Notes on History of Genetics and Cytogenetics

1. History of Genetics and Cytogenetics

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Source: Principles of Genetics and Plant Breeding by BD Singh 

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History of Genetics and Cytogenetics:

• Genetics is the science of inheritance and variation.
• Genes are the functional units governing individual characteristics.
• Characters include morphological, anatomical, physiological, and behavioral features.
• Examples of human characters are eye color, hair color, blood groups, etc.
• Variation in characters indicates variation in the genes governing them.
• Cytogenetics studies chromosomes and their effects on organism development.
• Genes are universally accepted to be located in chromosomes.
• Cytogenetics originated by combining cytology and genetics.
• Cytology is the study of cell structures and functions.
• Genetics and cytogenetics are distinct grossly but not at the molecular level.

Spontaneous Generation:

• Organisms originate from pre-existing organisms of the same kind.
• Living organisms do not arise from nonliving matter.
• Spontaneous generation was believed by some biologists but refuted.
• Redi and Spallanzani presented evidence against spontaneous generation.
• Pasteur and Tyndall conclusively proved microbes do not originate spontaneously from organic matter.

Reproduction in Plants and Animals:

• Babylonians and Assyrians knew about pollination in palm trees.
• Eggs of birds were known, but mammalian eggs discovered later.
• De Graaf identified mammalian ovarian vesicles as eggs.
• Leeuwenhoek studied sperms but didn't speculate on fusion.
• Spallanzani proved sperm's essential role in progeny development.
• O. Hertwig provided conclusive proof of sperm-egg nucleus fusion.
• Thomas Fairchild produced the first artificial plant hybrids in 1717.
• Linnaeus, Koelreuter, and Gaertner produced artificial plant hybrids.
• Amici described pollen tube entry into the ovary.
• Strausberger described fertilization in angiosperms in 1884.

Preformation:

• Heredity debate about the contribution of male and female parents.
• Aristotle believed progeny form came from semen, substance from females.
• Animalculists and ovists developed these concepts further.
• Some claimed to see "homunculus" in human sperms.
• Preformationists believed miniature human beings were in gametes.
• Preformationists thought progeny developed from preexisting beings.
• Improved microscopes challenged the idea of preformation.
• Epigenesis replaced preformation as the accepted view.

Epigenesis:

• Organs and tissues of adults develop from uniform embryonic tissues.
• Differentiation from homogeneous embryonic tissues leads to organs.
• Wolff proposed epigenesis but believed adult tissues originated de novo.
• Von Baer suggested that adult tissues developed from embryonic tissues.
• Von Baer's concept is the universally accepted view of organ development.

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