Human Genetics Summary

• The branch of genetics concerned with the study of inheritance of human traits is called human genetics.

• An extension of knowledge of genetics applied to improve quality of human race is called eugenics.

• Sir Archibald Garrod is commonly described as Father of human genetics for pointing out that the inborn errors of metabolism are controlled by genes and inherited in a Mendelian pattern.

• About 200 traits are known to be genetically transmitted in human beings, some through typical Mendelian pattern and some in accordance with non- Mendelian principles.

• There are five basic approaches that are followed for studying human inheritance: they are, pedigree analysis, population genetics, cell culture, human cytology and study of twins.

• Pedigree analysis helps in tracing the transmission particular traits through generation.

• Population genetics involves the study of distribution traits in a given basis of inheritance.

• Culturing of human cells invitro, help in understanding the biochemical basis of inheritance.

• Human cytology and karyotyping helps in ascertaining the number, shape size and structural features of chromosomes.

• Study of monogygotic twins helps in distinguishing between hereditary and environmental factors.

• Human genetics has progressed so much that tailoring of phenotypes and human cloning seem to be a possibility in the near future.

• Diseases that are known to be inherited from the parent to the offspring are known as genetic diseases.

• Genetic diseases are caused due to the expression of recessive genes.

• Genetic disorders are of two basic types autosomal and allosomal.

• Autosomal disorders are metabolic disorders caused by the expression of defective, recessive genes present on the somatic chromosomes. Hence, they express equally in both the sexes.

• Albinism is a common autosomal disorder. It is characterised by the total absence of melanin in the skin, caused by the expression a homozygous recessive gene.

• Phenyl Ketonuria (PKU) is a metabolic disorder seen in growing children. In this condition an enzyme phenyl pyruvic hydroxylase necessary for amino acid metabolism, is not produced. It is also due to the expression of an autosomal recessive gene.

• Sickle cell anaemia is a condition where defective haemoglobin is produced and the RBC become crescent shaped, affecting the supply of oxygen to the tissue cells. It occurs due to a mutated gene.

• Allosomal disorders are caused by genes present on the sex chromosomes. Such disorders express more commonly in males than in females. Colour blindness and haemophilia are common examples.

Certain genetic disorders are caused due to a condition called aneuploidy which involves a change in the chromosome number.

• Aneuploidy most often occurs due to non-disjunction: a failure of separation of homologous chromosomes during prophaseI of meiosis.

• Nondisjunction results in the formation of trisomy (2n+1) or monosomy (2n-1).

• Non-disjunction in sex chromosomes results in the formation of defective individuals with Klinefelters syndrome (44 A + XXY) or Turners syndrome (44A + XO).