The fact that all living organisms, from the amoeba to the human species, have a cellular structure is well known. However, not everyone thinks about how new creatures appear, according to what laws of nature certain signs are inherited. So, maybe it's time to brush up on the basics of genetics, which are the most important for the evolution of science, forgotten from the school biology course?
Meaning of genes
A living cell is based on genetic material - nucleic acids, consisting of repeating nucleotides, which, in turn, are represented by the sum of a nitrogenous base, a phosphate group and a five-carbon sugar, ribose or deoxyribose. Such sequences are unique, therefore there are no two completely identical living beings in the world. However, the set of genes is far from random, and it comes from the mother cell (in organisms with an asexual type of reproduction) or both parental cells (with a sexual type). In the case of humans and many animals, the final grouping of genetic material occurs at the time of zygote formation due to the fusion of female and male germ cells. In the future, this setprograms the development of all tissues, organs, external features and partially even the level of future he alth.
Basic terms
Perhaps the most important concepts of genetics as a science are heredity and variability. Thanks to the first phenomenon, all living organisms continue their species and maintain world populations, and the second helps to evolve by adding new features and replacing those that have lost their significance. Gregor Mendel, an Austrian botanist and biologist who lived and worked for the benefit of science in the second half of the 19th century, discovered all this and laid the foundations of genetics. He discovered the laws of his theory of heredity through qualitative analysis and experiments on plants. In particular, he used peas most often, since it was easy to isolate the allele in it. This concept means an alternative feature, that is, a unique nucleotide sequence that gives one of two options for the manifestation of a feature. For example, red or white flowers, long or short tail, and so on. However, among them it is worth distinguishing other important terms.
Mendel's first law
Dominant (dominant, predominant) and recessive allele (suppressed, weak) are two signs that influence each other and manifest themselves according to certain rules, or rather, according to Mendel's laws. So, the first of them states that all hybrids obtained in the first generation will carry only one trait obtained from parent organisms and prevailing among them. For example, if the dominant allele is the red color of flowers, and the recessive allele is white, then when two plants are crossed withwith these traits we get hybrids with only red flowers.
This law is true if the parent plants are pure lines, that is, homozygous. However, it is worth pointing out that there is a small amendment in the first law - codominance of features, or incomplete dominance. This rule says that not all signs have a strictly predominant influence on others, but can appear simultaneously. For example, parents with red and white flowers have a generation with pink petals. This is because although the dominant allele is red, it does not have full influence on the recessive, white. And therefore, a third type of color appears due to the mixing of signs.
Mendel's Second Law
The fact is that each gene is denoted by two identical letters of the Latin alphabet, for example "Aa". In this case, the capital sign means a dominant trait, and the small one means recessive. Thus, homozygous alleles are designated "aa" or "AA", since they carry the same trait, and heterozygous alleles - "Aa", that is, they carry the rudiments of both parental traits.
Actually, the next Mendel's law was built on this - about the splitting of features. For this experiment, he crossed two plants with heterozygous alleles obtained in the first generation of the first experiment. Thus, he received the manifestation of both signs. For example, the dominant allele is purple flowers, and the recessive allele is white, their genotypes are "AA" and"aa". When crossing them in the first experiment, he received plants with the genotypes "Aa" and "Aa", that is, heterozygous. And upon receipt of the second generation, that is, "Aa" + "Aa", we get "AA", "Aa", "Aa" and "aa". That is, both purple and white flowers appear, moreover, in a ratio of 3: 1.
Third Law
And the last law of Mendel - about the independent inheritance of two dominant traits. It is easiest to consider it by the example of crossing different varieties of peas with each other - with smooth yellow and wrinkled green seeds, where the dominant allele is smoothness and yellow color.
As a result, we will get different combinations of these traits, that is, similar to the parent ones, and in addition to them - yellow wrinkled and green smooth seeds. In this case, the texture of the peas will not depend on their color. Thus, these two traits will be inherited without affecting each other.
