On the Function of Flowers 3. The genetics of outcrossing Maintaining heterostyly Self-incompatibility 4. Selfing as a way of life

Darwin’s pollination experiment with the primrose:

Heterostyly is controlled by a gene S with simple inheritance: Ss yields a short-styled flower. ss yields a long-styled flower. Ss  ss -> Ss and ss in a 1:1 ratio S s s Ss ss ss s Ss

Illegitimate pollinations provide a test of the proposed genetic system… Ss (short-styled) flower ss (long-styled) flower. 1:1short:long Ss (short-styled) flower Ss (short-styled) flower. 3:1 short:long ss (long-styled) flower ss (long-styled) flower. all are long s s S s S s s ss ss s Ss ss S SS Ss ss ss ss s ss s Ss s Ss

Pollen and Stigma papilla size go with style length: short-style long-style Pollen and Stigma papilla size go with style length: pollen papillae http://www.biologie.uni-hamburg.de/b-online/e10/19.htm

Pollen and Stigma papilla size go with style length: short-style long-style Pollen and Stigma papilla size go with style length: pollen legitimate unions in red papillae pollen on stigma, legitimate unions http://www.biologie.uni-hamburg.de/b-online/e10/19.htm

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 stigma inhibition is through preventing hydration of pollen on stigma

The Primula supergene: five genes linked together that structurally improve chances of legitimate pollination and inhibit illegitimate pollen G - style length Sp - stigma papilla length I - self incompatibility (sporophytic) P - pollen grain size A - anther height

On the Function of Flowers 3. The genetics of outcrossing Maintaining heterostyly Self-incompatibility 4. Selfing as a way of life

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.

On the Function of Flowers 3. The genetics of outcrossing Maintaining heterostyly Self-incompatibility 4. Selfing as a way of life

aob.oupjournals.org/cgi/reprint/78/6/759.pdf

The control of pollen growth by stigma and style Maintaining heterostyly Self-incompatibility-Campbell p. 788 matching 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)