The Origins of Genetics Section 8-1

Mendel and Others Studied Garden- Pea Traits Many of your traits resemble those of your parents. The passing of traits from parents to offspring is called HEREDITY.

Mendel and Math Scientific study of heredity began more than a century ago with the work of an Austrian monk named Gregor Mendel. Bred different varieties of the garden pea British farmers had performed similar breeding experiments more than 200 years earlier, but Mendel was the first to develop rules that accurately predicted patterns of heredity.

Mendel and Math (con’t) The patterns that Mendel discovered form the basis of genetics, the branch of biology that focuses on heredity. Mendel repeated experiments of T.A. Knight. Knight had crossed a variety of garden pea that had purple flowers with a variety that had white flowers. Cross refers to the mating/breeding of two individuals.

Mendel and Math (con’t) All of the offspring of Knight’s crosses had purple flowers. However, when two of the purple-flowered offspring were crossed, their offspring showed both white and purple flowers. The white trait had reappeared in the second generation.

Mendel and Math (con’t) Mendel’s experiments differed from Knight’s because Mendel counted the number of each kind of offspring and analyzed the data. Quantitative approaches to science – those including measuring and counting – were on the cutting edge of research at the time.

Useful Features in Peas 1.The garden pea has many traits that have two clearly different forms that are easy to tell apart. 2.The mating of the garden-pea flowers can easily be controlled because the male and female reproductive parts are enclosed within the same flower. Can allow self- fertilization (fertilize itself) or can cross- pollinate (transfer pollen to another flower on different plant).

Useful Features in Peas (con’t) 3.The garden pea is small, grows easily, matures quickly, and produces many offspring. Allows results to be obtained quickly, and there are plenty of subjects to count.

Mendel Observed that Traits are Expressed as Simple Ratios Mendel’s initial experiments were monohybrid crosses. Monohybrid Cross – cross involving one pair of contrasting traits. EXAMPLE: cross between a purple flowered plant and a white flowered plant

Three Steps of Mendel’s Experiments 1.Mendel allowed each variety of garden pea to self-pollinate for several generations. This ensured that each variety was true-breeding for a particular trait (all offspring would display only one form of a particular trait). The true- breeding plants served as the parental generation or P generation (first two individuals crossed in breeding experiment).

Three Steps of Mendel’s Experiments 2. Mendel then cross-pollinated two P generation plants that had contrasting forms of a trait. Mendel called the offspring of the P generation the first filial generation or the F1 generation. He then examined each F1 plant and recorded the number of F1 plants expressing each trait.

Three Steps of Mendel’s Experiments 3. Finally, Mendel allowed the F1 generation to self-pollinate. He called the offspring the second filial generation or the F2 generation. Again, each F2 plant was counted and characterized.

Mendel’s Results Each of the F1 plants showed only one form of the trait. When F1 generation self-pollinated, the second trait reappeared in some plants in F2 generation. When purple flowers were crossed with white flowers, all of the F1 generation was purple flowers.

Mendel’s Results (con’t) When he crossed two of the F1 offspring, the F2 generation would have purple flowers and white flowers in a 3:1 ratio. This was true for each of the seven traits Mendel studied.

Summary Gregor Mendel bred varieties of the garden pea in an attempt to understand heredity. Mendel observed that contrasting traits appear in offspring according to simple ratios. F1 generation only expressed one trait. In F2 generation, the second trait reappeared in a 3:1 ratio.

Homework Section 8-1 Review Questions p. 163 #1-5 Math Lab p. 163 #1-3