Chapter 5 Section 1 Outline Completed

Mendel’s Work I. Mendel’s Experiments A. Vocabulary Words for entire section 1. Heredity- The passing of traits from parents to offspring for example, a pea plant having the same stem height as its parent plant. 2. Trait- A characteristic that an organism can pass on to its offspring through its genes for example, stem height. 3. Genetics- The scientific study of heredity. 4. Fertilization- The joining of a sperm and an egg. 5. Purebred- The off spring of many generations that have the same traits for example, stem height or flower color. 6. Gene- The set of information that controls a trait; a segment of DNA on a chromosome that codes for a specific trait. 7. Alleles- The different forms of a gene. 8. Dominant and recessive allele- A dominant allele’s traits will always show up in an organism if it is present overriding present recessive alleles. A recessive allele’s traits will be masked if the dominant allele is present. 9.Hybrid- An organism that has two different alleles for a trait; an organism that is heterozygous for a particular trait. B. How did Mendel perform his research- Mendel experimented with thousands of pea plants examining the plants’ traits. 1.What type of traits did Mendel study- Seed color, stem height, flower position, seed shape, pod shape, and pod color 2. What results did Mendel get from his study- Mendel found out that certain traits were passed only if both parents had the trait, while other traits seemed hidden. a. F1 Offspring-Mendel mixed purebred pea plants and the first mix from this cross was called the F1 generation which showed the dominant trait. For example, a tall and short plant produced only tall plants. b. F2 Offspring- The mix of two F1 offspring produced plants that showed both traits. The tall plants from the above mix produced both tall and short plants. 3. Key Idea- In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants. II. Dominant and Recessive Alleles A. Key Idea- An organism’s traits are determined by the alleles it inherits from its parents. Some alleles are dominant while other alleles are recessive.

1. When do recessive alleles show up?- It is hidden when a dominant allele

is present, only when there is not a dominant allele does the recessive allele show itself. 2. Which was dominant and which was recessive for plant stems? The tall stems were dominant while the short stems were recessive. a. What were the plant’s stems like for each generation of the pea plants? In the first generation all the plants were tall while in later generations about one fourth of the plants had short stems. 3. Symbols for alleles- A dominant allele is represents by a capital letter, while the recessive allele is shown with a lower case letter. B. Significance of Mendel’s Contributions- Changed how scientists viewed heredity. 1. How genetics work- People originally believed the a mix of traits would produce a trait that was partial while in reality one trait would override another trait. 2. When was the importance of Mendel’s discovery recognized- Mendel’s importance was recognized in 1900 by three different scientists.

Padilla, Michael J., et al. Focus on California Life Science. Boston, MA: Pearson Prentice Hall, 2008.