1. Hybridological analysis

The set of investigation methods for hereditary characteristics of an organism (its genotype) is the genetic analysis.

Depending on the purpose and features of the object being studied genetic analysis is performed on a population, organismal, cellular and molecular levels.

The basis of genetic analysis is hybridological analysis - analysis of the nature of signs inheritance with the help of crosses. HA lies in hybrids production and their further comparative analysis in a number of generations (the analysis of splitting).

Hybridological analysis principles:

1. Usage as original individuals (parents) forms which do not give splitting during crossing, i.e. constant form – pure breeding lines.

2. Individual pairs of alternative signs inheritance analysis, that is, signs that appear only in two mutually eliminating variants.

3. Quantitative account of the forms that appear in the course of successive crossings and mathematical methods usage in processing the results.

4. Individual analysis of the progeny of each parent individual.

5. Based on crosses results mating diagram is compiled and analyzed.

Hybridological analysis is usually preceded by the breeding method. With its usage the selection or creation of original material for further researches is carried out. Gregor Mendel, the founder of hybridological analysis, starts with getting constant homozygous forms of garden pea (true breading lines) by self-pollination. He decided to find out the rules of pea individual traits inheritance and for 8 years studied over 10 000 plants of 22 true breading lines.

In some cases, it’s difficult to apply the method of direct hybridological analysis. For example, in studying the inheritance of traits in humans, crosses cannot be planning; the number of children is a few, puberty lasts for a long time. So besides hybridological analysis in genetics, in particular, in anthropogenetics used many other methods.

2. Genealogical method

Genealogical method (pedigree) allows us to trace the inheritance of traits in families. It is used for determination of the hereditary or non-hereditary trait nature, for study of the regularities of hereditary traits transmission in successive generations in the greatest possible number relatives, for study of sex-linked inheritance or inheritance coupled with other characteristics, for study of mutation process, especially in cases where it is necessary to distinguish the newly emerged mutations from those that are run in families, that is, having in previous generations.

Conclusions of medical genetic consultation are based on genealogical method used not only for diagnosis but also for prognosis.

Genealogical method involves drawing up pedigree with highlighted the members of the family who have studied sign. A person, whose pedigree is analyzed, is called proband or propozyt. Proband’s brothers and sisters are called sibs (siblings). When compiling genealogies symbols proposed in 1931 by G. Yust are used.

Pedigree analysis

A pedigree is a systematic listing (either as words or as symbols) of the ancestors of a given individual, or it may be the "family tree" for a large number of individuals. It is customary to represent females as circles and males as squares. Matings are shown as horizontal lines between two individuals. The offspring of a mating are connected by a vertical line to the mating line. Different shades or colors added to the symbols can represent various phenotypes. Each generation is listed on a separate row labeled with Roman numerals. Individuals within a generation receive Arabic numerals. Let solid symbols represent black guinea pigs and open symbols represent white guinea pigs.

Figure. Pedigree of guinea pigs