Question

What was Mendel's most important contribution to the modern understanding of biology?

• A. The concept of meiosis
• B. The concept of chromosome
• C. The concept that genes are ordered along chromosomes
• D. The concept that hereditary information comes in discrete units

Answer 1

The correct option is D The concept that hereditary information comes in discrete units

• Mendel observed that a cross between two pure breeding genotypes with contrasting character produces $F_1$ progeny which is not a blend of parental phenotypes but expresses phenotype of one parent. The heterozygous $F_1$ plant produces both parental phenotypes in offspring. This means that each character is governed by a pair of a discrete unit, called factor or genes which are similar in pure breeding genotypes. Mendel proposed the Law of segregation states that the two factors for a trait, present together in a heterozygous individual, do not get mixed and are separated during gametogenesis. Also known as the principle of purity as the segregation of two factors brings about the purity of gametes. But Mendel did not have any idea about the genetic basis of the law of segregation i.e. meiosis. The chromosomal theory of inheritance was proposed by Morgan which states that genes, the Mendelian factors, are present on chromosomes and homologous chromosomes separate during anaphase-I of meiosis resulting in segregation of alleles of a gene controlling the contrasting traits. The independent assortment of nonhomologous chromosomes during meiosis results in the independent assortment of two separate genes each of which carries an allelic pair. Thus the factor for two traits should be present on two different nonhomologous chromosomes to assort independently and to produce parental and nonparental combinations. Thus, the correct answer is option D.