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 sn

m

py+

y- sn+

sn-

mm

pp

y- sn+

sn-

y- sn+

y+

y+ sn-

mistake

y- sn+

y- sn+

y+

y+ sn-

sn-

mm

pp

mm

pp

p

m

pm

y- sn+

y+

y+ sn-

sn-

y- sn+patch (clone) ofy/y (yellow)

patch (clone) ofsn/sn (singed)

ADULTEXTERIOR

Growth

a b c d+ e+ f+

a+ b+ c+ d e f

site of mitotic recombination

daughtercells

a b

a b c d+ e+ f+

c+ d e f

a+ b+ c+ d e f

c d+ e+ f+a+ b+

Twin-spot

Will we see a truetwin-spot phenotypein this case?

m

py+

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+

mm

pp

y- sn+

sn-

y- sn+

y+

y+ sn-

mistake

y- sn+

y- sn+

y+

y+ sn-

sn-

mm

pp

m

m

pp

p

m

pm

y- sn+

y+

y+ sn-

sn-

y- sn+

yellow

singed

odd patch ofy/y

patch ofsn/sn

m-

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 allele

yellowsinged

odd patch ofy/y patch of

sn/sn

The (inferred) abnormal growth behavior of cells in the homozygous yellow patchlocated next to “normal” homozygous singed patch

would 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 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.

m-/m-

m-/m+

ADULTEXTERIOR

…lethaleither because of a defectin the same functionaffecting adult cuticle, or becauseof a defect in some other process

henceavoids complicationsof pleiotropy

includinggerm 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 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

p

m

pm

y- sn+

y+

y+ sn-

sn-

y- sn+yellow

singed

twin-spot

y- sn+

y- sn+

y+

y+ sn-

sn-

mm

pp

m

m

pp

mm

pp

y- sn+

sn-

y- sn+

y+

y+ sn-

targeted “mistake”

m

py+

y- sn+

sn-

sourceof FLPase

FRT site

…but only inducedwhen & whereFLPase induced

e.g. eye precursor cells

lats/lats clone in eyeof lats/+ adult

(“large tumor suppressor”)

l(3)93B/l(3)93B clone in eyeof l(3)93B/+ adult

3rd 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 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

(2) Sexual selection: reproduction of the sexiest

maladaptive sexually selected traits

runaway 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 evolves

human brain = ?

Sex: Sexual reproductionvs. Asexual reproduction

Coming together of genetic material from (two) individuals to form progeny that combine genes from all (both) parents

symmetrical sex:

asymmetrical sex:

equal genetic contributionfrom each partner

unequal genetic contributionfrom each partner

qualitative exceptions:mitochondria & Y chromosome

us

bacteria

Can there be sex without gender?

(males & females)

Sex: Sexual reproductionvs. Asexual reproduction

Coming together of genetic material from (two)

individuals to form progeny that combine genes

from all (both) parents

Recall:

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)

Sex is ancient and ubiquitous

no meiosis (genes are missing)

unusual distribution of DNA variationsuggests no gene mixing for ages

Evidence:

bdelloid rotifers: no sex for millions of years

Nevertheless: