Mendel’s work in genetics - SS3 Biology Lesson Note

Gregor Mendel, an Austrian monk, and botanist, is considered the father of modern genetics. His pioneering work laid the foundation for understanding the principles of inheritance and the transmission of traits. Mendel conducted his experiments on pea plants (Pisum sativum) in the mid-19th century and established three key principles of heredity, which are now known as Mendel's laws or Mendelian inheritance.

1.       Law of Segregation: Mendel proposed that hereditary traits are determined by discrete units of inheritance, which we now call genes. He observed that for each trait, an organism possesses two copies of the gene, one inherited from each parent. These copies are called alleles. Mendel's law of segregation states that during the formation of reproductive cells (gametes), the two alleles for a trait segregate and only one allele is passed on to each offspring. This segregation occurs randomly and independently for different traits.

2.       Law of Independent Assortment: Mendel also discovered that the inheritance of different traits is independent of each other. In other words, the alleles for one trait segregate independently of the alleles for another trait during gamete formation. This principle is known as the law of independent assortment. However, this principle only holds true for genes that are located on different chromosomes or are far apart on the same chromosome. Genes that are closer together on the same chromosome tend to be inherited together, a phenomenon known as genetic linkage.

3.       Law of Dominance: Mendel observed that some alleles are dominant over others in their expression. When an organism carries two different alleles for a trait (heterozygous), the dominant allele is expressed, while the recessive allele remains hidden. Only when an organism carries two copies of the recessive allele (homozygous recessive) will the recessive trait be observed.

Mendel's laws of inheritance provided a framework for understanding the patterns of genetic inheritance. Although his work went unrecognized during his lifetime, it was rediscovered and widely recognized in the early 20th century, laying the groundwork for modern genetics and the study of inheritance patterns in various organisms, including humans.