Genetics. To most people, genetics are mysterious particles involved in the transmission of traits
from generation to generation. To geneticists, genetics is little more than a branch of molecular
biology that deals with the adventures of DNA within the cell and the effects that are observed in
that cell, and the organism this cell may be a part of.
Many of us have been taught the classical Mendelian transmission of traits in high school science.
But as one dwelves deeper, this black and white model becomes shades of grey... and colors, too!
Without going into the science behind this, there are several other phenomena that can change the
Mendelian model. Keep those in mind while you hybridize your daylilies!
- Some traits travel together - Suppose that the gene for the yellow
color and the gene for carved flowers are on the same chromosome, and worse still, next to each other
on that chromosome. When pollen and ovules are produced, their maternal and paternal genes are shuffled,
or more accurately, recombined, before giving rise to a haploid gamete (an ovule or pollen grain containing only
half the number of chromosomes rather than a pair of each). The closer two genes are on a single chromosome,
the smaller the likelihood of a recombination fork occuring between them. If that was the case for the gene for
yellow color and the gene for carved flowers, it would be very rare to cross a white (if white was a mutant
version of the yellow gene and thus also closed to the 'carved' gene) and find within the progeny a flower
that is both white and carved. I fact, depending on how close the genes are, it might take thousands of
progeny before finally seeing a white carved flower. Furthermore, neighboring genes often belong to the
same biochemical pathway. For instance, you could have all the genes for color production in the same general
area of single chromosome. I don't know this for a fact for daylilies or any other flowers, but beware that
some pesky genes can be nearly inseparable friends.
- Maternal inheritance - Two organelles found in the cell (and outside
the nucleus) contain their own DNA. These are mitochondria and plastids (aka chloroplasts, the photosynthetic organelle of plants). The pollen
grains need to travel light and don't pack mitochondria and plastids in their tiny little luggage. Thus every
mitochondria and plastid within a plant comes from the pod (female) parent. What processes does the plastid genome
contain, and what effect do these genes have on the plant? There are only 2-300 genes in the plastid, mostly
important for photosynthesis and photorespiration. What are the practical implications? If you want to
transmit vegetative characteristics such as plant vigor and speed of growth, try to use the more
vigorous plant as the pod plant. The pod plant is more likely to transmit vegetative characteristics to its
offspring than the pollen plant, providing the genes responsible for the vigor are found in the plastids. We don't
know for sure what makes any given plant more vigorous than another are on the plastid, but it's a good idea to
edge one's bets.
- Dominant vs. recessive - No, it's not that simple. In fact, it's
been said that Mendel was very lucky in his choice of the pea plant for his studies, because as it turned out,
the genetics were very simple. Had he picked another plant, he might not have made the discoveries he became
famous for long after his death. We too sometimes have to knock on wood, and cross our fingers.