Genetic mosaics have zillions of uses besides just facilitating mutant isolation

1. 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

2. Sex education .. .from a genetical and evolutionary (= genetical) perspective

3. Sex: --- understanding its biological significance -- appreciating how genetics was used to understand how it is determined. … according to Jacob Bronowski in “The Ascent of Man” (1973) Mendel himself was inspired by the clear-cut difference between males and females and the 1:1 sex ratio

4. runaway sexual selection generally leads to maladaptive ("unfit") sexually selected traits 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) reproduction of the sexiest (2) Sexual selection: (this term is NOT in your glossary)

5. peacock tail human brain = ? …but a tail with the capacity to change the way life evolves

6. Sex: Sexual reproduction vs. Asexual reproduction Coming together of genetic material from (two) individuals to form progeny that combine genes from all (both) parents

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

8. Can there be sex without gender? (males & females)

9. 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

10. Isogamous sex systems: gametes from each parent are of equal size Anisogamous sex systems: gametes from each parent are of different sizes GAMETES (sex cells) Males: sperm/pollen (smaller) Females: eggs/ovules (larger) (parents have to be separate to qualify) (hate to disappoint those who think male/female labels are politically incorrect)

11. Nevertheless: bdelloid rotifers: no sex for millions of years Sex is ancient and ubiquitous Evidence: no meiosis (genes are missing) unusual distribution of DNA variation suggests no gene mixing for ages

12. (1) Males dilute females’ genetic contribution (the couple is the unit of reproduction) Costs of sex: (2) Seeking a mate and mating takes time and energy -- and is dangerous (3) Sexual conflicts arise (remember the Haig hypothesis for imprinting) (4) Sex and its consequence, recombination, break up winning gene teams

13. (3) Help to keep ahead of parasites (there is no “optimal” genotype in the real world) Benefits of sex: (1) Reduces mutational load (escape “Muller’s ratchet” -- irreversible loss of genes) perhaps males particularly useful (rationale for “maladaptations” from sexual selection) (2) Free good mutations from bad genetic backgrounds

14. “Sex determination genes” determine two qualitatively different things (a distinction not often appreciated, even by those who study the genetic programming of sex): population sex ratio sexual dimorphism (developmental differences including those that determine behavioral differences)

15. An extreme example of sexual dimorphism Bonellia viridis sex is determined by whether: larva lands on rock Female: 100 mm Male: 1 mm larva lands on adult female ESD: environmental sex determination

16. relevant variables for ESD: Host (Bonellia) Temperature (turtles, alligators) Neighbor density (parasitic wasps) “Presence of male” (tropical fish) vs. GSD: genotypic sex determination Segregation of alleles (genes) determines sex best for generating 1:1 sex ratios

17. apparant paradox: Since females are rate-limiting for reproduction, why see 1:1 sex ratio so often? (as usual, Darwin had the answer first) In the aggregate, both sexes contribute equally to the next generation, regardless of population sex ratio (every female needs a male) hence, the minority sex on average will make a disproportionate contribution per individual Natural selection will favor generation of the minority sex. At 1:1, no minority sex!

18. w -/w -(white eyed) Females X Males (red eyed)w+/Y XX w -/w+(red) daughters expected: XY w -/Y (white) sons “exceptions”: XXY white daughers (fertile) X(O) red sons (sterile) xredXY XXY white daughers (fertile) progeny are “secondary” exceptions XY(±Y) red sons (fertile!) 1:1 for fruit flies: XX femalesXY males …but what really determines fly sex? Calvin Bridges (1916): (primary) (xxx & o/Y die)

19. Y chromosome does not detemine sex (but is required for male fertility) Sex-chromosome difference CAUSES X chromosome number determines sex (triggers) different sexual development for fruit flies: normal: XX femalesXY males abnormal: XXY femalesXO males

20. absolute number: 1=male, 2or more = female odd vs. even (paired?) XX X=male? number relative to ploidy (non-sex chromosomes)? X AA male, but X A female? XX femalesXY males What about X-chromosome number matters? …again, genetic exceptions to the rule provide the answer

21. px bw + X Females Males px + sp + bw sp px + & + sp Parental types: XXX AAA Nonparental types: + + & px sp (recombinant) ( 6.5 cM) X px bw sp Male Three, not two, parental types recovered: px bw + + bw sp px + sp highest freq. &= numbers (autosomal genes) expected testcross PROGENY phenotypes: ALSO: one unusually large ++ female (2) many intersexual (sterile) progeny XXY AAA (3) normal and jumbo daughters

22. (dead) female X A X:A=1, (1921 2007, and not what Bridge's thought or what the textbooks say) For fruit flies: X(±Y) AA X:A = 0.5, male XX AA X:A = 1, female XX(±Y) AAA X:A = 0.67, intersex (phenotypic mosaic) XXX AAA X:A= 1, female (jumbo) X:A ratio sex-determination mechanism What is it about ploidy changes that affects the way that X-chromosome dose determines sex?