Final answer:
Mendelian inheritance is the inheritance of traits controlled by single genes with two alleles, with individuals being diploid and possessing two genetic copies of each gene. Mendel's pea plant experiments led to the understanding that traits are passed from parents to offspring, with each contributing one allele per gene. More genetic variation exists in natural populations with multiple alleles present than in Mendel's experiments.
Step-by-step explanation:
Mendelian inheritance refers to the patterns of inheritance for traits that are controlled by single genes with two alleles, one of which may be dominant over the other. Individuals, being diploid, carry two genetic copies of each gene, which are located on homologous chromosomes. These two copies, called alleles, may be identical or may differ if mutations have occurred.
Gregor Mendel, through his experiments with pea plants, found that traits are inherited independently from each parent, with each parent contributing one allele per gene. In the case of traits controlled by two alleles, individuals may be homozygous with two identical alleles like AA, BB, or OO, or heterozygous with two different alleles, such as AB.
While Mendel worked with genes that had only two allele forms, in natural populations, multi-allele genes are common. For example, three possible gene sequences determine the human blood type, and each person inherits a combination of these genes from their parents. Therefore, genetic variation within a species is due to the specific combination of genes inherited from both parents.