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  Section: Genetics » Physical Basis of Heredity » The Nucleus and the Chromosome
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Significance of nucleus : Hammerling's experiment

Physical Basis of Heredity 1.  The Nucleus and the Chromosome
The Nucleus 
Significance of nucleus : Hammerling's experiment
Number, shape and size of nucleus
Nucleus in prokaryotes and eukaryotes
Nuclear envelope
Nuclear pore complex and nucleocytoplasmic traffic
Number, size and shape of chromosomes
Morphology of chromosomes
Euchromatin and heterochromatin
Constitutive and facultative heterochromatin
Single-stranded and multi-stranded hypotheses for chromosomes
Chemical composition of chromosomes
Infrastructure of chromosomes
Function of chromosomes
Special types of chromosomes 
Lampbrush chromosomes
Salivary gland chromosomes
Prokaryotic Nucleoids

Hammerling's experiment
J. Hammerling, a German biologist, demonstrated in 1934 that the nucleus determines the characters of the cell and ultimately the characters of the individual. He conducted certain experiments using two species of a green alga, Acetabularia. The two species, namely A. crenulata and A. mediterranea used in this experiment differ in the shape of their caps. While in A. crenulata the cap has loose rays, in A. mediterranea an umbrella-like cap is found. The nucleus in both the species is situated in rhizoid at the bottom of stalk. If cap is cut off, it will develop again and its shape will be that of the original type. However, if after removing the caps, stalk of one species, is grafted on rhizoid (containing the nucleus) of the other species, shape of cap will be determined by nucleus and not by stalk (Fig. 6.1). If the nucleus belongs to A. crenulata, shape of cap will be of the crenulata type and if the nucleus comes from A, mediterranea, cap will be of mediterranea type. When both nuclei are present, shape of cap will be intermediate. This experiment demonstrated clearly that characters of an individual are controlled by nucleus of the cell or cells.
Hammerling's experiment in Acetabularia showing relative roles of nucleus and cytoplasm (redrawn from Swanson : The Cell).
Fig. 6.1. Hammerling's experiment in Acetabularia showing relative roles of nucleus and cytoplasm (redrawn from Swanson : The Cell).


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