CBSE - XII Science - Biology - Molecular Basis of Inheritance
where exactly is gene present on dna or on chromosome plz explain alongwith diagram and plzz explain in detail what is actually chromosomal theory of inheritance
- Genes are specific parts of chromosomes or deoxyribonucleic acid (DNA) segments found within the nuclei of cells in living organisms.
- They code for either a protein or RNA molecule and determine the hereditary characteristics.
Chromosomal theory of inheritance:
The chromosomal theory of inheritance was proposed independently by Walter Sutton and Theodore Boveri in 1902. They observed a closed similarity between the transmission of hereditary traits and the behaviour of chromosomes while passing from one generation to the next through male and female gametes. According to this theory chromosomes are the carriers of hereditary information. They possess Mendelian factors called genes. They segregate and assort independently during transmission from one generation to the next.
Chromosomes are the physical basis of heredity because they have a special organization, individuality, functions and capable of self duplication. They play a vital role in heredity, mutation, variation and evolutionary development of the species.
Salient features of chromosomal theory of inheritance:
- As the sperm and the egg cells serve as a connecting link from one generation to the other, all the hereditary characters must be carried in them.
- The hereditary factors are present in the nucleus of cells.
- Like Mendelian alleles, chromosomes are also found in pairs.
- The sperm and egg having haploid sets of chromosomes fuse to re-establish the diploid state.
- The genes are carried on the chromosomes.
- Homologous chromosomes synapse during meiosis and get separated to pass into different cells. This forms the basis of segregation and independent assortment.
- Genetic homogeneity and heterogeneity, dominance and recessiveness can be suggested by chromosomal type and behaviour.
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