Life Sciences Glossary: Human Chromosomes, Eugenics and Euthenics

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Human Chromosomes

  • Human chromosome preparations were first made by flaming in 1882. First determination of the chromosome number was made by Winiwarter in 1912. He reported 2n = 48. Human Y-chromosome was discovered by Painter in 1923. The correct human chromosome number 2n = 46 was discovered by Trio and Levin in 1956.
  • There are two types of chromosomes, autosomes and sex chromosomes. An autosome is a chromosome other than sex chromosomes. The term ‘autosome’ was introduced by Montgomery in 1904. Sex chromosomes are also called as ‘heteroses’ . The term ‘sex chromosome’ was introduced by Wilson in 1906. The total number of chromosomes in human beings is 46.
  • There are 22 pairs of autosomes and one pair of sex chromosomes. The sex chromosomes constitution of male is XY and of female is XX. Karyotype is the chromosomal complement of an organism. It is made by the arrangement of metaphase chromosome pairs in a standard sequence. In man, there are three classes of chromosomes according to position of centromere. They are metacentric, submetacentric and acrocentric. Telocentric chromosome with terminal centromere is absent in human karyotype. According to size, human chromosomes can be classified into four types, large, medium, small and smallest, the short arm of a chromosome is called as ‘p’ arm and the longer arm as ‘q’ arm. The two sex chromosome of females are identical called XX chromosomes. X- Chromosomes is sub metacentric, corresponds to group ‘C’ of autosomes. The male has one X- chromosomes and a small acrocentric Y-chromosome. Y-chromosomes corresponds to group ‘G’ of autosome. Trisomy is a condition in which the chromosome number is 2n + 1.

Eugenics

The term eugenics was coined by an English scientist Sir Francis Galton in 1883. Galton is called ‘The Father of Eugenics’ as this branch has been started by him. Eugenics is the branch of science which deals with improvement of human race genetically.

Eugenics can be divided into two types:

  • negative eugenics and
  • positive eugenics.

Under negative eugenics, people with inferior and undesirable (dysgenic) traits are prevented from reproducing. Sterilization of men is done by vasectomy involving an operation in which vas deferens or sperm duct is blocked. Sterilization of women is done by tubectomy. This involves an operation in which fallopian tube is blocked. Under positive eugenics, people with better and desirable traits are encouraged.

Euthenics

  • Improvement of the human race by improving the environmental conditions, i.e.. , by subjecting them to better nutrition, better unpolluted ecological conditions, better education and sufficient amount of medical facilities is known as euthenics.
  • Eugenics is the science of being well- born and euthenics is the science of learning to live well.

Euthenics

The symptomatic treatment of genetic disease of man is called euthenics. Euthenics deals with the control of several inherited human diseases, especially errors of metabolism. Branch dealing with genetic engineering is euthenics.

Dysgenics

Dysgenics is the study of undesirable traits of human race and the genes that causes them.

Genetic Engineering

  • Genetic engineering is the latest branch in applied genetics dealing the laboratory alteration of genes. It is also known as bio- technology, recombination DNA technology or gene splicing. Genetic engineering aims at adding, removing or repairing a part of genetic material.
  • Gene splicing is the cutting of DNA molecules at precise points. Plasmids are rings of DNA occurring in bacteria additional to main genome. Plasmids are without vital genes but carry genes for sexuality, antibiotic resistance, etc. Bacteria can survive without plasmids. Now day՚s plasmids are used in genetic engineering. Episode is a plasmid which exists in two states within the bacterial cell, either independently in the cytoplasm or following insertion, as an integral part of the host՚s chromosome. Two enzymes used in genetic engineering are restriction endonuclease and ligases. Restriction endonuclease is used to cut the plasmid as well as the foreign DNA molecules at specific points. Ligase, another enzyme is used to seal gaps or to join bits of DNA.
  • Transfer of live genetic material is involved in transduction and seduction. Transduction is the transfer of bacterial genetic material from one bacterium to another using a phase as the vector. Seduction is the process in which a fragment of genetic material from one bacterium is carried with the sex- factor F to a second bacterium. Genetic engineering helps in the rectification of genetic errors. Microbes can act as biological factories for genetic engineering. Genetic engineering also opens up the possibility of transfer of nitrogen- fixing genes from bacteria or blue green algae to food crops. Genetic engineering permits cloning.

Cloning

Clone is a population of cells or individuals which are genetically identical. There are two types of cloning, ghee cloning at molecular level and cloning of organisms. Cloning is meant for preservation of the genotype of the organism. With the death of an organism, a particular genotype is lost. Free-living organisms in the environment that have had a foreign gene inserted into them are called transgenic organisms. Simian cloning (cloning of Dolly monkeys) was carried out by Don Wolf (USA) in 1996 from an eight – cell embryo. Land Wilmot of Roslyn Institute, Edinburgh, U. K. has produced a clone of adult lamb named “Dolly” (Feb. 1997) . The scientists extracted genetic material from the udder cells of one sheep and implanted it into another sheep՚s egg after removing its genetic material The fused cell developed into an embryo which was planted into another sheep՚s egg after removing its genetic material. The fused cell developed into an embryo which was planted into the uterus of another sheep which acted as surrogate mother. The Scottish scientists who cloned Dolly have now (July 1997) produced Molly and Polly, two lambs cloned with a human gene for blood clotting Factor IX. The milk of ‘Molly’ and ‘Polly’ contains Factor IX that can be extracted for use in treating human haemophilia. Steven Slice and James Roble (USA) have developed a technique for genetically customized calves that will be able to produce medicines for humans in their milk. The first cloned calves George and Charlie were born in January 1998.

DNA Finger Printing

Using DNA fragment lengths, resulting from restriction enzyme cleavage to identify particular individuals.

DNA Prove

A known sequence of DNA that is used to find complementary DNA strands.

Gene Therapy

  • The use of bio- engineered cells or other bio- technology techniques to treat human genetic disorders.
  • Clones of plants are easy to get by vegetative propagation or tissue culture.
  • In India, Her Govind Khorana, who was a Nobel Prize winner is associated with genetic engineering. He synthesized ‘gene’ artificially in a test tube (1969) .
  • First protoplast fusion was done by Harris and Watkins of Oxford using somatic cells of mouse and man.
  • Recent genetic analysis of Dolly՚s DNA has shown that she is a ‘chimers’ , not a perfect clone. Dolly has two genetic mothers as confirmed by the analysis of her mitochondria by Erie Shon and lran Wilmot in 1999. Dolly has nuclear genes from the ewe who supplied the udder cell and mitochondrial genes from the egg cytoplasm of the second ewe.

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