11.1 Gregor Mendel
A. The Blending Concept of Inheritance 1. This theory stated that offspring would have traits intermediate between those of the parents. 2. Red and white flowers produce _____pink____________ flowers; any return to red or white offspring was considered instability in the genetic material. 3. Charles Darwin wanted to develop a theory of evolution based on hereditary principles; blending theory was of no help. a. A blending theory did not account for variation (differences) and could not explain species diversity.
B. Mendel’s Particulate Theory of Inheritance 1. Mendel was an Austrian monk. 2. Mendel formulated two fundamental laws of heredity in the early 1860s. 3. He had previously studied science and mathematics at the University of Vienna. 4. At time of his research, he was a substitute science teacher at a local technical high school. 5. Because Mendel had a mathematical background, he used a statistical basis for his breeding experiments. 6. Mendel’s particulate theory is based on the existence of minute particles—now called genes.
C. Mendel Worked with the Garden Pea 1. Mendel prepared his experiments carefully and conducted preliminary studies. a. He chose the garden pea, Pisum sativum, because peas were easy to cultivate, had a short generation time, and could be cross-pollinated by hand. b. From many varieties, Mendel chose 22 true-breeding varieties for his experiments. c. True-breeding varieties had all offspring like the parents and like each other. d. Mendel studied simple traits (e.g., seed shape and color, flower color, etc.). 2. He used his understanding of mathematical principles of probability to interpret results.
11.2 Mendel’s Law
A. Law of Segregation 1. Mendel confirmed that his tall plants always had tall offspring, i.e., were true-breeding, before crossing two different strains that differed in only one trait—this is called a _________monohybrid________cross. 2. A _________monohybrid________cross is between two parent organisms true-breeding for two distinct forms of one trait. 3. Mendel tracked each trait through two generations. a. __P__generation is the parental generation in a breeding experiment. b. ___F1_ generation is the first-generation offspring in a breeding experiment. c. __F2__ generation is the second-generation offspring in a breeding experiment. 4. He performed _____reciprocal____________crosses, i.e. pollen of tall plant to stigma of short plant and vice versa. 5. His results were contrary to those predicted by a blending theory of inheritance. 6. He found that the F1 plants resembled only one of the parents. 7. Characteristics of other parent reappeared in about ¼ of F2 plants; ¾ of offspring resembled the F1 plants. 8. Mendel saw that these 3:1 results were possible if: a. F1 hybrids contained two factors for each trait, one being ____dominant_____________and the other ______recessive___________; b. factors separated when gametes were formed; a gamete carried one copy of each factor; c. and random fusion of all possible gametes occurred upon fertilization. 9. Results of his experiments led Mendel to develop his first law of inheritance—the law of _______segregation__________: a. Each organism contains two factors for each trait. b. Factors segregate in the formation of gametes. c. Each gamete contains one factor for each trait. d. Fertilization gives each new individual two factors for each trait. B. Mendel’s Cross as Viewed by Classical Genetics 1. The _________gene locus_________________________is the specific location of alleles on homologous chromosomes. 2. Alternate versions of a gene are called