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Seed color is governed by a single gene with two alleles. We will use a second trait that Mendel investigated, seed color, as an example. For example, the phenotypes that Mendel observed in his crosses between pea plants with differing traits are connected to the diploid genotypes of the plants in the P, F 1, and F 2 generations. Mendel’s hybridization experiments demonstrate the difference between phenotype and genotype. An organism’s underlying genetic makeup, consisting of both the physically visible and the non-expressed alleles, is called its genotype. The observable traits expressed by an organism are referred to as its phenotype. Two alleles for a given gene in a diploid organism are expressed and interact to produce physical characteristics. Mendel examined the inheritance of genes with just two allele forms, but it is common to encounter more than two alleles for any given gene in a natural population. Gene variants that arise by mutation and exist at the same relative locations on homologous chromosomes are called alleles. For example, one individual may carry a gene that determines white flower color and a gene that determines violet flower color. The offspring are formed when that gamete unites with one from another parent and the two copies of each gene (and chromosome) are restored.įor cases in which a single gene controls a single characteristic, a diploid organism has two genetic copies that may or may not encode the same version of that characteristic. This separation, or segregation, of the homologous chromosomes means also that only one of the copies of the gene gets moved into a gamete. Recall that in meiosis these chromosomes are separated out into haploid gametes. In fact, it is the chromosomes we inherit and the two copies of each gene are located on paired chromosomes. The reason we have two copies of each gene is that we inherit one from each parent. We now call those two copies genes, which are carried on chromosomes. Mendel deduced from his results that each individual had two discrete copies of the characteristic that are passed individually to offspring. The seven characteristics that Mendel evaluated in his pea plants were each expressed as one of two versions, or traits.