1. Review session: Th Apr 5, 7-9 pm (location to be determined)
(midterm: M Apr 9)

2. Reading on sex:
pp85-88 (In many species…)
pp review (Analysis of rare mistakes…)
pp (Changes in chrom. # --to--Some euploid…)
Table 14.2 (p526)
pp (RNA splicing helps regulate gene expression)
pp except (Sex determination in Drosophila…)

3. 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

4. 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?

5. 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+

6. ..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

7. 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

8. 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

9. (“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: )

10. homozygous lats clone on thorax of lats/+ adult fly
(Xu et al, Develop.121: )

11. 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

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

13. (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

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

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

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

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

18. 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

19. 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)

20. 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