review session: th apr 5, 7-9 pm (location to be determined) (midterm: m apr 9)
DESCRIPTION
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) - PowerPoint PPT PresentationTRANSCRIPT
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: