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3. The genetics of outcrossingMaintaining heterostyly
Self-incompatibility 4. Selfing as a way of life
On the Function of Flowers
Darwin’s pollination experimentwith the primrose:
Ss ss -> Ss and ss in a 1:1 ratio
S s
s
s
Ss
Ss
ss
ss
Ss yields a short-styled flower.
Heterostyly is controlled by a gene S with simple inheritance:
ss yields a long-styled flower.
Illegitimate pollinations provide a test of the proposed genetic system…
S s
s
s
Ss
Ss
ss
ss
Ss (short-styled) flower ss (long-styled) flower.1:1short:long
S s
S
s
SS
Ss
Ss
ss
s s
s
s
ss
ss
ss
ss
Ss (short-styled) flower Ss (short-styled) flower.3:1 short:long
ss (long-styled) flower ss (long-styled) flower.all are long
http://www.biologie.uni-hamburg.de/b-online/e10/19.htm
Pollen and Stigma papilla size go with style length:
papillae
pollen
short-style long-style
http://www.biologie.uni-hamburg.de/b-online/e10/19.htm
Pollen and Stigma papilla size go with style length:
papillae
pollen
short-style long-style
pollen on stigma,legitimate unions
legitimate unionsin red
Two kinds of self-incompatibility:Gametophytic:
S1S2 female S1S3 male yields inhibition of S1 pollen, not of S3 pollen
--- happens in the style
Gametophytic self-incompatibility continued:
Inhibition is through enzymes moving into pollen tube from style.
Evidence lies in a protein found in styles of petunias with incompatible pollen tubes, not with compatible tubes -
Multiple alleles are found in species to allow a diverse definition of self---at least 75 in whiter clover and 150 in red clover.
Two kinds of self-incompatibility:
Sporophytic:
S1S2 S1S3 does not yield inhibition of pollen Only the same two alleles yield inhibition
--- happens on the stigmainhibition is through preventing hydration of pollen on stigma
G - style length
Sp - stigma papilla length
I - self incompatibility(sporophytic)
P - pollen grain size
A - anther height
The Primula supergene:five genes linked together
that1. structurally improve
chances of legitimate pollination and
2. inhibit illegitimate pollen
3. The genetics of outcrossingMaintaining heterostyly
Self-incompatibility 4. Selfing as a way of life
On the Function of Flowers
Selfing plants have little flowers, often without petals, and grow in disturbed terrain
chickweed
Violets have two kinds of flowers, one for outcrossing, one for selfing.
3. The genetics of outcrossingMaintaining heterostyly
Self-incompatibility 4. Selfing as a way of life
On the Function of Flowers
aob.oupjournals.org/cgi/reprint/78/6/759.pdf
The control of pollen growth by stigma and style
1. Maintaining heterostyly2. Self-incompatibility-Campbell p. 788matching alleles at the s locus prevent pollen success
(the haploid allele matches either of the diploid style alleles)
--gametophytic (RNAses from style invade pollen tube and shut it down - Ros, Leg, Sol)
--sporophytic (signal transduction prevents germination of pollen on stigma, perhaps by preventing hydration - Bra)