ABSTRACT
This chapter outlines the basic elements of genetics. It describes the types of genetic tests now available to help in neonatal diagnosis. The chapter provides an approach to the diagnosis of congenital abnormalities. The basic unit of inheritance for any species is the gene. A gene can also be considered in another way as a specific length of deoxyribonucleic acid (DNA), which encodes a particular function, in most cases the synthesis of a protein. The genetic code in DNA is transcribed into a molecule called messenger RNA (mRNA). Chromosome abnormalities can broadly be classified into abnormalities of chromosome number or a rearrangement of a normal number of chromosomes. Robertsonian translocation is a particular type of translocation involving chromosomes that bear very short p arms with little genetic information, termed acrocentric chromosomes. Single-gene disorders have one of three principal modes of inheritance: autosomal dominant, autosomal recessive, and X-linked recessive.
