Final answer:
Mendel's idea of segregation is best described by offspring inheriting a mixture of their parents' traits, where alleles for each trait separate during gamete formation, giving rise to the discrete transmission of inherited characteristics.
Step-by-step explanation:
The principle of Mendel's idea of segregation can be best described by option d) Offspring inherit a mixture of their parents' traits. This is outlined in Mendel's law of segregation which states that alleles, the different versions of a gene, separate during the creation of gametes (eggs and sperm). Each parent contributes one unit, or allele, for each trait to their offspring. During fertilization, alleles from both parents combine randomly to form the child's genotype.
Mendel's groundbreaking work with pea plants led him to realize that traits do not blend in the offspring, but rather, each trait is inherently separate and transmitted discretely through what we now understand are alleles on chromosomes. This was an essential departure from the blending theory of inheritance prevailing at the time, which suggested that offspring would have a mix of parental traits.
The law of segregation ensures that each gamete carries only one allele for any given trait, and the combination of gametes during fertilization restores the two-gene state. Moreover, Mendel's laws laid the foundation for the development of modern genetics, moving away from the previously held belief that offspring were a simple blend of parental characteristics.