MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

BIOLOGY

CHAPTER 1. BIOLOGICAL FOUNDATIONS OF HUMAN VITAL ACTIVITY

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.2. Basics of human genetics

Organismal level of trait inheritance

Inheritance is The process of transmitting Genetic information across generations. The term "trait inheritance" is used conventionally. It is not traits themselves that are inherited, but genes carrying information about all the traits and Properties of the Organism. The Selection/27.html">Realization of Genetic information occurs during reproduction and individual development under specific environmental conditions.

The regularities of trait inheritance at the organismal level were first established in 1865 by G. Mendel through Hybridization experiments using various varieties of garden pea. These regularities are now known as Mendel's three laws and the law of segregation of Gametes. These constitute the fundamental laws of genetics. Mendel's success was ensured by his wise choice of the research object and the application of the hybridological method he developed himself. The garden pea (Pisum sativum) is a self-pollinating plant, which makes it possible to keep the studied traits pure. The scientist carefully planned his experiments, maintained precise quantitative records, and subjected his findings to mathematical analysis. The experimental design formed the foundation of the hybridological method, which became the primary method of both classical and modern genetics.

The hybridological method involves analyzing trait inheritance through hybridization (crossing). The heterozygous organism produced in this process is called a hybrid, and its offspring are referred to as hybrid progeny. The Main principles of the hybridological method are: 1) using parental organisms that have shown no trait variation in prior trials (homozygous); 2) crossing organisms that differ distinctly not in their entire complex of traits, but in only one or a few pairs of alternative traits; 3) precise quantitative accounting of the expression of each individual pair of alternative traits across generations; analysis covers not only the first generation derived from the cross, but also the progeny of each individual hybrid. Prior to G. Mendel, scientists studied the inheritance of numerous traits simultaneously and failed to achieve the expected results.

A cross in which the parental organisms differ in a single pair of alternative traits is called monohybrid, in two pairs—dihybrid, and in three or more pairs—polyhybrid.

Another major contribution of G. Mendel was his Introduction of algebraic symbols for designating genetic cross diagrams, which, with minor additions, are still used in modern genetics. In these diagrams, parents are conventionally denoted by the letter P (from Lat. parentes — parents), a cross by the multiplication sign ×, the female sex by the symbol ♀ (Venus's mirror), the male sex by ♂ (Mars's shield and spear), a dominant allele by an uppercase Latin letter, a recessive allele of the same Gene by the corresponding lowercase letter, and the hybrid generation by F (from Lat. filii — children) with a numerical index indicating the sequence number: F₁ — the first generation, F₂ — the second, and so on. The first line of the diagram shows the genotypes of the parents (traditionally placing the female organism first and the male second), the second line shows the types of gametes they produce, and the third line displays all possible genotypes of the offspring.