Chromosomes: Structure and Discovery

Chromosomes: Structure and Discovery

Historical Observations of Chromosomes

Early studies of cell division in eukaryotes revealed threadlike structures within the nucleus, which became visible when stained with certain chemical dyes. These observations laid the foundation for understanding chromosomes and their role in cell division.

• Walther Flemming (1879): Used coal tar dyes to observe threadlike structures in dividing salamander embryo cells. He noted that these threads appeared in pairs before cell division and split into single threads in daughter cells.

• Term 'Mitosis': Flemming introduced the term mitosis (from Greek mitos, meaning 'thread') to describe the process of cell division involving these structures.

• Ascaris Studies: Research on the roundworm Ascaris showed that the number of threads (chromosomes) remained constant before and after mitotic division, indicating their stability during cell division.

Definition and Structure of Chromosomes

Chromosomes are highly organized structures composed of DNA and proteins, essential for the storage and transmission of genetic information.

• Wilhelm Waldeyer (1888): Coined the term chromosome ('colored-body') to describe these threadlike structures visible under a microscope.

• Chromosome Composition: Each chromosome consists of a single, long DNA double helix wrapped around proteins called histones.

• Organization: The DNA-histone complex forms a highly organized structure, facilitating efficient packaging and regulation of genetic material.

Key Terms

• Mitosis: The process of cell division resulting in two daughter cells with identical chromosome numbers.

• Chromosome: A threadlike structure composed of DNA and histone proteins, carrying genetic information.

• Histones: Proteins around which DNA is wrapped, aiding in chromosome organization and gene regulation.

Example

• During mitosis, chromosomes become visible as paired threads, which then separate to ensure each daughter cell receives an identical set of genetic material.

Additional info: Chromosomes play a central role in heredity, gene expression, and cellular function. Their discovery and structural elucidation were pivotal in advancing molecular biology and genetics.