Fast Plants Genetics Lab Learning Standards: C2. Explain how each chromosome pair contains two alleles of each of many distinct genes, and that one allele is passed down from each parent to offspring. B1. Describe how dominant and recessive traits are inherited. A1. Use historical and your own data and observations as evidence on which to base scientific explanations and predictions. Background Gregor Mendel’s research on pea plants paved the way for our modern understanding of inheritance. The data he collected help explain heredity (what traits are passed from one generation to the next) and variation (the differences between parents and their offspring). Mendel observed patterns in the number of phenotypes occurring in the different generations of his garden peas. Phenotype is a discernible expression of an offspring’s genetic traits. Examples of phenotypes in peas include yellow or white flowers, or tall or short plants. Mendel’s experiments also helped him determine that each gene could have more than one version (just like ice cream can have more than one flavor). For example, in the gene for flower color, peas expressed a pink version or a white version. All the versions of a gene are called alleles. Some alleles display dominance and some display a recessive tendency. Mendel noticed that when a dominant allele was combined with a recessive allele, only the dominant allele was expressed in the phenotype. In modern genetics, a dominant allele is notated with a capital letter (for example, T for tall), and a recessive allele is notated with a lowercase letter (t for short). The combination of alleles an organism carries (Tt) is its genotype. Genotype (Tt) determines phenotype (tall). Based on his data and observations, Mendel developed two important scientific explanations: 1. The Law of Segregation: Organisms have 2 alleles for each trait. When 2 organisms are crossed, their offspring receive 1 allele for each trait from each parent. 2. The Law of Independent Assortment: All the traits an offspring has are inherited independently of each other. For example, just because you inherit blonde hair doesn’t mean you’ll also inherit blue eyes – traits for hair color don’t determine traits for eye color, and vice versa. The fast plants in this lab carry the gene for 2 possible stem colors: purple or non-­‐purple (green). Plants that display the purple stem phenotype produce a pigment called anthocyanin. Plants that display a green phenotype do not produce this pigment. (Fun fact: anthocyanin is the same pigment that gives berries their pinky-­‐purple color, and may be responsible for the antioxidant properties associated with those “super foods.”) In this lab, you will observe a group of plants from the parent generation (we’ll call them P1 and P2). Then, you’ll plant and grow a group of their offspring, called first-­‐generation plants (F1). After observing and recording data on the F1 generation, you will harvest their seeds and plant them. These seeds will produce the F2 generation. While growing the plants, you’ll be making observations and collecting data about the phenotype and genotype of each plant. Just like Mendel, you’ll use these data and observations to support scientific explanations on the patterns of inheritance for traits in your plants.