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Standard XII
Biology
Question

Chromosome theory of heredity was formulated for the first time on the basis of which of the following observation?
  1. Chromosomes being main structure in nucleus.
  2. Chromosomes exhibiting segregation and independent assortment during meiosis.
  3. Determination of sex through sex chromosomes.
  4. A fixed number of chromosomes in each cell of an organism.

A
Chromosomes being main structure in nucleus.
B
Determination of sex through sex chromosomes.
C
Chromosomes exhibiting segregation and independent assortment during meiosis.
D
A fixed number of chromosomes in each cell of an organism.
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Solution
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Sutton recognized inheritance of Mendal’s factors and behavior of chromosome in meiosis and fertilization. He observed that both chromosomes and alleles of each gene are present in pairs which are separated and delivered singly to gamete during meiosis. Separation of two non homologous pairs of chromosomes and gamete formation is independent of each other as is the independent assortment of alleles of different genes in Mendel’s dihybrid cross. During fertilization one member of homologous pair of chromosome is derived from male parent and other from female parent as do the two alleles of a gene. This makes option A correct.

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Q1
Chromosome theory of heredity was formulated for the first time on the basis of following observation
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Q2

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Q3
Consider the following statements.
A. Law of dominance, law of segregation and law of independent assortment etc. are the Mendelian principles.
B. Recombination in the progeny level results due to crossing over of chromosomes in meiosis.
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D. X-Y mechanism of sex determination is seen in human beings.
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Q4
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Q5

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