Genes

There are several commonly observed human traits. Chromosomes are composed of DNA tightly packed and coiled around blocks of protein known as histones. Humans have a total of 46 chromosomes made up of 1 pair of sex chromosomes and 22 pairs of autosomes. There are several minimally invasive procedures for detecting birth defects in humans during early pregnancy (prenatal diagnosis). Gene linkage occurs when genes that are close together are inherited as a set in autosomes or sex chromosomes. The interrelationships of parents and their children across many generations is called a family tree or pedigree and can be derived by tracing traits across several generations. Sex-linked disorders are genetic defects carried by the X chromosome. Autosomal disorders can be recessive or dominant. Disorders can result from the alterations in chromosome number in autosomes or sex chromosomes. When the integrity of chromosomes is affected, other disorders occur. This chapter explores this aspect of genes.