Office hours Monday 5 6pm door closes 5 15p Friday 4 5 pm 11 Koshland Hall What does a geneticist mean by gene revealed by how a geneticist tests for allelism Alleles DIFFERENT alternative forms of the same gene Given mutant a lozenge shaped eyes vs wildtype mutant b lozenge shaped eyes vs wildtype Are mutant A and mutant B alleles YES A B are alternative forms of the same gene lozengea and lozengeb NO A B are alternative forms of different genes lozengea and lozengelikeb Given mutant a vs wildtype mutant b vs wildtype Before we ask Are mutant a and mutant b alleles First must ask 1 are each of these mutant phenotypes likely to be caused by single gene differences from the wildtype 2 do the mutants map to the same general region of the genome sequencing mutant A and mutant B genomes would not necessarily answer either question Given mutant a vs wildtype mutant b vs wildtype 1 are each of these mutant phenotypes likely to be caused by a single gene differences from the wildtype 2 do the mutants map to the same general region of the genome low resolution segregation tests 1 a a X a a a a only 2 m1 m2 a X m1 m2 alz trihybrid least frequent gamete classes m1 m2 alz m1 m2 a 3 factor cross rule least frequent class two outside parental inside nonparental hence order m1 a m2 Are mutant a and mutant b alleles i e genetic alternatives Do we go with Mendel or high resolution segregation test for recombination complementation test for function phenotype of hybrids breeding behavior of hybrids mutant a mutant b a b OR a b Lewis Benzer mutant a mutant b a a OR b b Are a b alternative units of segregation during meiosis Are a b alternative cis acting units of function during development i e are they segregational alleles i e are they functional alleles Are mutant a and mutant b alleles i e genetic alternatives high resolution segregation test for recombination complementation test for function phenotype of hybrids breeding behavior of hybrids mutant a mutant b a a OR b b must first establish that a b are recessive mutant a wildtype w t phene gametes a b w t not alleles a b ab a ONLY b alleles mutant b wildtype w t phene mutant a mutant b a b OR a b mutant wildtype Phenotype Phenotype complement don t complement not alleles hence one functional copy sufficient alleles Are mutant a and mutant b alleles i e genetic alternatives What about the cis trans test Where is the cis control mutant a mutant b mutant a wildtype w t phene mutant b wildtype w t phene a b in cis complementation test for function phenotype of hybrids a b in trans a b mutant a mutant b OR a b mutant wildtype phenotype phenotype complement don t complement not alleles alleles Are mutant a and mutant b alleles i e genetic alternatives are we being misled by the apparent failure of these recessive mutants to complement in trans When do we need the cis control mutant a mutant b complementation test for function phenotype of hybrids mutant a mutant b could mutants be recessive individually a a OR and in different cis acting b b units of genetic function mutant wildtype i e not be functional alleles phenotype phenotype but interact in combination to complement don t complement appear dominant together not alleles alleles If so the cis control will also be mutant Are mutant a and mutant b alleles i e genetic alternatives CIS control mutant a mutant b we can believe it mutant a mutant b don t appear to complement but can we believe it TRANS phenotype hence functional alleles BUT if mutant phenotype we ve been misled CIS phenotype TRANS mutant phenotype wildtype phenotype CIS phenotype complementation test for function phenotype of hybrids cis vs trans matters cis vs trans doesn t matter TRANS phenotype hence NOT functional alleles Are mutant a and mutant b alleles i e genetic alternatives same recessive mutants in CIS mutant a mutant b wildtype Phenotype we can trust the trans result recessive mutants in TRANS mutant a mutant b CIS TRANS test complementation test for function phenotype of hybrids mutant phenotype don t appear to complement But nobody bothers with the cis control for recessive mutants when doing complementation tests despite what all the textbooks say not even Benzer did it as we will see It is too hard in most cases and in most cases unnecessary then why am I wasting your time with this Are mutant a and mutant b alleles i e genetic alternatives CIS TRANS mutant a mutant b mutant a mutant b CIS TRANS test for functional allelism The true cis trans test will allow us to determine allelism even if one or both of the mutants are not recessive CIS phenotype TRANS phenotype hence functional alleles CIS phenotype TRANS phenotype hence NOT functional alleles and all that matters is whether the cis vs trans phenotypes are the same or different not whether either one is wildtype Remember the complementation test per se is limited to recessive mutants Most mutants are recessive but some of the most useful interesting are not Are mutant a and mutant b alleles i e genetic alternatives complementation test for function alleles as alternative cis acting units of function high resolution segregation test for recombination alleles as alternative units of segregation recombination results may mutant a mutant a conflict mutant b mutant b yet NOT allelic a b may appear to be allelic by the functional test by the functional test failure to complement nonparental alleles recovered by meiotic recombination Mendel said that genes are the units of segregation which led to the beads on a string model of genes chromosomes genetic map linear like chromosome Are mutant a and mutant b alleles i e genetic alternatives complementation test for function alleles as alternative cis acting units of function Conflict favored Intuitively a better operational definition of alternative forms of genes high resolution segregation test for recombination alleles as alternative units of segregation recombination The basis for making genetic maps genetic map linear like chromosome Raises questions If one can get recombination between functional alleles alternative forms of a gene then how do the genetic maps one can therefore construct within single genes compare to the genetic maps that can be had been constructed between genes WHAT IS THE NATURE OF GENETIC FINE STRUCTURE and what is the basic minimal unit of recombination i e what are true segregational alleles American Naturalist v56 p32 1922 bacteriophage Fig 7 20 p228 Phage kill bacteria for a living and
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