Controversies Did Mendel articulate the laws of inheritance attributed to him? The two laws of inheritance most often attributed to Mendel are segregation and independen assortment 1. The law of segregation, stated in modern terms, is that during meiosis two alleles of a single locus, one inherited from each parent pair with each other, and then segregate from one another into the germ cells so that each germ cell carries only one allele of that locus. Segregation in heterozygous individuals produces in equal proportions two different types of gametes, each with one of the two alleles 2. The law of independent assortment, stated in modern terms, is that the segregation of alleles of a single locus has no influence on the segregation of alleles at another locus. The result is completely random and uniform combinations of alleles of different loci in the self-fertilized progeny of dihybrid (or multihybrid )individuals The law ofsegregation: Genetic terms, such as allele, locus, and chromosome, had not been coined in Mendel's day nor was the cellular process of meiosis understood Mendel referred to segregation of hereditary elements several times in his paper. He concluded: .the differing elements succeed in escaping from the enforced association only at the stage at which the reproductive cells develop. In the forma f these cells, all elements present participate in completely free and uniform fashion, and only those that differ separate from each other. In this manner the production of as many kinds of germinal and pollen cells would be possible as there are combinations of potentially formative elements This paragraph, however, is a remarkably lucid summary of the law of segregation o Mendel's reference to"potentially formative elements" implies the existence of invisible particulate determinants of inherited traits. We might well view the term"element, he equivalent of the modern term"allele o Mendel's reference to the "enforced association"of differing elements indicates that he perceived the differing elements as being paired in hybrids(heterozygotes) o His statement that differing elements "separate from each other"shows a clear understanding of segregation that is similar to the modern view o He also correctly recognized that segregation takes place "only at the stage at which the reproductive cells develop"(i.e, during meiosis) This paragraph, however, reveals one aspect of Mendel's perception that differs from the modern concept of segregation o Mendel perceived segregation as an anomaly restricted to hybrids(heterozygotes) o He called the differing elements"antagonistic elements"whose association in the hybrid is a"compromise, and wrote that only those elements that differ separate from one Mendel represented heterozygotes with a two-letter designation(Aa), as modern geneticists usually represent them, he consistently represented homozygotes with a single letter (A or a rather than the two letters(Aa or aa) used todayControversies 4 Did Mendel articulate the laws of inheritance attributed to him? The two laws of inheritance most often attributed to Mendel are segregation and independent assortment. 1. The law of segregation,stated in modern terms, is that during meiosis two alleles of a single locus, one inherited from each parent, pair with each other, and then segregate from one another into the germ cells so that each germ cell carries only one allele of that locus. Segregation in heterozygous individuals produces in equal proportions two different types of gametes, each with one of the two alleles. 2. The law of independent assortment, stated in modern terms, is that the segregation of alleles of a single locus has no influence on the segregation of alleles at another locus. The result is completely random and uniform combinations of alleles of different loci in the self-fertilized progeny of dihybrid (or multihybrid) individuals. The law of segregation: Genetic terms, such as allele, locus, and chromosome, had not been coined in Mendel's day, nor was the cellular process of meiosis understood. Mendel referred to segregation of hereditary elements several times in his paper. He concluded: • “the differing elements succeed in escaping from the enforced association only at the stage at which the reproductive cells develop. In the formation of these cells, all elements present participate in completely free and uniform fashion, and only those that differ separate from each other. In this manner the production of as many kinds of germinal and pollen cells would be possible as there are combinations of potentially formative elements.” This paragraph, however, is a remarkably lucid summary of the law of segregation. o Mendel's reference to "potentially formative elements” implies the existence of invisible particulate determinants of inherited traits. We might well view the term "element,” as the equivalent of the modern term "allele." o Mendel's reference to the "enforced association" of differing elements indicates that he perceived the differing elements as being paired in hybrids (heterozygotes). o His statement that differing elements "separate from each other" shows a clear understanding of segregation that is similar to the modern view. o He also correctly recognized that segregation takes place "only at the stage at which the reproductive cells develop" (i.e., during meiosis). This paragraph, however, reveals one aspect of Mendel's perception that differs from the modern concept of segregation. o Mendel perceived segregation as an anomaly restricted to hybrids (heterozygotes). o He called the differing elements "antagonistic elements" whose association in the hybrid is a "compromise," and wrote that "only those elements that differ separate from one another." Mendel represented heterozygotes with a two-letter designation (Aa), as modern geneticists usually represent them, he consistently represented homozygotes with a single letter (A or a), rather than the two letters (AA or aa) used today