Gregor Mendel Discovered the Basic Principles of Heredity

Gregor Mendel Discovered the Basic Principles of Heredity Genetic

Mendel’s Success § Mendel’s approach to the study of heredity was effective for several reasons. § Foremost was his choice of experimental subject, the pea plant Pisum sativum, which offered clear advantages for genetic investigation. § The plant is easy to cultivate, and Mendel had the monastery garden and greenhouse at his disposal.

§ The significance of Mendel’s discovery was not recognized until 1900, when three botanists, independently conducting similar experiments with plants and arrived at conclusions similar to those of Mendel. § Compared with some other plants, peas grow relatively rapidly, completing an entire generation in a single growing season. § By today’s standards, one generation per year seems frightfully slow—fruit flies complete a generation in 2 weeks and bacteria in 20 minutes.

Ø But Mendel was under no pressure to publish quickly and was able to follow the inheritance of individual characteristics for several generations Ø Pea plants also produce many offspring—their seeds —which allowed Mendel to detect meaningful mathematical ratios in the traits that he observed in the progeny.

§ The large number of varieties of peas that were available to Mendel also was crucial, because these varieties differed in various traits and were genetically pure. § Mendel was therefore able to begin with plants of variable, known genetic makeup.

Much of Mendel’s success can be attributed to the seven characteristics that he chose for study.

Genetic Terminology § The genotype is the set of alleles that an individual organism possesses. § A diploid organism with a genotype consisting of two identical alleles is homozygous for that locus. § One that has a genotype consisting of two different alleles is heterozygous for the locus. § Another important term is phenotype, which is the manifestation or appearance of a characteristic.

Genetic Terminology

Monohybrid Crosses Reveal the Principle of Segregation and the Concept of Dominance

§ Mendel started with 34 varieties of peas and spent 2 years selecting those varieties that he would use in his experiments. § He verified that each variety was pure-breeding (homozygous for each of the traits that he chose to study) by growing the plants for two generations and confirming that all offspring were the same as their parents. § He then carried out a number of crosses between the different varieties.

§ Although peas are normally self-fertilizing (each plant crosses with itself). § Mendel conducted crosses between different plants by opening the buds before the anthers (male sex organs) were fully developed, removing the anthers, and then dusting the stigma (female sex organs) with pollen from a different plant’s anthers

§ Mendel began by studying monohybrid crosses— those between parents that differed in a single characteristic. § In one experiment, Mendel crossed a pure-breeding (homozygous) pea plant for round seeds with one that was pure-breeding for wrinkled seeds. § This first generation of a cross is the P (parental) generation.

§ The offspring from the parents in the P generation are the F 1 (filial 1) generation. § When Mendel examined the F 1 generation of this cross, he found that they expressed only one of the phenotypes present in the parental generation: all the F 1 seeds were round.

References § Benjamin A. Pierce, 2010. Genetics: A Conceptual Approach, 4 th Edition. W. H. Freeman.

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