Walther Flemming was the first scientist to identify and describe chromosomes in 1879. Walther Flemming was a renowned German biologist and the pioneer of the branch of cytogenetics. {1}
In this article, we explore the history of the discovery of chromosomes, from the earliest microscopes to the development of the chromosome theory.
The Advent of Cell Theory
The advent of cell theory was a pivotal moment in the history of biology. It was a revolutionary concept that stated that all living organisms are made up of cells, which are the basic units of life.
This theory was first proposed in the mid-19th century by scientists such as Matthias Schleiden and Theodor Schwann. They observed that cells are the fundamental building blocks of all living things and that all cells arise from pre-existing cells.
The advent of cell theory helped to establish biology as a distinct scientific discipline and has had a profound impact on our understanding of the nature of life and its processes.
Who Discovered Chromosomes?
Walther Flemming, a renowned German biologist and the pioneer of the branch of cytogenetics, was the first scientist to discover chromosomes. {1}
He observed the behavior of chromosomes during cell division using a staining technique that made the chromosomes visible under the microscope. An important point to note here is that although Walther Flemming identified the chromosomes, he had initially named the fibrous network inside the nucleus as “chromatin” (which means stainable material).
But it wasn’t until 1888, that Heinrich Waldeyer, a German anatomist coined the term “chromosome.” {2}
Walther Flemming, known for his attention to detail, not only identified the chromosomes within the nucleus, but also explained several other aspects of cell division, which were later confirmed by studying live cells under the microscope. Some of these observations include:
- Chromosomes split along their length during mitosis
- The split chromosomes divide into distinct daughter cells at the end of mitosis
- The cell divides into daughter cells over multiple stages — prophase, anaphase, metaphase, and telophase
Walther Flemming’s research and detailed descriptions on the mechanisms of cell division were vital in the discovery of hereditary mechanisms.
The Contribution of Other Scientists to Chromosomal Studies
Cytogenetics is the study of chromosomes, their structure, function, and behavior in cells. It is a branch of genetics that focuses on the study of the physical and chemical properties of chromosomes and their relationship with genes and DNA.
The history of cytogenetics dates back to the late 1800s when the first observations of chromosomes were made. Since then, several scientists have contributed to the field, including Theodor Boveri, Walter Sutton, Thomas Hunt Morgan, and Barbara McClintock, among others.
After Walther Flemming’s discovery, in 1887, Eduard Strasburger, a Polish botanist, was the first to describe the process of meiosis, which is the cell division that produces gametes (sex cells). He observed that during meiosis, chromosomes would come in pairs, separate, and then move to opposite poles of the cell.
In 1890, August Weismann, a German biologist, proposed the germ-plasm theory, which suggested that only germ cells, or cells that produce sex cells, could transmit genetic information from one generation to the next. He also proposed that the chromosomes carry genetic information. {8}
In 1902, Theodor Boveri, a German biologist, conducted experiments on sea urchin eggs, in which he observed abnormal cell division and embryo development. Boveri concluded that chromosomes carry the genetic information. {9}
In 1903, Walter Sutton, an American geneticist, independently proposed the chromosome theory of inheritance, which suggested that genes are located on chromosomes and that the behavior of chromosomes during cell division explains the transmission of genetic traits from one generation to the next. {10}
In 1910, Thomas Hunt Morgan, an American geneticist, conducted experiments on fruit flies in which he observed that mutations could be linked to specific chromosomes. He also observed that genes located on the same chromosome tend to be inherited together, which he called genetic linkage. Morgan’s work provided evidence to support the chromosome theory of inheritance. {11}
In 1928, Fred Griffith, a British bacteriologist, discovered the process of transformation in bacteria, in which genetic material could be transferred from one bacterium to another. {12} Griffith’s work further supported widely held views that genetic material was responsible for the inheritance of traits and paved the way for future studies on DNA.
In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty, American scientists, conducted experiments in which they identified DNA as the genetic material responsible for the inheritance of traits. They used bacteria to show that when DNA was destroyed, the bacteria lost their ability to produce a particular trait, while destroying other cellular components had no effect on the trait. {13}
In 1953, James Watson and Francis Crick, American and British scientists, respectively, proposed the double-helix model of DNA. Their model explained how DNA could store genetic information and be replicated during cell division. Watson and Crick’s work paved the way for future studies on the structure and function of DNA. {14}
In 1983, Barbara McClintock, an American geneticist, was awarded the Nobel Prize in Physiology or Medicine for her discovery of transposable genetic elements or “jumping genes” in corn. {15}
McClintock’s work challenged the traditional view of genetic inheritance and showed that genes can move around within chromosomes, leading to changes in gene expression and potentially new traits.
Modern Techniques in Chromosome Studies
The study of cytogenetics has continued to evolve and expand since the early discoveries of Flemming and other scientists. Today, researchers in cytogenetics use advanced technologies such as karyotyping, fluorescent in situ hybridization (FISH), and comparative genomic hybridization (CGH) to determine how many chromosomes cells have, and study the structure, function, and behavior of chromosomes and DNA.
Frequently Asked Questions
Sources:
1 – National Human Genome Research Institute: “1879: Mitosis Observed.”
2 – Genomic Research: “Genomic Structure and Evolution of the Ancestral Chromosome Fusion Site in 2q13–2q14.1 and Paralogous Regions on Other Human Chromosomes.”
3 – National Human Genome Research Institute: “1902: Chromosome Theory of Heredity.”
4 – Human Genetics: “The discovery of the human chromosome number in Lund, 1955-1956.”
5 – Proceedings of the Royal Society, Biological Sciences: “Sex chromosome evolution: historical insights and future perspectives.”
6 – Biomedical Journal of Scientific and Technical Research: “History of The Research on Sex Determination.”
7 – Arizona State University: “Sex Determination in Humans.”
8 – Arizona State University: “The Germ-Plasm: a Theory of Heredity (1893), by August Weismann.”
9 – Arizona State University: “Theodor Heinrich Boveri (1862-1915).”
10 – Arizona State University: “Walter Stanborough Sutton (1877-1916).”
11 – Genetics: “2010: A Century of Drosophila Genetics Through the Prism of the white Gene.”
12 – Genome Biology: “Transformation.”
13 – National Human Genome Research Institute: “1944: DNA is “Transforming Principle”.”
14 – National Library of Medicine: “The Discovery of the Double Helix, 1951-1953.”
15 – Arizona State University: “Barbara McClintock’s Transposon Experiments in Maize (1931–1951).”