The Twin Method

The twin method of research is used whenrevealing the conditionality of the characters of a hereditary nature. This method demonstrates the relationship between the genotype and the environment. The twin method of genetics made it possible to evaluate the importance of genetic predisposition to many pathologies, expressiveness, penetrance, and the conditions for the appearance of certain types of diseases. The research data are very useful in the quantitative assessment of hereditary determinacy (determinateness) of certain characteristics. In this regard, the twin method is considered one of the most important research methods in quantitative heredity.

Twins can be the same-sided. They are formed in the early stages of the division of the zygote, in which organisms (full-fledged) develop from two (less often more) blastomeres. Identical twins have a genetic identity.

The authorship of this research method is attributed to F. Galton.

Despite the opportunities that possessestwin method, today it does not have a wide practical application, as before. This is due to the discovery of more accurate modern research techniques that make it possible to uniquely identify a hereditary predisposition to a specific pathology.

The twin method involves the comparison of dizygotic and monozygotic twins (offspring, which consists of single-bodied single-born mammals).

Monozygotic offspring develops in onethe fertilized egg. These twins have 100% of the total genes. Thus, the differences revealed between them, with the hereditary factor are not related. Development of dizygotic twins occurs in different ovules, which are fertilized by different spermatozoa. This offspring possesses 50% of the general genes, as in ordinary siblings (descendants of one pair of parents - brothers, sisters). However, their simultaneous birth, joint education forms factors of the general environment. Thus, the degree of difference in the desiotic progeny is determined by the degree of difference in genotypes.

As a result of comparing the data of the two groupstwins are calculated indicators of discrepancy (discordance) and compliance (concordance). In addition, a calculation is made of the frequency at which a symptom or disease develops in each of the above-mentioned hereditary group.

The twin method is divided into several stages:

1. The stage of sampling.
2. The stage of determining the type of zygote.
3. The stage of evaluating the results when comparing pairs.

The above-described research method was of great importance in the study of heredity in behavior, many infectious and "multifactorial" (caused by several reasons) pathologies.

In human genetics not onlyclassical, but also a modified method of twin study. So, to study the possibilities to improve some of the intellectual characteristics using psychological training, the method of control by the partner is used, and in the study of diabetes, the technique of twin families.

Heredity of psychological featuresintellect and personality is convenient to observe in descendants separated in the early or infancy, brought up separately and not under the influence of the general environment and special interaction with each other.

However, reliable data can not be obtained fromalways. This is due to the systematic differences between non-twins and twins for certain characteristics, as well as social and psychological characteristics in the development process in the postnatal period. These factors limit the scope of the method described above.