Mendel's laws. Fundamentals of Genetics
Gregor Mendel is an Austrian botanist who studied anddescribed the pattern of inheritance of characters. Mendel's laws are the basis of genetics, which to this day play an important role in studying the influence of heredity and the transmission of hereditary traits.
In his experiments, the scientist crossed variousTypes of peas that differ in terms of one alternative: a shade of flowers, smooth-wrinkled peas, the height of the stem. In addition, the distinctive feature of Mendel's experiments was the use of so-called "clean lines", i.e. offspring resulting from self-pollination of the parent plant. Mendel's laws, formulation and brief description will be discussed below.
For many years studying and scrupulously preparingexperiment with peas: special bags protecting flowers from external pollination, the Austrian scientist achieved incredible at that time results. A careful and lengthy analysis of the data obtained allowed the researcher to deduce the laws of heredity, which later became known as "Mendel's Laws."
Before proceeding to describe the laws, several concepts need to be introduced to understand this text:
Dominant gene - gene, the sign of which is manifested in the body. It is indicated by the capital letter: A, B. When crossed, such a sign is considered conditionally stronger, i.e. it will always manifest itself in the event that the second parent plant has conditionally less weak signs. Which proves Mendel's laws.
Recessive gene - the gene in the phenotype is not manifested, although it is present in the genotype. Denoted by a capital letter a, b.
Heterozygous - a hybrid in whose genotype (a set of genes) there is both a dominant and a recessive gene of some trait. (Aa or Bb)
Homozygous - hybrid, He possesses exclusively dominant or only recessive genes, responsible for a certain attribute. (AA or bb)
Below we will consider Mendel's laws, briefly formulated.
The first law of Mendel, also known as the law of uniformityhybrids, can be formulated as follows: the first generation of hybrids obtained from the crossing of pure lines of paternal and maternal plants does not have phenotypic (ie, external) differences in the trait under study. In other words, all daughter plants have the same shade of flowers, the height of the stem, the smoothness or roughness of the peas. Moreover, the manifested sign phenotypically exactly corresponds to the initial sign of one of the parents.
Mendel's second law or the splitting law states: offspring from heterozygous first-generation hybrids in self-pollinating or related crossover has both recessive and dominant traits. Moreover, splitting occurs according to the following principle: 75% - plants with a dominant trait, the remaining 25% - with recessive. Simply put, if the parent plants had red flowers (a dominant trait) and yellow flowers (a recessive sign), then the daughter plants for 3/4 will have red flowers, and the rest will be yellow.
The third And last Mendel's law, which is also called the law of independentinheritance characteristics, in general terms means the following: when crossing homozygous plants that have 2 or more different characteristics (that is, for example, a tall plant with red flowers (AABB) and a low plant with yellow flowers (aabb), the studied signs (stalk height and color shade) are inherited independently, in other words, high plants with yellow flowers (Aabb) or low with red (aaBb) can result in crossing.
The laws of Mendel, discovered in the middle of the 19th century,much later received recognition. On their basis, all modern genetics was built, followed by selection. In addition, the laws of Mendel are evidence of the great diversity of the now existing species.