The largest database of twins
What are the twins hidingOleg Lischuk, MedNovosti
The researchers plan to contact half a million pairs of twins, about 300 thousand of which they expect to include in the database being created. This is an order of magnitude greater than the volume of existing banks of similar data.
If the twins agree to the researchers' access to the information, their DNA samples and medical information provided by the UK National Health Service will be included in the database. This service will also participate in the financing of the project, the estimated cost of which, depending on the total amount of data, ranges from 6 to 20 million pounds.
The database is designed to provide material for scientific research in the field of inheritance of various human qualities. Most of these studies are conducted using information about twins.
The fact is that gemini is a unique material for studying the role of the environment and genetic factors in the formation of various individual characteristics of a person – from behavior and character to predisposition to serious diseases.
If statistical observations show that children from the same family have more similarities than from different families, it is impossible to find out what exactly caused these similarities. The role can be played by both inheritance of genes from the same parents, and the influence of the same environmental factors – housing and material conditions, nutrition, cultural environment, upbringing, education, etc.
Studies of twins make it possible to separate the influence of genetics from the influence of the environment. To do this, scientists compare the commonality of a trait in monozygotic and dizygotic twins.
Monozygotic (identical) twins appear when the embryo, which appeared as a result of fertilization of one egg, is divided into two parts at the early stages of development, each of which develops into an independent organism. Such twins have the same set of genes and are copies of each other (with age, due to the influence of environmental factors, minor differences may appear between them).
For the appearance of dizygotic (fraternal) twins, it is necessary that their mother, for some reason, ripen two eggs in one menstrual cycle. As a result of their fertilization by different spermatozoa, twins appear, who are essentially ordinary brothers or sisters. Like any siblings, dizygotic twins have about half of the same genes. Their value for researchers lies in the fact that they are born on the same day and grow up in identical conditions.
The simplest method of research using twins is based on the fact that the environmental conditions of both mono- and dizygotic twins growing up in the same family are equally similar. The fundamental difference between them lies only in the degree of coincidence of genes: 100 percent – in identical and about 50 percent – in fraternal.
Therefore, the differences between monozygotic twins growing in a similar environment will be due only to random factors. The differences between dizygotic twins from the same family depend, in addition to random factors, on the mismatch of some genes. If we observe the frequency of occurrence of the studied trait in large groups of identical and fraternal twins and compare them, we can conclude about the role of genes and the environment in the development of this trait.
More complex modifications of this assessment method have also been developed, using more complex statistical models of the occurrence of signs and covering twins who developed under different environmental conditions.
With the help of gemini research methods, it is possible to determine the role of genetics in the appearance of a variety of signs quite accurately – from eye color and intelligence level to individual character traits and predisposition to specific diseases.
For example, with the help of twins, it was possible to establish that heredity affects the development of almost any trait to one degree or another. Moreover, the effect on some signs (for example, height) can be very strong, on some (for example, the level of intelligence) – moderate, and it can be more complex when different genes affect different elements of the trait (for example, autism or diabetes). One of the curious results of twin studies was the fact that the psychological characteristics of identical twins, whom their parents considered to be fraternal, and identical twins, whose parents were not mistaken in their identity, coincide equally.
It should be noted that a number of experts in statistical genetics, theory of statistics and psychology have sharply criticized the research of twins. The most common statements are that assessments of the heritability of a trait are based on unreasonable assumptions, that the similarity of environmental factors is controversial, that the data obtained on twins are not applicable to all people, that studies of twins can only be of the nature of observation, not exposure, and others. The design of most modern research deprives most of these statements of validity.
Despite the criticism, the number of studies conducted worldwide with the help of twins is constantly growing. Thanks to them, valuable data has already been obtained on the role of heredity in the development of diseases, the formation of psychological and behavioral characteristics of a person and other areas. So, the twins helped scientists identify genetic factors for the development of serious diseases such as asthma, diabetes, multiple sclerosis and many others. And recently, with their help, American scientists have found out that the age of the onset of sexual activity also depends on genes.
Portal "Eternal youth" www.vechnayamolodost.ru06.04.2009