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)