DECODE The Script of LIFE

     Genes are the fundamental units of heredity, acting as the instructions for the synthesis of proteins that perform a multitude of functions within living organisms. Each gene is a segment of DNA located on chromosomes, carrying the code that dictates specific traits or functions. For instance, the gene for eye color contains the blueprint for the production of pigments that give our eyes their distinctive hues, such as blue, brown, or green.     A lleles, on the other hand, are different versions of the same gene that arise due to variations in the DNA sequence at a particular locus on a chromosome. These variations lead to the diversity of traits observed within a species. A single gene for hair color, for example, may have multiple alleles corresponding to black, brown, blonde, or red hair. Similarly, the gene determining blood type possesses alleles A, B, and O, each contributing to the blood type of an individual.      The expression of these alleles can be either dominant o

  Sex Determination Mechanism Finalization of sex at the time of zygote formation is called sex determination. Two types of chromosomes are present in individuals – sex chromosomes (which determine the sex of individuals) and autosomes. 1. XX-XY TYPE Seen in many insects and mammals including humans, Drosophila melanogaster. Males have X and Y chromosomes along with autosomes [A] and females have a pair of X chromosomes. 2. XX-XO TYPE Seen in grasshopper. Males have only one X chromosomes besides autosomes and females have a pair of X chromosomes. 3. ZZ-ZW TYPE Seen in birds, fowl and fishes. Females have one Z and one W chromosomes whereas males have a pair of Z chromosomes. 4. XX-XY TYPE Seen in cockroaches. Females have only one Z chromosomes besides autosomes and males have a pair of Z chromosomes.

  Mendel’s Laws of Inheritance Gregor Johann Mendel (1822–1884) is known as “Father of Genetics”. In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants. He called genes as “factors”, which are passed from parents to offspring’s. Genes, that code for a pair of opposite traits are called “alleles”. He conducted artificial pollination / cross-pollination experiments using several true-breeding varieties having contrasting traits. Mendel’s Experimental Plant Mendel selected garden pea as his experimental material. Phenotype: Visible expression of genetic constitution e.g., Tall/dwarf Genotype: Genetic constitution of individual e.g., TT, Tt, tt. Mendel’s Observations Monohybrid Cross: Cross involving study of inheritance of one character, e.g., height of plant. Dihybrid Cross: Cross between plants differing in two traits/cross involving study of inheritance of 2 genes or characters. Homozygous: The individual carrying similar alleles for a trait e.g., TT or