In plants, pollen carries the male gametes (sperm) to the stigma, a sticky organ that traps pollen and allows the sperm to move down the pistil to the female gametes (ova) below. In the pea, this is done by manually transferring pollen from one pea plant to the stigma of another pea plant. Mendel performed hybridizations, which involve mating two true-breeding individuals that have different traits. Finally, large quantities of garden peas could be cultivated simultaneously, allowing Mendel to conclude that his results did not come about simply by chance. The garden pea also grows to maturity within one season, meaning that several generations could be evaluated over a relatively short time. By experimenting with true-breeding pea plants, Mendel avoided the appearance of unexpected traits in offspring that might occur if the plants were not true breeding. These are plants that always produce offspring that look like the parent. The result is highly inbred, or “true-breeding,” pea plants. The flower petals remain sealed tightly until after pollination, preventing pollination from other plants. This species naturally self-fertilizes, such that pollen encounters ova within individual flowers. Mendel’s seminal work was accomplished using the garden pea, Pisum sativum, to study inheritance. In fact, it was not until 1900 that his work was rediscovered, reproduced, and revitalized by scientists on the brink of discovering the chromosomal basis of heredity. He was not recognized for his extraordinary scientific contributions during his lifetime. In 1868, Mendel became abbot of the monastery and exchanged his scientific pursuits for his pastoral duties. Mendel’s choice of these kinds of traits allowed him to see that the traits were not blended in the offspring, nor were they absorbed, but rather that they kept their distinctness and could be passed on. These traits display discontinuous variation. Mendel worked with traits that were inherited in distinct classes, such as violet versus white flowers. Offspring appear to be a “blend” of their parents’ traits when we look at characteristics that exhibit continuous variation.

Continuous variation results when many genes work together to determine a characteristic, such as human height or eye color. Mendel’s work went virtually unnoticed by the scientific community that believed, incorrectly, that the process of inheritance involved a blending of parental traits that produced an intermediate physical appearance in offspring this hypothetical process appeared to be correct because of what we know now as continuous variation. In 1866, he published his work, Exp eriments in Plant Hybridization in the proceedings of the Natural History Society of Brünn. He demonstrated that traits are transmitted faithfully from parents to offspring independently of other traits and in dominant and recessive patterns. In 1865, Mendel presented the results of his experiments with nearly 30,000 pea plants to the local Natural History Society. In 1856, he began a decade-long research pursuit involving inheritance patterns in honeybees and plants, ultimately settling on pea plants as his primary model system. Supported by the monastery, he taught physics, botany, and natural science courses at the secondary and university levels. Thomas in Brno in what is now the Czech Republic. As a young adult, he joined the Augustinian Abbey of St. Johann Gregor Mendel (1822–1884) was a lifelong learner, teacher, scientist, and man of faith.

Describe the expected outcomes of monohybrid crosses involving dominant and recessive alleles.

Describe the scientific reasons for the success of Mendel’s experimental work.

18.1 | Mendel’s Experimentsīy the end of this section, you will be able to: Not all genes are transmitted from parents to offspring according to Mendelian genetics, but Mendel’s experiments serve as an excellent starting point for thinking about inheritance. Today, the postulates put forth by Mendel form the basis of classical, or Mendelian, genetics. We now know that genes, carried on chromosomes, are the basic functional units of heredity with the capability to be replicated, expressed, or mutated. Because of Mendel’s work, the fundamental principles of heredity were revealed. Mendel selected a simple biological system and conducted methodical, quantitative analyses using large sample sizes. Johann Gregor Mendel (1822–1884) set the framework for genetics long before chromosomes or genes had been identified, at a time when meiosis was not well understood ( Figure 18.2). Introduction Figure 18.2 Johann Gregor Mendel is considered to be the father of genetics.

18.3 Exceptions to Mendel’s Principles of Inheritance.

18.2 Mendel’s Principles of Inheritance.

Mendel principle of dominance quizlet