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Mutations and Chromosomes - Chromosomes-Sex Determination

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Mutation is a sudden, heritable change in genotype that involves qualitative changed in genetic material. The change may lead to a corresponding change in the phenotype. The term mutation was coined by Hugo de Vries and is derived from the Latin word Mutare meaning 'to change'. A strain carrying such a change is called a mutant, and the process is called mutagenesis.

Mutations are extremely important source of genetic variability in living populations and are working tools for the geneticist in order to understand the structure and functioning of the gene. They are the deviations from normal genotypic and phenotypic conditions. The normal conditions are referred to as wild-type conditions. Mutations can occur either at chromosome level or at gene level. If the mutations occur at the chromosome level, they are called chromosomal aberrations or chromosomal mutations and if they occur at the level of gene they are called gene mutations.

Eukaryotic organisms have two primary cell types germ cells and somatic cells. Mutations can occur in either in cell type. If a germ altered in a germ cell, the mutation is termed a germinal mutation. Because germ cells give rise to gametes, some gametes carry the mutation and it will be passed on to the next generation. Typically germinal mutations are not expressed in the individual containing the mutation, but are expressed in the next generation.

Chromosomes-Sex Determination

The coloured thread like structures that appear during cell division have hidden within them all the secretes of genetic characters that are passed on from one generation to another generation. Hosing the particles of inheritance- the genes, these vehicles of heredity zre so important for all organisms because it is these that delimit one individual from another. These are the chromosomes ( Gr. Chromo: coloured; Soma: body). Which appear like coloured threads on staining.

It was waldeyer (1888) who first coined the term chromosome to the darkly staining bodies of the nucleus. Fleming(1879) actually had described the splitting of the chromosomes, but he had coined the term chromatin to refer to them. Sutton and Boveri(1902) suggested that the chromosomes are the carriers of hereditary particles. Morgan(1933) discovered the role of chromosomes in the transmission of hereditary characters. Hertz, kuwanda, geitter and Kaufmann have described the morphology of chromosomes.

Chromosomes occur as a network of fibrils called chromonema in the Interphase nucleus. At the time of cell division the chromonema breaks and condensation takes place forming specific number of chromosomes.

The number of chromosomes is constant for a given species. This number has been evolved during the course of evolution and characterizes the



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