Plant Breeding & Genetics
February 29, 2016
This article was originally published in 2013 and appeared in Garden Culture Magazine UK, Issue 2, under the title, “Genetics and Breeding”.
That offspring resemble each other is a fact that has been well known for ages. In the past, differences were attributed to superstition and supernatural powers. But scientist Gregor Mendel discovered in the 19th century that these differences can be explained, and can even be mathematically predicted. Genetics has always been the key point in plant breeding, but now breeders apply more scientific and calculating methods than ever before.
WHAT ARE GENES?
Genes are a blueprint, a kind of manual statement of what should happen in a given situation. They are made up of code, what we call the DNA code. DNA is comprised of a double helix, which means that two long strands of code are twisted around each other.
A gene never stands alone. In the same strand, one can find dozens, hundreds, or even thousands of genes. These strands are often quite long and are called chromosomes. It is these chromosomes that make us who we are, physically speaking. Normally, an organism has a fixed number of chromosomes, though how many depends on the species. Chromosomes normally appear – with exceptions – in pairs, with one derived from the ‘father’, and one from the ‘mother’.
HOW DOES BREEDING WORK?
Breeders play a game of chance. They combine two organisms and hope that this will create a more useful combination. But they also leverage the laws of genetics, which allow for the increase in certainty that specific properties can be passed down to the offspring.
In practice, genes can occur in various forms. Each different form of a gene is called an “allele.” Not all alleles are the same. There are dominant and recessive alleles (i.e. submissive). In the event that an organism contains both a dominant and recessive gene, only the code of the dominant gene will be expressed. Hence, an organism must inherit both a recessive gene from the father and the mother for the recessive gene to be dominant and have an impact on the organism.
The offspring can be influenced by preventing a particular trait in a population. It is possible to calculate how certain alleles, and thus individual organisms or “phenotypes” can be realized by intentionally cross-breeding with the appropriate parent. Even with the right knowledge, this remains a game of chance and becomes considerably more complicated if more trait properties are taken into account. The number of individuals that is necessary in order to obtain the desired hybrids will, therefore, increase as attention is paid to more and more specific aspects.
WHAT IS F1?
In the breeding of plants, one often encounters the term ‘F1’. This refers to the first generation. In many cases, crossing two very different subspecies within a plant species, the properties of the parents can surface more in the “child” than in the parental line itself. This advantage will again be reduced within the next generation, which is commercially interesting because offspring of F1 plants are less potent, making it necessary to obtain seeds again.
(Editor’s Note: So, you see, those F1 hybrids in seed catalogues are far removed from GMOs. While you cannot grow the same plant again from saved seed, they produce perfectly safe to eat harvests, though the gardener may want to use only organic F1 seed.)
Using modern techniques, DNA can be analyzed, and the information gained put to good use. Analyzing DNA is widely done, and it is very important to find out which property is associated with which piece of code. Unfortunately, this is not always clearly indicated by the DNA and is often guesswork.
However, as soon as it is known which piece of code relates to a particular gene, it is possible to test individuals for the presence of this gene. In this way, suitable plants can be selected for further breeding with higher speed and accuracy.
Genetic modification also makes use of these DNA techniques but takes it one step further by copying genes from one organism to another. With this technique, it is also possible to utilize genes from completely different organisms. After all, DNA is a universal code.
WANT TO LEARN MORE?
Since the discovery of genetics, breeding has been elevated from an art to a science. Genetics is a very broad topic which is not easily understood by the layman. Years of study are required to learn all the details. This article only covers the tip of the iceberg. The rest of that iceberg contains a lot of math, logic, and more complicated terms that would require significant study to understand. Genetics is the source of life, and is therefore very important for everyone, whether one is aware of it, or not.