i23 – Inheritance of Human Genetics

human genetics, study of the inheritance of characteristics by children from parents. Inheritance in humans does not differ in any fundamental way from that in other organisms. The study of human heredity occupies a central position in genetics. Much of this interest stems from a basic desire to know who humans are and why they are as they are. At a more practical level, an understanding of human heredity is of critical importance in the prediction, diagnosis, and treatment of diseases that have a genetic component. The quest to determine the genetic basis of human health has given rise to the field of medical genetics. In general, medicine has given focus and purpose to human genetics, so the terms medical genetics and human genetics are often considered synonymous. The prevailing concept of heredity in Gregor Mendel’s time was that the traits of the parents become blended in the progeny, as though the hereditary material consisted of fluids that become permanently mixed when combined. However, Mendel’s observation that one of the parental characteristics was absent in F1 generation and reappeared in unchanged form in the F2 generation was inconsistent with the idea of blending. Mendel’s experiments were simple and direct and revealed the most significant principles that determine how characteristics (traits) are passed from parents to offspring. Due to his careful analysis of inheritance of traits in garden peas carried out from 1856 to 1963 and published in 1866, heredity came to be recognized as a biological process separate from development. The Mendelian principles are the basis of ‘transmission genetics’ also referred to as ‘formal genetics’ because the subject can be understood and the rules clearly seen without any reference to the biochemical nature of genes or gene products. Mendel’s story is one of the great legends in the history of  cience.

Although Mendel’s work demonstrated that the units of heredity are stable and particulate but at that time the biological basis of the transmission of genes from parents to offspring was quite mysterious; neither the role of the nucleus in reproduction nor the details of cell division were known. The early geneticists began to wonder about the biochemical nature of the gene and raised questions like what kind of molecule is a gene. How can hereditary information be contained in a molecule? How can this information be transmitted from parents to offspring? In what way is the information different in a mutant? At that time, there as no logical starting point for such an investigation. In 1869, Friedrich Miescher discovered a new type of mild acid, abundant in the nuclei of white blood cells that turned out to be chemical substance of which genes are made and is called deoxyribonucleic acid (DNA). However, the connection between DNA and heredity was not demonstrated.