7/31/2019 Outline 11-1 Origins of Genetics 7/31/2019

I. Mendel Studied Peas A. Heredity 1. Passing of traits from parents to offspring B. Genetics 1. The study of heredity C. Gregor Mendel 1. Austrian monk who studied the heredity of traits in garden peas 2. First person to count the kinds of offspring & analyze the data 7/31/2019

D. Useful Features of Peas 1. Many traits with just two forms a. Purple vs white flowers b. Yellow vs green seeds (See Figure 11-3, p. 264) 2. Plant is easily grown & makes many offspring 3. Mating can be easily controlled by human interference 7/31/2019

1. Self-fertilization (pollination) E. Flower Reproduction 1. Self-fertilization (pollination) a. Flower fertilizes itself because it has both male & female parts  Male part = stamen Produces pollen & then sperm  Female part = pistil Produces ovary & eggs 7/31/2019

(stamens) (pistil)

a. Pollen from one plant fertilizes the flower of a different plant 2. Cross-Pollination a. Pollen from one plant fertilizes the flower of a different plant  Mendel removed the stamens & dusted pollen on pistils 7/31/2019

F. Mendel’s Experiments & Results 1. Allowed plants to self-pollinate for several generations a. This created true- breeding varieties b. These would serve as the parental, or P1 generation 2. Crossed 2 plants that had one type of contrasting trait a. Tall plant X short plant b. This type of cross is called a monohybrid cross 7/31/2019

 They were all tall; no short c. The offspring of this cross were called the first filial generation, or the F1 generation 3. At the end of each generation he counted how many of each type of plant was produced a. The F1 generation plants always showed only one form of the trait. One form seemed to disappear.  They were all tall; no short 7/31/2019

Mendel’s F1 Results

In ALL cases one trait seemed to disappear in the F1 offspring

4. Allowed F1 plants to self-pollinate a. These offspring were called the second filial, or F2 generation b. When Mendel counted he got the following results:  The missing trait reappeared!  787 plants were tall while 277 short c. The ratio of the two numbers was 787:277. When reduced you get 2.84 : 1, approximately 3 : 1 d. Mendel got this ratio for ALL traits 7/31/2019

Mendel’s Results F1 Generation F2 Generation Tall Tall Tall Tall Tall 7/31/2019 Mendel’s Results F1 Generation F2 Generation When Mendel allowed the F1 plants to reproduce by self-pollination, the traits controlled by recessive alleles reappeared in about one fourth of the F2 plants in each cross. Tall Tall Tall Tall Tall Short Tall Short