How We Became What We Are

Introduction to Genetics

Genetics is the study of variations and how they are transferred from one generation to another.

Gregor Johann Mendel is considered to be the father of genetics. During his time, his findings were not accepted, but later in 1900, three scientists DeVries, Correns, and Tschermak rediscovered Mendel’s work.

The term genetics was coined by W. Batson in 1905.

Now let us explore some of the terms related to the study of genetics.

• Heredity − It is the transmission of traits from one generation to the other generation.

• Variation − It can be defined as the difference observed among members of the same species and also among offsprings of the same parent.

• Gene − A gene is the unit of inheritance, which is transferred from the parent to the offspring. It controls the expression of a character. A gene is a linear piece of DNA which is present in nucleus.

• Allelomorphs − Every character is controlled by two genes, which control contrasting expressions. A pair of genes that controls the contrasting characters and lies on the same loci in the homologous chromosomes is called an allele.

• Dominant allele − An allele which expresses itself in the presence of its contrasting allele is called a dominant allele.For example, the character tallness is determined by two alleles T and t, where T is the dominant allele and t is the recessive allele. In the presence of T, the expression of t does not occur.

• Recessive allele − The allele which cannot express itself in the presence of the dominant allele is called a recessive allele.

• Homozygous organism − In an individual, if the alleles of a character are similar, then they are known as homozygous. For example, TT is a homozygous condition.

• Heterozygous organisms − If the alleles of a character are dissimilar, then they are called heterozygous. For example, Tt is a heterozygous condition.

• Phenotype − It is the physical expression of a character. E.g., tall plant

• Genotype − It represents how an organism is genetically made up. For e.g., TT or Tt or tt

• F₁ generation − It is the first filial generation which is produced when two pure parents are crossed. For example, the F₁generation produced when two pure line plants TT and t…