More advanced cytogenetic techniques to observe chromosomes have been developed
since the mid-1950s, and are now being combined with molecular tools in the field of
plant genomics research.Fluorescencein situhybridization(FISH) is a method that utilizes
small fluorescently labeled DNA fragments to paint different chromosomes (Fig. 2.10).
In this technique, nuclear DNA is fixed to the surface of a slide preparation and the
labeled DNA fragments bind to chromosomes with homologous complementary sequences.
Since the chromosomes are still in the nucleus, it is said to be in situ, or in the original
location.Flow cytometryis a technique to determine the total amount of DNA within a
cell. Although this is not a direct way to visualize chromosomes, it allows researchers to
determine (along with chromosome number) genome size, that is, how much genetic
material is present in a cell, which has implications during hybridization between species.
2.4 Plant Reproductive Biology
2.4.1 History of Research
When it comes to sex, angiosperms have evolved many ways of doing it and indeed of
doing without it. Sexuality in plants (reviewed in Stuessy 1989) was first demonstrated
experimentally over 300 years ago by a German botanist and physician, Rudolph Jakob
Camerarius. In his 1694 bookEpistolae de Sexu Plantarum(Letter on the Sexuality of
Plants), he identified the stamen and pistil as the male and female organs, and the pollen
as the fertilizing agent (Camerarius 1694). By the mid-1700s the role of insects in pollina-
tion was well accepted, and in 1793 another German, Sprengel, provided elaborate details
on the floral adaptations of 500 or more species to insect pollinators (Sprengel 1793).
Charles Darwin was also interested in pollination and plant mating systems from an evol-
utionary perspective, and one of his books outlining The Effects of Cross and Self
Fertilisation in the Vegetable Kingdomin 1876, introduced the idea of self-incompatibility
Figure 2.10.Fluorescent in situ hybridization (FISH) shows the physical location of a specific trans-
gene or DNA. The inset (bottom left; courtesy of Chris Pires) showsBrassica napusmitotic metaphase
chromosomes stained blue with two different centromere probes (red and green). See color insert.
34 MENDELIAN GENETICS AND PLANT REPRODUCTION