“A chip of the old block”, and “Like father, like son” are some of the age old adages that reflect man’s understanding of resemblances in families, especially between parents and children. There has always been a general acceptance that “like begets like”. Interestingly much support and study to highlight this fact was Gregor Mendel’s outstanding contributions to the field of genetics.
Gregor Mendel, an Austrian monk who lived from 1822-1884 , spent eight years working on pea plants, observing their physical properties, especially the color of the flowers. He was literally fascinated by the subject, that the final outcome was the presentation of his three famous laws of inheritance known today as the Mendelian Laws of Inheritance.
Chromosomes are the basic units of hereditary. They consist of genes, the carriers of the many traits in any living thing. Genes exist in pairs. Each odd is called an allele. Chromosomes have gene pairs which separate during the formation of the two gametes. Mendel’s studies were based on the fusion of the pollen with the ovule (each with one set of alleles) of pea plants of differing traits.
Allele: One form of a gene / trait
Dominant: An expressive allele in a gene pair, suppressing the trait of the second allele
Recessive: An allele in a gene pair which is hidden, or trait suppressed by a dominant one.
Gamete: A reproductive cell after the division or split of the sex cell. Generally, in plants, it is the pollen and the ovule, while in animals it is the sperm and the egg.
Homozygous: A pair of identical alleles
Heterozygous: Each allele in a gene pair with dissimilar traits
#1. Law of Segregation:
This law states that genes segregate during gamete formation into their different alleles. During fertilization of gametes, each allele pairs with a new allele. However, each allele remains unaltered from generation to generation.
Suppose that in a red pea plant, the two alleles for the trait red are characterized by both alleles being red. When the chromosome splits during gamete formation, each allele will carry the trait for red. This trait red for that allele remains unchanged even if the gamete fuses with a gamete carrying white trait and the allele is transferred to the subsequent generations in this unaltered state.
#2. Law of Independent Assortment:
This law states that a living being contains many kinds of traits or many kinds of genes. These genes exist in pairs and the splitting of the genes into alleles is independent, one from the other. It means to say that in a pea plant, for example, the traits for color, lengths or shape of the pea pod are all independent of each other and do not influence the inheritance patterns of each other.
# 3. Law of Dominance:
Genes exist in allele pairs being either heterozygous or homozygous. In a homozygous pair of alleles, the character trait is not affected by change or a mix of traits, while in a heterozygous combination, the character of one trait is exhibited (dominant) while the other trait of the gene pair is hidden (recessive).
During Mendel’s experiment, when the gamete for pure red flower (RR) was fused with the gamete for pure white flower (rr), there resulted four possible combinations; all exhibited as Rr. The color of the flower Rr was observed as Red, indicating the allele for white(r) was masked or hidden by the dominant allele red (R).
In an experiment conducted for fusing mixed bred gametes for red and white flowers , all gametes indicated as (Rr), the result was a 75 % red while only 25% turned out to be with white flowers.
Rr X Rx = RR + Rr +Rr + rr
RR and Rr = Red
Rr = white
Mendel’s Laws of inheritance were able to set the basis for understanding the basic or outlining principles of inheritance and were also able to help make predictions of genetic traits in off-springs. These laws also help explain character traits such as color of the eye (how blue is a result of two recessive genes) and sickle cell anemia, to name a few. Exceptions to these laws are those that are found in genetic anomalies such as Down’s Syndrome. Apart from that, most living things around us follow the three Laws of Inheritance.
So profound was the work of Mendel that affected the study of genetics following his death, that he came to be known as the Father of Genetics. T. H Morgan’s famous experiments on the fruit fly (Drosophila melanogaster) were based on these genetic discoveries by Mendel.