Genetics defined as the science of heredity. 

Heredity is the transmission of traits from parents to offspring.

Gregor Mendel, an Austrian monk, was the first to study how traits pass from one generation to another.  He was born in 1822 in Brunn, Austria.  He studied science and mathematics at the University of Vienna, became a priest and worked as a substitute natural science teacher at a local technical school.  Mendel flanked twice in a qualifying examination for full time teachers.  But his failure to pass the examination led him to be one of the best biologists known today.  Mendel devoted more of his time tending the garden of monastery.  His passion in gardening was a great influence of his father who taught him about plants in the family’s orchard when he was young.  In 1856, at the age of 34, he began his plant breeding experiments in an Augustinian monastery.  In 1866, Mendel presented the result of his works to a group of scientists.  Unfortunately, no one understood his work.  Mendel died in 1884 and his work was buried with him.  It was not until 1900, that Mendel’s work was rediscovered, understood, and made known.  His experimental results laid the foundations of the basic genetic principles.  Due to his important contributions to the field, Mendel has become known as the Father of Genetics.

Mendel’s Experiments with Garden Peas

Mendel chose to work with the garden peas, because they are easy to cultivate and have a short generation time.  In addition, garden peas are self-pollinating, meaning the pollen grains are normally transferred to the stigma of the same flower, or the stigma of another flower in the same plant.  For experimental purposes, artificial cross-pollination (transfer of pollen from one plant to another plant) can also be easily performed.  This can be done by simple brushing the pollen from one flower on the stigma of another flower.

Mendel studied the inheritance of seven simple, distinguishable traits in garden peas, such as height, seed color, and so on…

As Mendel observed the inheritance of individual traits, he kept careful records of the number of offspring that expressed each characteristic.  In one of his experiments, he cross-bred a pure tall plant with a pure short plant which he called the P1 (first parental) generation.  A pure or pure-bred plant comes from a parent that always produces the same offspring through self-pollination.  Examples of these are the tall plants that always produce tall plants from generation to generation.  He transferred pollen grains from the anthers of tall plants to the stigmas of short plants to the stigma of tall plants.

At the end of the season, Mendel gathered the pea pods from these plants and planted the seeds.  When the seeds have grown and developed into maturity, he observed that the first filial (F1) generations were all tall.  Seemingly, the characteristic short had disappeared.  Mendel called the tall characteristic dominant because it seemed to dominate or mask the short characteristic.  He called the short characteristic recessive because it seemed to disappear in the offspring.  What happened to the short characteristic?

To find out, Mendel allowed the first generation offspring (F1) to self-pollinate and later planted their seeds.  At the end of the season, he was surprised to see that the “short” characteristic reappeared in the second filial generation of plants (F2).  When he counted the offspring the exhibited each characteristic, he found out that there were 787 tall plants and 277 short ones.  Mendel used his knowledge in mathematics to interpret the results.  He got a ratio that is very close to 3:1 (787/277 = 2.84/1).  This means that for every 3 tall plants, there is 1 short plant.

With repeated experiment using other traits, Mendel often got similar ratios.  Based on these observations, Mendel formed the following conclusions:

1.      If a pure-bred plant with the dominant characteristic were crossed with a pure-bred plant with recessive characteristic, all (100%) of the first generation offspring (F1) showed the dominant characteristic.

Example:

P1              pure tall   x   pure short

F1              all tall (100%)

2.      If the F1 generation were crossed, ¾ or 75% of the second generation offspring (F2) showed the dominant trait while ¼ or 25% showed the recessive trait.

Example:

P2              (from F1)         tall   x   tall

F2              3 tall   :   1 short

Related posts:

1. Genetics: Monohybrid Cross
2. Genetics: Genetics and the Laws of Probability
3. Genetics: Dihybrid Cross and the Law of Independent Assortment
4. Genetics: The Punnett Square
5. Living Things and the Environment