Y – linked Inheritance

A trait due to a mutant gene carried on the Y-chromosome but with no counterpart on the X – is called a Y – linked or holandric (“wholly male”) trait. It is direct transfer of trait from father to all sons. This trait appear in all males in every generation. (For example, hairy ears, bilateral radio-ulnar synostosis. In this trait the radius and ulna bones of both arms are fused.

III. Study of twins or twinic method is studying the genetic features in twins. Twins was born (occurs, about 1% cases in total amount of births.

Monozygous. The identical twins develop from a single zygote by separation of the two blastomeres after the first cleavage. Therefore, they have similar genetic traits, and same sex except for rare chance mutation.

Dizygous orfraternal twins develop from different zygotes. Therefore, they are no more alike than other children born at different times in the same family. They may have different sex and have about 50% similar genetic traits.

Since the identical turns carry the same genotype, their study helps in distinguishing between hereditary and environmental characters.

The traits that are similar in the identical twins are considered hereditary, and the features in which they differ are regarded environmental.

Twins, which similar by phenotype are called concordant (latin, concord are – be agree) if trait present in both partner.

If twins hare differences in phenotype and trait present only in one of twins, such twins are called discordant. Than more concordant ness than more importance of heredity in development of trait. Blood groups entire determine by genotype. Epilepsy, Diabetes, Shizofreny, hypertonic disease determined by environmental factors.

The studies on identical and fraternal twins help to understand both heredity and variations like the role of the genotype, environmental influence and the probability factor of inheritance of traits in humans.

IV. Population-statistical method or population genetics. It is striding of spreading and distribution of hereditary traits and genes which controlled it in different groups of people on certain areas.

The term population refers to the total number of individuals of a species occupying a particular geographic area at a given time. A species has many populations inhabiting different regions.

All genes separated info categories:

1) having universal spreading, for example gene of infantile Amaurotic Idiocy (Tay-Sach’s Disease) due to an error in fat metabolism, child brain and spinal cord are damaged, this results in mental retardation and paralysis. The child dies in 3 or 4 years. This is caused by recessive gene in homozygous condition 1% people of Europe affect by this gene;

Gene of red-green colour blindness is the inability of certain human beings to distinguish red from green colour. It is a sex-linked trait, and is preducted by a recessive gene, which present in 7% of males and 0,5 % females, but in heterozygous condition this gene present in 13% of females.

2) genes spreading in certain regions, for example sickle anemia is a hereditary disease found widely in tropical Africa and also in American blacks whose ancestors came from that part of Africa. It is characterized by sickle-shaped (crescentic) red blood cells formed under low oxygen conditions. Change in the shape of red blood cells is due to the presence in them of a defective type of hemoglobin called hemoglobin S, gene of inborn dislocation of hip found in North-east of Russia.

Population-statistical method helps to study probability of individual with certain genotype in this population or relative marriages.

It helps to define the frequency of carrier of in recesses gene heterozygous condition.

V. Cytogenetic methods. Term “cytogenesis” was introduced by Sutton in 1903. Cytogenesis is a branch of branch of Biology, is very helpful in the study of human genetics.

It is study of number, structure and functions of chromosomes with help of light microscopy.

The correct number of somatic chromosomes in man was not known 1956. New techniques of staining chromosomes have revealed their correct number and this has greatly helped the study of human genetics.

The techniques of cultivating human cells in specific media and the techniques of somatic cell genetics have enabled geneticists to understand the biochemical basis of the inheritance of many characters.

Culture of cells can be received from piece of skin (fibroblasts), bone marrow, embryonic tissues, chorion, limps nodes, cells of amniotic fluid, lymphocytes of blood (WBC).