Every summer resident or gardener knows what heterosis is. Another thing is that often we simply do not correlate this biological concept and the effect it causes with this complex word. And although in the fundamental scientific environment to this day there are disputes about the mechanisms and the effect exerted by heterosis, the layman has long been using it in everyday life. In the article, we will try to clearly and clearly explain what heterosis is, what effect it causes and how it is used in human economic activity.
Academic knowledge
Heterosis is in biology a phenomenon of the “strength of hybrids”, namely an increase in vitality, rapid growth and larger sizes of hybrids in the first generation in comparison with parent organisms. Filial 1 or F1, as the descendants of the first generation are designated, if the parents were not of the same species, may have the effect of heterosis, or it may be that it will not be. In subsequent generations, changes do not occur. The effect of heterosis is not always beneficial for a particular organism. As you know, hybrids are often low fertility (the ability to reproduce prolific offspring) up to infertility.
Discovery story
What is heterosis, namely the strengthening of hybrids, was known even before Mendel’s inheritance laws. The term was introduced in 1914 by the American biologist W. Shell. But back in 1765, the Russian naturalist and biologist I. Kelreiter was the first to describe the hybrid power of the descendants of shag and panicle tobacco, obtained by him during artificial cross-pollination of plants. And C. Darwin even wrote a separate work on the power of hybrid forms - “The effect of cross-pollination and self-pollination in the plant world” (1876). Hybrid seeds of corn in bulk were obtained by D. Bill at the Michigan Agricultural College in 1878.
Mechanism: complementation or overdomination
What is heterosis from the point of view of its mechanisms is the question today. There are two theories among competent scientists about the mechanism of this phenomenon:
- The theory of complementarity explains the phenomenon of amplification of hybrids by the "inclusion" of genes, which were in the parental forms in the homozygous (aa or AA) state. In the first generation of hybrids, the heterozygous gene allele (Aa) causes heterosis.
- Theory of overdomination. According to this version, heterosis is due to the increased dominance of dominant alleles in hybrids and the disconnection of gene repressors (inhibitors). The key role is played by the theory of gene hierarchy, according to which there are key regulators in the genome - genes that play an important role in the inclusion of certain genes.
Recent studies of molecular biology, however, prove the presence of mechanisms of complementation and overdomination in heterotic hybrids, and the presence of key “switches” of genes that order music in the genome realization orchestra.
Types of heterosis
The following types of this phenomenon are distinguished:
- The reproductive form in which there is an increase in fertility and better development of the reproductive organs, seeds or fruits.
- Somatic heterosis is due to the coincidence of alleles and the great development of autonomic and somatic organs.
- The adaptive form enhances the viability and stability of hybrid organisms.
Heterosis in nature and human activities
In nature, interspecific closely related interbreeding arose along with sexual reproduction. And in evolutionary teaching there is even one of the ways of speciation - hybridization. Man has been using the effect of heterosis since time immemorial. For example, horse and donkey (or one-humped camel) hybrids are known for their strength and increased stamina. The hybrid “bister” form obtained from the crossing of beluga and sterlet is actively used in fish farming, as it grows faster than the parent forms. In crop production, we have long switched to hybrid crop production. The performance of hybrids of corn, onions, tomatoes, cucumbers and bell peppers is 25% higher than the clean lines (indicated by “F1” on the seeds).
Heterosis in humans: jerry and mong
The effect of heterosis manifests itself in interracial marriage. This topic is quite sensitive, especially in the context of pseudoscientific speculation on the degeneration of the nation and other populist statements. But genetics and molecular biologists unequivocally declare - heterosis is caused by the same mechanisms during interethnic marriages, and the general biological parameters of the offspring can be higher than the parent ones. When the effect of heterosis manifests itself (which is more likely with the purity of national characteristics in parents), people are called the word "jer" from GeteRozis, GR. If the effect of heterosis does not occur, the general parameters of the children will be worse than the parent ones. Such people are called “Mong” by MONGrel.
And finally
For mankind, the last 100-150 years have become years of development of transport communications and population migration, the destruction of class, religious and ethnic obstacles. This led to the mixing of nations and nationalities, interracial and interethnic marriages. And maybe the effect of heterosis in biology is the increase in population growth in most countries by 5-15 cm and the onset of puberty by 13-14 years, instead of 16-18 only 100 years ago?