$p2-+-2pq-+-q2-=-1-If$HardyZWeinberg$condi4ons$are$met,$we$can$compute$the$frequencies$of$the$three$possible$genotypes:$$Alleles$ $ $$$A$$$and$$$a$$Genotypes $$$AA$$$$Aa$$$$aa#$Genotype $$$p2$$$$$2pq $q2$Frequencies$Relationship allows translation between allele frequencies and genotype frequencies. has to equal 1 or 100%1/11/15$5$Allele$frequencies:$p$+$q$=$1$$p$=$B$=$0.6$q$=$b$=$0.4$$0.6$+$0.4$=$1$B- b-B- BB$ Bb$b- Bb$ bb$Paternal$Maternal$(0.6)$(0.4)$(0.4)$(0.4)$(0.6)$(0.4)$(0.6)$(0.6)$(p)$(p)$(p)$(q)$(p)$(q)$(q)$(q)$Genotype$frequencies:$ $$p2$+$2pq$+$q2$=$1$$(0.6)2$+$2(0.6*0.4)$+$(0.4)2$=$1$HardyZWeinberg$equilibrium$=$popula4on$is$not$evolving$Assump4ons:$1. No$Natural$Selec4on$2. No$gene$flow$3. No$muta4ons$4. No$gene4c$drid$5. Random$ma4ng$!$allele$frequencies$remain$the$same$from$one$genera4on$to$the$next$1/11/15$6$HardyZWeinberg$equilibrium$1.-No-Natural-Selec*on:--There$can$be$no$differences$in$survival$and$reproduc4ve$success$of$individuals$If$a$phenotype$is$successful,$all$alleles$for$that$individual$will$be$selected$for,$and$the$frequency$of$the$alleles$will$change.$$Alleles$can$become$fixed$in$the$popula4on$–$frequency$of$a$fixed$allele$is$1$–$or$eliminated.$$Balancing-Selec*on:---two$or$more$alleles$are$maintained$in$the$popula4on.$Some$deleterious$alleles$remain$in$the$popula4on.$$Heterozygote-advantage-$Example:$Sickle$Cell$$AA$=$normal$red$blood$cells$$SS$=$all$sickled$cells$$SA$=$some$sickled$cells$$$What$is$the$adap4ve$advantage$of$maintaining$the$S$allele?$might be harmful1/11/15$7$Some$deleterious$alleles$remain$in$the$popula4on.$$Heterozygote-advantage-$Example:$Sickle$Cell$SA$individuals$(w/$some$sickled$cells)$have$an$advantage$!$Protec4on$against$malaria$Therefore,$both$S$and$A$alleles$are$maintained$in$the$popula4on.$Plasmodium#spp.$$Malaria$parasite$$HardyZWeinberg$equilibrium$2.-No-gene-flow:--Individuals$cannot$be$added$to$or$subtracted$from$the$popula4on$by$migra4on.$1/11/15$8$Gene-Flow:-movement$of$alleles$from$one$popula4on$to$another$HardyZWeinberg$equilibrium$3.-No-muta*on:--Genes$cannot$change$due$to$muta4on.$Mutation: any heritable change in genetic material. Somatic cells: cells of the body Germ cells: reproductive cells1/11/15$9$Muta*ons-are-spontaneous,-they-occur-by-chance-and-are-random.$Nucleo4de$muta4ons$Chromosomal$muta4ons$Nonrecombinant Nonrecombinant Recombinant Crossing$over$during$meiosis$$!$a$physical$exchange$of$chromosome$parts$Results$in$two$recombinant$&$two$nonrecombinant$chromosomes$function changesadding or losing genetic info1/11/15$10$Muta*on$ No-muta*on$Muta*on$No-muta*on$Genera*on-1$Genera*on-2$Genera*on-3$Genera*on-4$Allele$1$Allele$2$Allele$1$Allele$2$Allele$3$Allele$1$Recombina*on-Allele$4$No-muta*on$Recombination shuffles mutations to produce new sequences. Muta4on$&$Recombina4on$$!$the$two$sources$of$new$gene4c$varia4on$$• A$very$slow$evolu4onary$process$• Random$$Can$be:$• Deleterious$(harmful)$• Advantageous$(beneficial)$$• Neutral$(not$func4onally$important)$Adapta4on$to$the$environment$!$Advantageous$muta4ons$increase$in$frequency$via$posi*ve-selec*on-Deleterious$muta4ons$decrease$in$frequency$via$nega*ve-selec*on-1/11/15$11$An4bio4cs$Z$Resistance$• Evolu4on$via$Muta4on$&$Selec4on$• Asexual$reproduc4on$w/$gene$transfer$(conjuga4on)$HardyZWeinberg$equilibrium$4.-No-gene*c-driM:--Popula4ons$need$to$be$large$enough$to$prevent$allele$frequency$change$due$to$sampling$errors.$CQ-false, c, true, b focuses on large pop1/11/15$12$Popula4on$size$=$4$Popula4on$size$=$40$Popula4on$size$=$400$Frequencies$change$simply$by$chance$Gene*c-driM-acts$more$quickly$to$reduce$gene4c$varia4on$in$small$popula4ons.$Popula*on-BoOlenecks-Founder-effects-something big occurs in that population that greatly affects that population; drastically reduces itfound a new location; not representing original pop1/11/15$13$Popula4on$BoTleneck$–$Northern-Elephant-Seals-• Hunted$in$1890s$to$~20$individuals$• Now$at$~30,000$individuals$$• Greatly$reduced$gene4c$varia4on$HardyZWeinberg$equilibrium$5.-Random-ma*ng:--Individuals$must$not$prefer$some$mates$over$others$(for$that$allele).$$Example:$ $$$Blood$Type$1/11/15$14$Assorta4ve$(nonZrandom)$ma4ng$$$Example:$$Sexual-Selec*on-What-is-a-Species?-####Plural:##Species-$Singular:##Species$(NOT$Specie)$CQ- no;d; b1/11/15$15$Species$Yucca brevifolia Ursus arctos Ulva intestinalis Escherichia coli (15000x) Strongylocentrotus#purpuratus#BIOLOGICAL-SPECIES-CONCEPT--(BSC)-“Species$are$groups$of$actually$or$poten7ally$interbreeding$popula4ons$that$are$reproduc4vely$isolated$from$other$such$groups.” $ $ZErnst$Mayr$$• Must$be$reproduc4vely$compa4ble$$• Must$produce$fer4le$offspring$But…$$BSC$can$be$difficult$to$apply$in$prac4ce$• Asexual$species?$• Ex4nct$organisms?$1/11/15$16$MORPHOSPECEIS-CONCEPT-(Morphologic$Species$Concept)$$Members$of$the$same$species$oden$look$alike.$But$not$always$true…$$$$$Members$of$the$same$species$can$look$very$different.$$sciencemag.org$!$Polymorphic$species$And…$$$$Members$of$different$species$can$look$very$similar.$Chromosome$differences$Cryp4c$Species$compliments