GENES AND TRAITS • ACTIVITY 5 SAMPLE RESPONSES 1. Genotype refers to the set of alleles that an organism inherits. Phenotype refers to the traits exhibited by the organism based on the alleles (genotype) it has inherited. For example, a corn kernel that is heterozygous for corn color has a genotype of Pp and a phenotype of purple kernels. 2. Simple dominance occurs when, of two possible traits, one is recessive and one is dominant. A heterozygous individual will have the phenotype of the dominant trait. Incomplete dominance is different in that neither trait is dominant. If an organism is heterozygous, the trait will be a blend of or intermediate between the two. In codominance a heterozygous organism will express the phenotype of both traits. 3. In most cases, both phenotype and genotype are altered. A new gene is inserted, which changes the corn’s genotype, and the insertion of the gene causes a change in a trait, which is an organism’s phenotype. Thus, both the Bt corn’s phenotype and genotype were altered. GENES AND TRAITS • ACTIVITY 5 11 3. Think back to the Bt corn you considered in Activity 1, “A Genetically Modified Solution?” When an organism is genetically modified, which of the following is changed: genotype, phenotype, both, or neither? Explain. 4. The following is a list of a few traits in plants and animals. Determine if the traits described are examples of simple dominance, codominance, or incomplete dominance. Explain your reasoning. Trait Description Feather color in chickens The feathers of a species of chicken can be black, white, or “erminette.” Erminette chickens have both black feathers and white feathers, but not gray feathers. Sweet pea tendrils When sweet pea plants with tendrils (structures that grow from the stem and help the plant attach and climb) are crossed with sweet pea plants without tendrils, all of the resulting sweet peas have tendrils. Rabbit hair length Longhaired rabbits crossed with shorthaired rabbits produce offspring that have medium-length hair. KEY VOCABULARY allele homozygous codominance incomplete dominance dominant phenotype gamete Punnett square gene recessive genotype selective breeding heredity trait heterozygous Sample Student Response to Analysis Question 4 Trait Description Type of dominance and reasoning Feather color in chickens The feathers of a species of chicken can be black, white, or erminette. Erminette chickens have both black feathers and white feathers, but not gray feathers. Codominance because both traits are expressed (feathers are white and black), and they do not blend as they would with incomplete dominance (no gray feathers) Sweet pea tendrils When sweet pea plants with tendrils (structures that grow from the stem and help the plant attach and climb) are crossed with sweet pea plants without tendrils, all of the resulting sweet peas have tendrils. 299 Simple dominance because the dominant trait (tendrils) masks the recessive trait (no tendrils) Rabbit hair length Longhaired rabbits crossed with shorthaired rabbits produce offspring that have mediumlength hair. Incomplete dominance because the offspring have medium-length hair which is a blend of the two traits (long and short) 4. Samples of students’ answers are shown at right in the third column. REVISIT THE CHALLENGE Type of dominance and reasoning Students should be able to articulate that observing the traits of offspring over multiple generations provides information about the genetic makeup of parents and shows how those specific traits are inherited. Students modeled this process in Activity 4, “Breeding Corn,” when they counted the corn kernels by color and with that determined the genotype of the parent corn. Mendel used this same process to propose the fundamental rules of heredity, which explain how traits are passed from one generation to the next. Students should also be able to explain that not all traits are simply dominant and recessive, and that other patterns, such as codominance and incomplete dominance, are exhibited with many traits. Emphasize that most traits are influenced by multiple genes and by environmental factors. 463