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Genetic Terminology, , , , » Genetics is the branch of science which deals with heredity and variation in living, organisms. The term genetics was coined by W.Bateson., , >» Phenotype: The physical appearance of a genetic trait that results from a specific, genotype, , » Genotype: The genetic constitution of an organism, , >» Homologous Chromosomes: Chromosomes which are identical in size, structure and, behaviour. These chromosomes occur in pairs in haploid cells. In a homologous pair, one is maternal and the other is paternal., , >» Haploid: A cell or individual with one copy of each chromosome., , > Diploid: A eukaryotic cell or organism with two complete sets of chromosomes. This is, double the haploid chromosome number., , >» Gene:, , >» Gene is the fundamental unit of chromosome., , >» Genes determine the traits or characters of the organisms., , » It is a nucleotide sequence that specifies the sequence of amino acids in a, polypeptide., , >» The specific place on a chromosome where a gene is located is called locus., , >» The term gene was coined by W.L.Johansen., , > Alleles:, , > Alternative forms of a gene are called alleles., , > Alleles are formed due to mutations., , >» They are present at same place on homologous chromosomes., , > For example, T and t alleles respectively specify tallness and dwarfness of the pea, plant., , » The term allele was coined by Bateson., , » Homozygous :, , » Homozygous refers to a particular gene that has identical alleles at a given locus on both, homologous chromosomes., , >» For a dominant trait it is referred with two capital letters TT, and two lowercase letters tt, for a, recessive trait., , » Heterozygous:, , >» Heterozygous refers to a particular gene that has two different alleles at a given locus on both, homologous chromosomes., , >» For example, Fl monohybrid plants Tt, , >» Dominant allele:, , > The allele which is expressed in both homozygous and heterozygous conditions is called, dominant allele., , >» Dominant alleles are represented with capital letters., , > Recessive alleles:, , » The allele which is expressed only in homozygous condition and unable to express in, heterozygous condition is called recessive allele., , » Recessive alleles are represented with small letter of corresponding alphabet., , > Genome:, > The haploid set of chromosomes present in a gamete or a cell is called genome., > Genome contains all the information required to build and maintain the organism., , > Punnet Square:, > It is gametic checker board used to show the result of a cross between two, , organisms., > It was formulated by Reginald C Punnet in 1927.