Mendel is accredited as the first person to correctly understand the process of how characteristics are inherited by offspring from parents. Before Mendel many other incorrect hypotheses attempted to explain how characteristics and traits were passed from generation to generation, the most commonly accepted theory being the ‘blending theory’ which proposed that the traits of parents were blended together and an intermediate trait was expressed in the offspring. Mendel’s work on the common pea plant proved that was not the case.
Mendel performed a series of rigorous experiments that looked at 7 different characteristics (e.g. flower colour, seed color and seed shape), each with 2 different traits (e.g. purple flower and white flowers). He established true breeding lines for each characteristic. For example, one line of plants would produce only purple flowers and another only white. He then crossed individuals with two different traits to see the resulting trait of the offspring over three generations.
In his observations, Mendel found that in the first generation of offspring only one of the traits was ever expressed. After crossing the first generation of offspring with each other, Gregor Mendel found that approximately 75% of the second generation expressed the same trait as their parents (i.e. the first generation of offspring) and the remaining 25% expressed the second trait of the original parents, the trait that appeared to be lost in the first generation of offspring.
- Allele – a particular form of a gene. One allele is received from each parent
- Gamete – a reproductive cell containing half the genetic material of non-reproductive cells
Following three generations of cross-breeding Mendel produced three significant conclusions regarding genetic inheritance. His first conclusion was that each trait is passed on unchanged to offspring via ‘units of inheritance’. These units are now known as ‘alleles’. His second conclusion, offspring inherit one allele from each parent for each characteristic; and his final conclusion was that some alleles may not be expressed in an individual but can still be passed on to the next generation.
Mendel’s Laws of Inheritance
- Law of Segregation – The alleles for each character segregate during gamete production so that each gamete will only have one of the two alleles for each gene.
- Law of Independent Assortment – Pairs of alleles for each characteristic/gene segregate independently of each other.
Mendel’s work has been heavily built upon over the past 150 years and the field of genetics has come a long long way since his pea experiments. His work set the foundation for our understanding of how animals, plants and other complex organisms inherit traits from their ancestors. The process of inheritance is hugely important for understanding the complexity of life on Earth, in particular for its role in sexual reproduction and evolution. For this, Mendel’s contributions to science, biology and genetics are still widely recognized and applauded within the scientific community.
[p]Last edited: 24 May 2015[/p]