CHAPTER_9 HEREDITY AND EVOLUTION Point to remember
GENETICS: The study of heredity and variation.
HEREDITY : The transmission of characters (or traits) from the parents to their offspring.
VARIATION: The differences in the characters among the individuals of a species.
CHROMOSOME: A thread like structure in the nucleus of cell formed of DNA and protein which carries the genes.
GENE: A unit of DNA or a segment of DNA which controls specific characteristic of an organism.
ALLELES: They are various forms of a gene which occur at the same particular position or locus over the chromosomes. DOMINANT GENE: The gene which decide the expression of a character even in the presence of an alternative gene.
RECESSIVE GENE: The gene which decides the expression of an organism in the presence of another identical gene. GENOTYPE: It is the description of genes present in an organism. PHENOTYPE: The characteristic which is visible in an organism.
F1 GENERATION: First filial generation – when two parents cross to produce progeny (offsprings) , then their progeny is called F1 generation.
HYBRID: A new form of plant resulting from a cross of different varieties of plants.
AUTOSOMES: The chromosomes except those involved in the determination of sex.
SEX-CHROMOSOME: The chromosomes which determine the sex of an individual.
FOSSILS: The remnants or impressions of organisms that lived in the remote past.
EVOLUTION: The sequence of gradual changes which take place in the primitive organisms over millions of years and result in formation of new species
PHYLOGENY: Evolutionary history of organism.
ONTOGENY: Developmental history of organism.
HOMOLOGOUS ORGANS: Organs which have the same basic structure and developmental origin but have different function and appearance. E.g. fore limb of a frog , a bird and a man.
ANALOGOUS ORGANS: Organs which have different basic structure and developmental origin but perform similar function. E.g. the wings of an insect and a bird.
VESTIGEAL ORGAN: Organs which are functionless and rudimentary in organisms but functional were in the ancestor. E.g. vermiform appendix, nictitating membrane.
BIOGENETIC LAW: It states that ―Ontogeny recapitulates phylogeny.‖ Genetic Drift: Random change in the frequency of genes in a population over successive generations.