MEDICAL BIOLOGY, ANATOMY, HUMAN PHYSIOLOGY AND PATHOLOGY - Y.I. Fedoniuk 2010

BIOLOGY

SECTION 1. BIOLOGICAL FOUNDATIONS OF HUMAN LIFE

1.4. ONTOGENETIC LEVEL OF LIFE ORGANIZATION

1.4.2. Fundamentals of Human Genetics

Marriage Systems and Medico-GENETIC ASPECTS OF the Family

In humans, the allelic composition of offspring genotypes depends on the marriage system. Marriages are classified into non-assortative and assortative, outbreeding, Inbreeding, and incestuous marriages. In non-assortative marriages (panmixia), any individual has an equal probability of marrying any individual of the opposite sex. Assortative marriages are unions between individuals with similar phenotypes. They are subdivided into positive and negative assortative marriages. In the first case, individuals with similar phenotypes marry more frequently, while In the second case, such marriages occur less frequently than expected. For instance, marriages between deaf-mutes, as well as between individuals of similar height or intellectual capacity, are observed more often than would be expected under panmixia. Conversely, red-haired men and women tend to avoid marrying each other. Outbreeding refers to non-consanguineous marriages, whereas inbreeding refers to consanguineous marriages. Incestuous (prohibited) marriages are a form of inbreeding involving first-degree relatives (father-daughter, brother-sister). Historically, this form of inbreeding existed as a system within the Ptolemaic dynasty, which ruled Egypt from 305 to 30 BC. Today, such marriages are prohibited almost everywhere. In many states, marriages between nieces/nephews and uncles/aunts are forbidden. In the United States, more than a third of the states prohibit marriages between first cousins. In high-altitude Swiss villages and Jewish communities in many German cities, the frequency of cousin marriages reaches 6-12%. A high frequency of consanguineous marriages is typical of small human populations isolated by geographical, economic, religious, national, or racial factors.

The Medical and Genetic significance of various marriage systems: 1) inbreeding increases homozygosity, including for pathological genes; close consanguineous marriages lead to increased infant mortality and a higher probability of Hereditary diseases with an Autosomal Recessive Inheritance pattern; 2) outbreeding maintains a high level of heterozygosity, which may result in enhanced viability.