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In the P generation, half of the plants are phenotypically tall and half are dwarf. In contrast, the F1 generation is heterozygous, with the genotype Tt, because every individual carries one copy of the tall allele and one copy of the dwarf allele. A heterozygous individual carries different alleles of a gene. ) Although these plants are heterozygous, their phenotypes are tall because they have a copy of the dominant tall allele. 6). Because the parents of the F2 generation are heterozygous, each parent can transmit either a T allele or a t allele to a particular offspring, but not both, because each gamete carries only one of the two alleles.

His work provided the conceptual framework for transmission genetics. In particular, he originated the idea that genetic determinants, which we now call genes, are passed as discrete units from parents to offspring via sperm and egg cells. Since these pioneering studies of the 1860s, our knowledge of genetic transmission has greatly increased. Many patterns of genetic transmission are more complex than the simple Mendelian patterns that are described in Chapter 2. The additional complexities of transmission genetics are examined in Chapters 3 through 8.

As described next, this quantitative approach allowed him to make a third proposal—genes segregate from each other during the process that gives rise to gametes. A self-help quiz involving this experiment can be found at the Online Learning Center. P generation in this experiment. The term phenotype refers to an observable characteristic of an organism. In the P generation, half of the plants are phenotypically tall and half are dwarf. In contrast, the F1 generation is heterozygous, with the genotype Tt, because every individual carries one copy of the tall allele and one copy of the dwarf allele.