What is human genetics?
• The first study in human genetics was carried out by British doctor Sir Archibald Garrod, who in 1909 was able to link the black urine disease, alkaptonuria, to a recessive gene that is inherited like a mendelian factor. Therefore, Garrod is also called father of biochemical genetics and father of human genetics.
• Soon a large number of hereditary traits were studied, e.g., eye colour, skin colour, hair colour, nature of hair, albinism, height, colour blindness, haemophilia, mental ability to taste phenylthiocarbamide (PTC), rolling of tongue, etc.
• The important technique used to study human genetics are. For More Biology Doubts check out Physics Wallah Biology Doubts sections.
1. Pedigree Analysis
It is analysis of diagrammatic record of inheritance of a particular trait or traits over two or more generations in a family tree. The analysis helps in knowing the possibility of presence of a trait in homozygous or heterozygous state in a particular offspring.
2. Population Genetics
The study of distribution of traits and frequency of gene distribution in the entire population is called population genetics. It uses various principles of probability and statistical tools. For autosomal dominant-recessive relationship Hardy-Weinberg equation, principle or law is applied directly.
Gene A = p
Gene a = q
p + q = 1 or A + a = 1
(p + q)2 = p2 + 2pq + q2 = 1
(A + a)2 = A2 + 2Aa + a2 = 1
The normal frequency of dominant trait is 2/3 (p2 + 2pq) while that of recessive trait is 1/3(q2).
Hardy-Weinberg equation is suitably enlarged to include codominants and polygenes.
3. Study of Twins
There are two types of twins, identical or monozygotic and fraternal (non-identical) or dizygotic. Fraternal twins have on the average 50% of their genes in common. The identical twins possess 100% of the genes in common except for an occasional mutation. They provide an excellent opportunity to distinguish effect of environment and heredity on the expression of trait.
With the help of specific stains and other karyotype studies, the effect of chromosomal aberrations has been recorded in case of human beings.
5. Cell culture
This is useful for maintaining living cells. The latter are employed for studying biochemical basis of human genetics, genetic engineering, karyotyping, etc. Karyotyping is done by arresting division at metaphase with the help of colchicines, fixing, squashing and staining. All the chromosomes become clear.