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COURSE Principles of inheritance and variations Lesson 3 Important terms used in genetics -1 Dr. Praveen Kumar Agrawal M.Sc., Ph.D., CSIR NET (JRF). SRF, GATE 21 Years of Pre-medical teaching experience
GENETICAL TERMS AND SYMBOLS While studying Genetics we come across certain technical terms. Students should be familiar with these terms for understanding the basic concepts of genetics. These terms are as follows. 1. Character or Trait .Characters are the visible feature of the organism and can be experienced physically. For example-height of the plant, colour of the flower, shape of the seed, colour of the eyes etc. Each character may have two or more alternative forms. .These alternative forms of a character are called allelomorphic characters. For example The height of the plant may have long and dwarf alternatives .In this case height of the plant is the character (trait) but its length and dwarfness are the allele-morphic character. .When a character has only two sharp alternatives than such alternatives are called contrasting characters
2. Gene or Factor Gene is a unit portion of DNA, which carries the information for the formation of a character. Since DNA is located in chromosomes, genes are also present in chromosomes .When chromosomes are passed on to the next generation, the genes associated with these chromosomes are also passed on to the next generation, carrying the message for the formation of characters . The message for the formation of characters in a gene (DNA) is written in genetic code language (refer next chapters). The message is decoded to form some specific proteins. These proteins in turn govern the formation (expression) of the characters. Mendel was not aware of the genes and their protein forming nature. He used the term 'factor for the unit of character transmission. 3. Homologous Chromosomes In a diploid cell, all chromosomes are present in the form of pairs. Each pair has two morphologically similar kinds of chromosomes. These two chromosomes of a pair are called homologous chromosomes. .Genes, which are present on one chromosome (of a homologous pair), have their similar copies, present on the other homologous chromosome at the same loci. These two genes on the same locus always govern the same character.
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