The 19th century was an age of discovery, a time when stars rose and lit up the path ahead. Mendel was one of them; his observations regarding pea plants laid the foundations for genetic studies. The inheritance patterns he discovered were keys to brand new possibilities and understandings.
 
In order to better understand Mendel’s significance and contributions, one must go back to the year 1865. As an amateur biologist and monk, driven by his curiosity, Mendel initiated an observational study on pea plants. Throughout his years of endeavour, he observed a consistency of phenotypes on self-fertilized pea plants across generations. This type of self-fertilized plant is known as homozygous pure-breeders of the trait of interest. The plant itself has 2 identical alleles of the same gene, which will both contribute to a certain phenotype. This is the primary reason behind the consistency of phenotypes across generations of pure-breeders.
 
Before Mendel’s study, it was general believed that the offspring’s phenotypes are a blend of its parents’. However, Mendel’s results suggest otherwise. He cross bred the self-fertilized plants with smooth seeds and wrinkled seeds, and the result was not a pea plant with semi-wrinkle seeds but a pea plant with only smooth seeds. Cross breeding between 2 almost identical but slightly different species will result in offspring expressing one distinct phenotype inherited from one parent and repress the other distinct trait. This was later known as dominant and recessive gene, in which the offspring will inherit 2 distinct alleles of the same gene. One of the alleles will be expressive, known as the dominant allele, and the other not expressive known as the recessive allele. In the context of the pea experiment, the dominant allele is the one causing smooth seeds and the recessive is the one causing wrinkled seeds.
 
All the changes occur at the same gene with 2 different alleles, which is why diseases caused by such change are named monogenic disease or Mendelian disorder. Depending on whether the allele is dominant or recessive, a mutation is required to occur at 1 or both alleles in order to produce a disease. The inheritance pattern, based on Mendel’s theory, can be categorized into autosomal dominant or recessive, X-linked dominant or recessive, and Y-linked dominant or recessive. For example, mendelian disorders such as Huntington and Myotonic dystrophy are both autosomal dominant, which means that both diseases only require mutation in one of the alleles of the responsible gene located on non-sex chromosomes. Since both alleles are inherited but only 1 is expressive, researchers can look for common phenotypes between individuals identified with for example Huntington from the same family. By sequencing the human genome, researchers can more easily locate the problematic gene associated with the common phenotype and the monogenic disease. Mendel’s discoveries regarding dominant and recessive genes and inheritance patterns laid the foundation for understanding monogenic disorders. His ideas regarding inheritance patterns are critical in terms of understanding monogenic diseases and identifying the associated gene. Mendel’s ideas connected the dots between phenotype and disease, and even inspired people to look into more complicated polygenic diseases. Polygenic diseases are much more complicated in regards to monogenic diseases as they involve the “coordination” of several mutated genes. Mendel only looked into inheritance patterns of single genes. Genetics was non-existent during Mendel’s days, but his contributions did inspire people to investigate the “code” for inheritance. People started to map out the human genome in order to find out the problematic gene more easily. One of such projects is the “International HapMap Project”, which mapped out single nucleotide polymorphisms along every human chromosome. Researchers developed methods to analyze millions of SNPs at the same time. One of such methods is the PCR reaction, in which one’s DNA can be amplified and analyzed more easily. Once the problematic genes are identified, the mechanism and function each mutated gene serves in a polygenic disease can be understood better.
 
Just like how Darwin pioneered the field of biology, Mendel laid the foundations of modern genetics. This is where everything started. His major discoveries regarding inheritance patterns and dominant/recessive genes were the first instance in history that examines heredity in meticulous and specific details. The pea plantations in Mendel’s backyard was the anchor point, the bud at which modern genetics bloomed from. History was made when Mendel planted the first pea seed into the small pot of soil in his backyard.