Final answer:
Mendel's idea that 'elementen' separate during gamete formation is called the law of segregation. This law explains that alleles segregate from each other during gamete formation, and it formed the basis for Mendel's observations of phenotypic ratios in his pea plant experiments. Option number 2 is correct.
Step-by-step explanation:
Mendel's idea that “elementen” separate during gamete formation is known as the law of segregation. This fundamental principle of genetics states that each individual possesses pairs of alleles (versions of a gene) for a particular trait, and that these alleles segregate from each other during the production of gametes. In essence, during gamete formation such as in the process of meiosis, each gamete receives only one allele from each allele pair.
Additionally, the law of segregation is observable in the characteristic phenotypic ratios Mendel discovered in his pea plant experiments. For example, when observing a monohybrid cross, Mendel noticed that the F2 generation showed both dominant and recessive traits in a predictable 3:1 ratio, which further supported the equal segregation of alleles. This equal segregation is what allows for the use of tools such as the Punnett square to forecast the genetic outcomes of specific matings.
Furthermore, it's essential to understand that Mendel's recognition of the segregation of alleles was critical to the development of the field of genetics. Although the specifics of meiotic cell division were not known at his time, today we recognize that the disjunction of homologous chromosomes during meiosis I is the cellular basis for the law of segregation.