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Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

Bihar BoardEnglish MediumSTD 12 ScienceBIOLOGYPrinciples of Inheritance and Variation5 Marks
Question
Explain the chromosomal theory of inheritance.
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Answer

Chromosomal Theory of Inheritance:
The chromosomal theory of inheritance was proposed independently by Walter Sutton and Theodore Boveri in 1902. According to this theory,
  1. Since the sperm and egg cells provide the only bridge from one generation to the other, all hereditary characters must be carried in them. ii. The hereditary factors are carried in the nucleus.
  2. Like the Mendelian alleles, chromosomes are also found in pairs.
  3. The sperm and egg having haploid sets of chromosomes fuse to re-establish the diploid state.
  4. The genes are located on the chromosomes in a linear order. As there are two chromosomes of each kind in somatic (diploid) cell there must be two genes of each kind, one in each of the two homologous chromosomes.
  5. Homologous chromosomes synapse during meiosis and get separated to pass into different cells. This forms the basis for segregation and independent assortment. A gamete receives only one chromosome of each type and thus has only one gene for a trait. The paired condition is restored by fusion of gametes.

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