Have you ever wondered why children look like their parents? Why does your great aunt say that you have your mother's eyes? And why were you the one to end up with your grandfather's red hair and green eyes? These are common questions readily answered today, but were first correctly answered by a monk in the 1800's who laid the foundations of the modern science of genetics.
Johann Gregor Mendel was born the son of Anton and Rosine Mendel on July 22, 1822 in Heinzendorf (present day Czechoslovakia). He was born into a family of Moravian peasants and proved to be very talented. With the help from his parents and private tutoring, he was able to obtain further education. With the limited financial resources offered by his parents, he attended the Gymnasium in Opava. Mendel was forced to provide for himself in 1838, due to his father's debilitating farming accident. In 1840, he attended a two-year course at the Philosophy Institute at Olomouc University. Once again, Mendel struggled for money, but was indebted to his younger sister for renouncing part of her dowry to finance his studies. At the age of twenty-one, Mendel entered the Brno monastery, which would become "his only chance of realizing his intellectual ambitions" (Orel, 1984, p.23). Fr. Matthaeus Klacel, a botanist who was regarded as an expert in natural sciences (also engaging in crossing plants), became his mentor. Mendel spent a short time as chaplain at a nearby hospital, until 1849 when he taught mathematics and classics at the Gymnasium in Znojmo. A year later, Mendel failed his teacher's examinations at Vienna University due to his weakness in zoology. During a professor's illness in 1851, he taught natural history at the Technical College. Later that same year, he studied physics at Vienna University, where he gained the empirical, methodological, and scientific knowledge that would eventually prepare him for his future research with plants. Even after his studies at Vienna, he once again failed the teacher's examinations in 1856. But Mendel would not give up easily. His interest in growing plants led him to conduct numerous experiments on plant hybridization, which eventually led to his theories surrounding the science of heredity. He reported on his plant hybrid experiments to the Brunn Natural Science Society in 1865 and had his paper on this topic published a year later. In 1868 Mendel was elected abbot of the monastery and also vice president of the Natural Science Society. In the following year, he conducted more experiments with different plant species and reported his findings to the Society. Before his death in 1884, Gregor Mendel continued research, held positions in many organizations, and was nominated for many honors. Although Mendel's research is very well known today, it took thirty-four years for the science community of the time to realize it's importance (Stern, 1966).
The naturalists of the middle nineteenth-century believed that everything in nature could be explained scientifically. Mendel sought to apply this belief to the study of heredity. His research methods consisted of three clearly defined steps. First he devised a series of experiments with pea plants to examine the basis for heredity. Next he observed the results of breeding as reproduction to the highest laws, from which lower laws could be deduced. Finally, he used statistical principles to interpret his results, which was something that set Mendel apart from the other experimenters of the day.
After 1850, naturalists were experimenting with plant hybridization and Mendel was aware of and acquainted with the controversy over generation and fertilization at the time. He reviewed C.F. Gartner's research on plant hybridization (1849), along with Unger's lectures in 1851 about botanical research. Mendel's goal, however, was to explain the law of the development and origin of hybrids, being fully aware of the difficulty of the task and the mystery of heredity (Orel, 1984).
Mendel's Pisum experiments involved crossing and testing a large quantity of selected plants. Between 1854 and 1863, he studied nearly 28,000 plants. His aim was to examine how the plant's characters were passed on from generation to the next. The plants of genus Pisum have quite distinct characters in seeds and in plants that are easily distinguishable and they yield perfectly fertile hybrids. In Mendel's terms, a hybrid is the product of the first crossing, or the F1 generation (Orel, 1984).
In his first experiment, Mendel crossed a purebred round seed with a purebred angular seed and the result was that all of the hybrids were round. They acquired the shape from the round-seeded parent. He then planted the round hybrid seeds which self-fertilized (became the F2 generation), which resulted in 5,474 round seeds compared to 1,850 angular seeds. From this finding, Mendel concluded that the characters segregate in a ratio of 3:1. Because the round-seeded hybrids prevailed over the angular-seeded hybrids, the round trait is known as dominant, while the angular trait is the recessive. This finding rejects the notion of blended inheritance. Mendel continued his experiments in subsequent generations (to four generations), which other naturalists have never considered (Orel, 1984).
Gregor Mendel's experiments with plant hybridization gave way to what is now known as the Mendelian Theory in modern genetics. This theory states that an individual has two genes, factors that determine the hereditary transmission of characters, for each character. The two genes may be the same or different. The different genes are called alleles. Mendel's experiments revealed the existence of dominant allele (A) and recessive (a). The parent plants are the (A) and (a) alleles, which form the hybrid (Aa). The (A) is the dominant allele, so (AA) and (Aa) would both exhibit the dominant trait(Mendel, 1950). The test cross method, developed by Mendel, is a useful tool in predicting the genotype of an organism. In today's terminology, a homozygous dominant trait (AA) is crossed with a homozygous recessive trait (aa) to yield four heterozygotes, each with the only A genotype expressed.
After 1900, Pisum experiments were conducted in England confirming Mendel's findings. Mendel is credited with the fundamental discovery of the physical unit of heredity. He has been described as "giving birth" to an entirely new theory, laying the foundation for a completely new line of research (Orel, 1984, p.72).