Monohybrid crossbreeding is a crossbreeding characterized by the difference in parental forms from each other in the presence of one pair of alternative, contrasting characters. A sign is called any feature of the organism, any its property or quality, by which it is possible to distinguish individuals. In plants, such a property is, for example, the shape of the corolla (asymmetric or symmetrical), its color (white or purple), etc. Maturation speed (late ripening or early maturity), as well as resistance or susceptibility to certain diseases, are also signs. .
All properties in the aggregate, starting with external and ending with certain features in the functioning or structure of cells, organs, tissues, are called a phenotype. This concept can be used in relation to one of the available alternative features.
The manifestation of properties and traits is carried out under the control of existing hereditary factors - in other words, genes. Together, genes form a genotype.
Mendel hybrid crossbreeding is represented by pea crossbreeding. At the same time, there are such quite clearly visible alternative properties as white and purple flowers, green and yellow color of unripe beans, wrinkled and smooth surface of seeds and others.
Carrying out monogybrid crossbreeding, G. Mendel, an Austrian botanist of the 11th century, found that in the first generation (F1), all hybrid plants had purple flowers, while white color did not appear. Thus, the first Mendel law on the uniformity of first-generation samples was introduced. In addition, the scientist found that in the first generation, all samples were homogeneous and for all seven of the traits he studied.
Thus, monohybrid crossbreeding suggests for individuals of the first generation the presence of alternative traits of only one parent, while the properties of the other parent seem to disappear. The predominance of properties G. Mendel called dominance, and the signs themselves - dominant. The scientist called the non-manifesting qualities recessive.
Carrying out monohybrid crossbreeding, G. Mendel self-pollinated first-generation hybrids grown. The scientist sowed the seeds formed in them again. As a result, he received the next, second generation (F2) hybrids. In the obtained samples, splitting according to alternative characteristics in an approximate ratio of 3: 1 was noted. In other words, three quarters of individuals of the second generation had dominant properties, and one quarter had recessive properties. As a result of these experiments, G. Mendel concluded that the recessive trait in the samples was suppressed, but did not disappear, appearing in the second generation. This generalization is called the "Law of Splitting" (the second law of Mendel).
The scientist carried out further mono-hybrid hybridization in order to identify how inheritance will occur in the third, fourth and next generations. He grew samples using self-pollination. As a result of the experiments, it was revealed that plants whose signs are recessive (white flowers, for example), in subsequent generations reproduce offspring only with these (recessive) properties.
Plants of the second generation behaved somewhat differently, whose properties were called dominant by G. Mendel (owners, for example, of purple flowers). Among these samples, the scientist, analyzing the offspring, identified two groups that have absolute external differences for each specific attribute.
For individuals that differ in two ways, dihybrid crosses are used. The tasks of determining genotypes and phenotypes are relatively simple; Mendel’s laws are applied to solve them.