sábado, 16 de febrero de 2019

Chromosome History

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By Ananya Mandal, MDReviewed by Sally Robertson, B.Sc.

The scientific field of genetics first began with the research conducted by Gregor Mendel, who is known of as the "Father of Genetics". Mendel performed extensive experiments with pea plants to demonstrate that characteristic traits inherited by the plants followed certain patterns, patterns which are today known of as the laws of Mendelian inheritance. Mendel's research involved thousands of pea plants which he studied over an 8 year period in the mid 19th century.

It was in 1866 that Ernst Haeckel first described the nucleus as the centre for passing on elements that determine hereditary characteristics in his work, "Generelle Morphologie". Almost two decades later, German scientist August Weismann found that gametes or sperm and egg cells were different from somatic or body cells. He also suggested that the nucleus is the centre where the genetic material that is responsible for heredity lies. He added that when the sperm and the egg join in fertilization, a new combination of chromosomes is formed. The cell division process (meiosis) that produces gametes containing 23 chromosomes, was first described by Eduoard van Beneden.

Theodor Boveri described two important properties of chromosomes contained within the nucleus. One of these was the uniqueness of each chromosome and the other their potential for passing on chromosomal information through generations. Wilhelm Roux had previously suggested that each chromosome was unique, but it was Boveri who managed to prove this fact in his experiments.

The work of Mendel was rediscovered and promoted around this time (1902) by Boveri who found the connection between the laws of Mendelian inheritance and chromosomal behaviour. Boveri's colleagues were American cytologists Edmund Beecher Wilson, Walter Sutton and Theophilus Painter. The chromosomal maps came later from the labs of T.H. Morgan.

Chronological order of events in genetics and chromosomal research

1860s: Mendel proposed laws of inheritance that are independent of gametes
1875: The process of cell division in somatic cells or mitosis was discovered
1890: The process of reduction cell division in formation of gametes or meiosis was discovered
1900: Mendel is rediscovered by botanists Correns, de Vries, and von Seysenegg independently
1902: The laws of inheritance and behaviour of chromosomes are found to be parallel as noted by Walter Sutton, Theodor Boveri and others. They noted that chromosomes are paired in somatic cells, that reduction division or meiosis occurs within gametes, and finally that fertilization restores the paired status of chromosomes.
Early 1900s - Thomas Hunt Morgan from Columbia University confirms the presence of Mendel's inherited factors on chromosomes from Drosophila melanogaster or fruit flies. He also found sex chromosomes and sex linked diseases and traits.