1. From hermaphrodites to males and females

2. The degree of outcrossing ranges from…
perfect
imperfect
hermaphrodites
monoecy
dioecy 0%
100%

3. Perfect flowers: 90% of angiosperms are hermaphrodites
The ancestral and basal condition is hermaphroditic

4. The benefits of outcrossing often outweigh the drawbacks
Avoids inbreeding depression
Promotes heterozygosity
Promotes genetic variability
Drawbacks
Environmental conditions may limit pollen flow
"Cost" of having two parents, only one of which bears seed
Unwanted gene flow

5. Even with perfect flowers, there are ways of encouraging, or even requiring, outcrossing
Structural differences
Heterostyly
Pin-eyed primrose
Thrum-eyed primrose

6. Even with perfect flowers, there are ways of encouraging, or even requiring, outcrossing

7. Even with perfect flowers, there are ways of encouraging, or even requiring, outcrossing
Male sterility

8. Male sterility for hybrid rice production – using CRISPR-Cas9

9. Imperfect flowers – encouraging and/or obliging outcrossing
The basis of sex determination is selective abortion of flower organs: The "basal condition" is hermaphroditic; different species differentiate at different times

10. Monoecy 
Zea mays 
Plant achieves a vegetative to reproductive transition 
Selective elimination of pistils in tassel florets and stamens in ear florets 
Mutants cause variation in these patterns – can get pistils in tassels and stamens in ears 
Source: passel.unl.edu

11. Monoecy 

12. Monoecy plus self-incompatibility
Covering the bases in hazelnut. (Corylus spp.)
Self incompatibility can reinforce separation of sexes on the
same plant.  

13. Monoecy + SI Incompatibility in Hazelnut One S-locus, 30 alleles
Co-dominance in Stigmas
Dominance or Co-dominance in Pollen
Fluorescence Microscopy
If the same allele is expressed by the stigma
and the pollen, the cross is incompatible
Source: S. Mehlenbacher, OSU

14. Incompatibility testing using fluorescence microscopy in hazelnut
Compatible
Excellent germination
Long parallel tubes
Incompatible
Poor germination
Short tubes, bulbs
Source: S. Mehlenbacher, OSU

15. Monoecy + male sterility (MS) Covering the bases in maize
MS: Nuclear or cytoplasmic (CMS)
Example of CMS - Zea mays “T” cytoplasm
Mitochondrial / nuclear gene interaction
Pleiotropic effects: sterility and disease susceptibility
More on male sterility and hybrid rice

16. Dioecy
Distinguishing feature: sex chromosomes. Parallels to XY (mammals) and X:A ratio (Drosophila)
Humulus lupulus
Plant achieves a vegetative to reproductive transition 
Selective elimination of organs in staminate and pistillate flowers
Sex-determining genes concentrated on X and Y chromosomes
XX = female; XY = male

17. Dioecy Evolution of sex chromosomes from autosomes
Accumulation of sex-determining genes on a single chromosome with no homolog prevent recombination between sex-determining genes
Create ~ equal numbers of male and female offspring theoretically leads to degeneracy of Y – except for “maleness” genes. But the Y chromosome is not inert
Y chromosomes are in a permanent haploid state

18. Dioecy

19. Dioecy
Example: Asparagus officinalis: Using doubled haploids to produce YY “super males” Males are XY or YY
Males have increased vigor and therefore optimum for production
XX x YY = all male (XY)