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 m p y- sn+ y+ sn- m p m p y+ y- sn+ sn- mistake Growth y- sn+ m patch (clone) of y/y (yellow) sn/sn (singed) y- sn+ p y+ sn- ADULT EXTERIOR m y+ sn- p

a b c d+ e+ f+ daughter cells a+ b+ c+ d e f a b c d+ e+ f+ c+ d e f site of mitotic recombination a b c d+ e+ f+ daughter cells a+ b+ c+ d e f a b c d+ e+ f+ c+ d e f a+ b+ Twin-spot Will we see a true twin-spot phenotype in this case?

y+ y- sn+ sn- m- m+ y- sn+ sn- y+ yellow singed odd patch of y/y 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? m- m+ ..appearance of an ABNORMAL homozygous yellow patch next to homozygous singed patch would SIGNAL that the female carried a new mutant allele m p y- sn+ sn- y+ mistake yellow singed odd patch of y/y patch of sn/sn m- m+ zygote (F1 female) m-/m- m-/m+

..and such a female would be fully viable even if 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 were heterozygous for a new mutant allele affecting cell growth including germ cells (including her germ cells) ..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 hence avoids complications of pleiotropy yellow patch of sn/sn singed …lethal either because of a defect in the same function affecting adult cuticle, or because of a defect in some other process m-/m- m-/m+ ADULT EXTERIOR

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- y- sn+ sn+ y- sn+ sn- y+ y+ sn- sn- y+ source of FLPase y- m p y+ y- sn+ sn- source of FLPase FRT site y- sn+ y+ sn- m p m p y- sn+ sn- y+ targeted “mistake” p m y- sn+ y+ sn- yellow singed twin-spot …but only induced when & where FLPase induced e.g. eye precursor cells

(“large tumor suppressor”) lats/lats clone in eye of lats/+ adult (“large tumor suppressor”) l(3)93B/l(3)93B clone in eye of l(3)93B/+ adult 3rd instar larvae left: wildtype right: 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 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

.. .from a genetical perspective Sex education .. .from a genetical perspective

(and evolution is what genetics -- and life -- is really all about): 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) maladaptive sexually selected traits runaway sexual selection generally leads to

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

equal genetic contribution from each partner symmetrical sex: us qualitative exceptions: mitochondria & Y chromosome unequal genetic contribution from each partner asymmetrical sex: bacteria

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 bdelloid rotifers: no sex for millions of years Nevertheless: Evidence: no meiosis (genes are missing) unusual distribution of DNA variation suggests no gene mixing for ages