Review session: Th Apr 5, 7-9 pm(location to be determined)(midterm: M Apr 9)Reading on sex:pp85-88 (In many species…)pp109-110 review (Analysis of rare mistakes…)pp516-518 (Changes in chrom. # --to--Some euploid…)Table 14.2 (p526)pp664-665 (RNA splicing helps regulate gene expression)pp669-676 except 670-71 (Sex determination in Drosophila…)DNA breaks and improper repair after S phasegenerate the “twin-spot” of cells homozygous for y and snmpy+y-sn+sn-mmppy-sn+sn-y-sn+y+y+sn-mistakey-sn+y-sn+y+y+sn-sn-mmppmmpppmpmy-sn+y+y+sn-sn-y-sn+patch (clone) ofy/y (yellow)patch (clone) ofsn/sn (singed)ADULTEXTERIORGrowtha bc d+e+f+a+b+c+d e fsite of mitotic recombinationdaughtercellsa ba b c d+e+f+c+d e fa+b+c+d e fc d+e+f+a+b+Twin-spotWill we see a truetwin-spot phenotypein this case?mpy+y-sn+sn-What if we had induced a NEW recessive MUTATION on a mutagenizedy- sn+ chromosome (in the father’s sperm) that affected cell growth parameters?m-m+mmppy-sn+sn-y-sn+y+y+sn-mistakey-sn+y-sn+y+y+sn-sn-mmppmmpppmpmy-sn+y+y+sn-sn-y-sn+yellowsingedodd patch ofy/ypatch ofsn/snm-m-m+m+m-m+m-m+m-m-m+m+m-/m-m-/m+zygote (F1 female)..appearance of an ABNORMAL homozygous yellow patch next to homozygoussinged patch would SIGNAL that the female carried a new mutant alleleyellowsingedodd patch ofy/ypatch ofsn/snThe (inferred) abnormal growth behavior of cells in the homozygous yellow patchlocated next to “normal” homozygous singed patchwould SIGNAL that fact thatMOST OF THE CELLS OF THAT F1 FEMALE were heterozygous for a new mutant allele affecting cell growth..and such a female would be fully viableeven ifthe new recessive mutant allele would have been lethal(perhaps even embryonic lethal -- killing long before adult stage)if a significant fraction of her cells had been homozygous for it. m-/m-m-/m+ADULTEXTERIOR…lethaleither because of a defectin the same functionaffecting adult cuticle, or becauseof a defect in some other processhenceavoids complicationsof pleiotropyincludinggerm cells(including her germ cells)Problems (limit use for genetic screens):-- mitotic recombination infrequent-- position of exchange not controlled-- radiation used to induce is damaging-- tissues in which occurs are not controlledSolution:induce using site-specific yeast recombination systemFLP: recombinase (protein that catalyzes recombination at FRTs)FRT: DNA target (34 bp) site for recombinasepmpmy-sn+y+y+sn-sn-y-sn+yellowsingedtwin-spoty-sn+y-sn+y+y+sn-sn-mmppmmppmmppy-sn+sn-y-sn+y+y+sn-targeted “mistake”mpy+y-sn+sn-sourceof FLPaseFRT site…but only inducedwhen & whereFLPase inducede.g. eye precursor cellslats/lats clone in eyeof lats/+ adult(“large tumor suppressor”)l(3)93B/l(3)93B clone in eyeof l(3)93B/+ adult3rd instar larvaeleft: wildtyperight: lats/lats (doomed)(Xu et al, Develop.121:1053 1995)homozygous lats clone on thorax of lats/+ adult fly(Xu et al, Develop.121:1053 1995)Genetic mosaics have zillions of usesbesides just facilitating mutant isolation…and geneticists have ways of controllingexactly when and where FLPase is generated…and henceexactly when and where mitotic recombination is inducedSex education.. .from a genetical perspectiveForces in evolution (and evolution is what genetics -- and life -- is really all about):(1) Natural selection:reproduction of the fittest(2) Sexual selection:reproduction of the sexiest maladaptive sexually selected traitsrunaway sexual selection generally leads to…remember, responses to changes in biological environment (including parasites)are as important as responses to changes in physical environment.(this term is in your glossary)(this term is NOT in your glossary)peacock tail…but a tail with the capacity to change the way life evolveshuman brain = ?Sex:Sexual reproductionvs. Asexual reproductionComing together of genetic material from (two) individuals to form progeny that combine genes from all (both) parentssymmetrical sex:asymmetrical sex:equal genetic contributionfrom each partnerunequal genetic contributionfrom each partnerqualitative exceptions:mitochondria & Y chromosomeusbacteriaCan there be sex without gender?(males & females)Sex:Sexual reproductionvs. Asexual reproductionComing together of genetic material from (two)individuals to form progeny that combine genesfrom all (both) parentsRecall:Isogamous sex systems:gametes from each parent are of equal sizeAnisogamous sex systems:gametes from each parent are of different sizesGAMETES (sex cells)Males: sperm/pollen (smaller)Females: eggs/ovules (larger)(parents have to be separate to qualify)Sex is ancient and ubiquitousno meiosis (genes are missing)unusual distribution of DNA variationsuggests no gene mixing for agesEvidence:bdelloid rotifers: no sex for millions of
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