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 phase generate the twin spot of cells homozygous for y and sn y sn m y sn p y sn y sn y sny sn m m mistake p p y sn y sny sn y snGrowth p p m y y yellow y sn y sn patch clone of sn sn singed y sny sn m patch clone of ADULT EXTERIOR m m m m p p site of mitotic recombination a a b b a b c d e f a b c d e f c c Will we see a true twin spot phenotype in this case d d e e daughter cells f Twin spot f a b c d e f a b c d e f What if we had induced a NEW recessive MUTATION on a mutagenized y sn chromosome in the father s sperm that affected cell growth parameters appearance of an ABNORMAL homozygous yellow patch next to homozygous singed patch would SIGNAL that the female carried a new mutant allele y m sn y m sn y m sn y m sn m y m sny m sn p m m mistake p p y m sn m m y m sn m m y m sn p y m sn p p zygote F1 female m mm m odd patch of y y yellow patch of sn sn singed y m sn y m sn m y m sny m sn m p p The inferred abnormal growth behavior of cells in the homozygous yellow patch located next to normal homozygous singed patch would SIGNAL that fact that MOST OF THE CELLS OF THAT F1 FEMALE including her germ cells were heterozygous for a new mutant allele affecting cell growth and such a female would be fully viable even if the 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 odd patch of y y yellow m mm m patch of sn sn singed ADULT EXTERIOR including germ cells hence avoids complications of pleiotropy lethal either because of a defect in the same function affecting adult cuticle or because of a defect in some other process 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 controlled Solution induce using site specific yeast recombination system FLP recombinase protein that catalyzes recombination at FRTs FRT DNA target 34 bp site for recombinase FRT site y sn y sn m p source of FLPase but only induced when where FLPase induced y sn y sn y sny sn m m p p targeted mistake yellow twin spot e g eye precursor cells singed y sn y sny sn y sn m m m m p p y sn y sn m y sny sn m p p lats lats clone in eye l 3 93B l 3 93B clone in eye of lats adult of l 3 93B adult large tumor suppressor Xu et al Develop 121 1053 1995 3rd instar larvae left wildtype right lats lats doomed homozygous lats clone on thorax of lats adult fly Xu et al Develop 121 1053 1995 Genetic mosaics have zillions of uses besides just facilitating mutant isolation and geneticists have ways of controlling exactly when and where FLPase is generated and hence exactly when and where mitotic recombination is induced Sex education from a genetical perspective Forces in evolution and evolution is what genetics and life is really all about 1 Natural selection reproduction of the fittest 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 2 Sexual selection reproduction of the sexiest this term is NOT in your glossary runaway sexual selection generally leads to maladaptive sexually selected traits human brain peacock tail but a tail with the capacity to change the way life evolves Sex Sexual reproduction vs Asexual reproduction Coming together of genetic material from two individuals to form progeny that combine genes from all both parents symmetrical sex us asymmetrical sex bacteria equal genetic contribution from each partner qualitative exceptions mitochondria Y chromosome unequal genetic contribution from each partner Can there be sex without gender males females Recall Sex Sexual reproduction vs Asexual reproduction Coming together of genetic material from two individuals to form progeny that combine genes from all both parents GAMETES sex cells Isogamous sex systems gametes from each parent are of equal size Anisogamous sex systems gametes from each parent are of different sizes Males sperm pollen smaller Females eggs ovules larger parents have to be separate to qualify Sex is ancient and ubiquitous Nevertheless bdelloid rotifers no sex for millions of years Evidence no meiosis genes are missing unusual distribution of DNA variation suggests no gene mixing for ages
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