The fact that human genetics can answer questions related to diseases in human beings, their treatment, genetic disorders and more importantly, human nature, makes this field interesting. It includes different fields such as classical and clinical genetics and genomics.
Human genetics deals with the study of inheritance patterns in human beings. The potential uses of human genetics in the study of human nature and its prospective applications in medicine have made it a subject of interest for one and all.
Gregor Mendel studied the inheritance of traits in living beings. He concluded that inheritance depends upon discrete units known as genes and he came up with a model of inheritance. He deduced that the inheritance of traits follows certain laws. For his significant work in the field, Mendel is known as the father of genetics.
Inheritance traits in human beings are either autosomal or X or Y linked. Autosomes are the non-sex chromosomes whereas the X-linked and the Y-linked genes are found on the sex chromosomes.
In case of autosomal recessive inheritance, a trait or disorder is passed on in families. For a recessive trait to show in humans, two copies of the gene responsible for that trait are required.
Since two copies are needed, the trait or disorder can remain hidden for generations together in case only one copy is present. Many may even be unaware of the fact that they are acting as carriers of the trait or disorder.
Autosomal dominant inheritance is a pattern wherein a single copy of the gene of a trait is sufficient for it to appear. If one of the parents has this trait, it can be displayed in their children.
Traits inherited from the sex chromosomes include X-linked and Y-linked inheritance. X-linked genes can be autosomal or recessive. Recessive X-linked disorders are common among males. As a father passes his Y chromosome to his son, X-linked traits or disorders are inherited from the maternal side.
The expression of X-linked traits in females depends on their zygosity for the trait. When a female is homozygous for a particular trait or disorder, it means that she carries two identical copies of the gene affecting that trait. In case she is heterozygous for a particular disorder, it means that she has two different alleles for that disorder.
Homozygous females display X-linked disorders while heterozygous females become carriers for the disorder. Y-linked disorders are carried on the Y chromosome. As it is present only in males, a Y-linked trait is transferred from a father to his son.
Apart from the nuclear DNA, human beings possess mitochondrial DNA. It is believed that the mitochondria are descended from a proteobacterium, which merged with eukaryotic cells, around two billion years ago. Mitochondrial DNA is about 16 KB long.
A human being inherits mitochondria from his/her mother. This makes it evident that DNA can be used to track a person's maternal lines. In some species like mussels or in insects like honeybees, paternally inherited mitochondria are observed. A single case of paternal inheritance of mitochondria was reported in humans. It was associated with infertility.
Genes play a vital role in personality characteristics and human behavior. Facial features are linked to the genetic constitution of an individual.
A human being inherits characteristics like facial dimples, color of the iris, the structure of the earlobe and other such traits through genes. Attributes such as the overall stature and susceptibility to certain diseases are also inherited genetically.
Human genetics has evolved to a level where we have been able to manipulate the genetic constitution of an embryo to a certain extent through genetic engineering. The knowledge of human genetics has led us to be able to enhance the positive traits in humans and reduce or remove the negative ones.
The various interesting aspects of human genetics have unfolded mysteries of the physical and psychological characteristics of human beings and opened doors to the betterment of human life.