Problems #1-8 involve Mendelian genetics. Mendelian traits are controlled by a single gene with exactly two (2) alleles. One allele is dominant and the other allele is recessive. Dominant alleles are represented by capital letters while recessive alleles are represented by the corresponding lower-case letter. Actual letter choices are a matter of personal preference but the convention is to use the first letter of the dominant trait. Question #1: In the pea plants that Mendel worked with, tall stems are dominant over short stems. This trait displays complete dominance. Tall stem allele = T Short stem allele = t If you cross a homozygous dominant tall plant with a short plant, what will the predicted phenotypic and genotypic ratios be for the F1 offspring be? First write out the genotypes of the parent plants and then complete the Punnett square. Then answer the question. Question #2: Suppose two of the F1 offspring are allowed to self-pollinate. What will the predicted phenotypes and genotypes of the F2 generation be? Complete the Punnett square on the next page.
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We are crossing a homozygous dominant tall plant with a short plant. The genotypes of the parent plants are: Tall plant: TT (homozygous dominant) Short plant: tt (homozygous recessive) Now, let's complete the Punnett square: | | T | T | |---|---|---| | t | Show more…
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Assume tall (T) is completely dominant to dwarf (t) in a certain species of plant. If a homozygous dominant individual is crossed with a homozygous dwarf individual, what are the genotype and phenotype ratios of the offspring plants? In pea plants, tall is dominant to short. If a tall plant is mated with a short plant, what are the possible genotypes for the parent plants? (Think carefully; how do we determine the genotype of the tall plant? You cross the tall and short parent plants and have 78 offspring plants; 35 are tall and 38 are short. What is the genotype of the tall plant? Pea flowers may be purple or white (P). Pea seeds may be round (R) or wrinkled (r). You do a dihybrid cross for these traits. Out of 1000 offspring, how many would you expect to have the following: - All white flowers and wrinkled seeds - Purple flowers and wrinkled seeds - White flowers and round seeds - Purple flowers and round seeds How many would you expect to be homozygous dominant for both traits? (Advanced question) If a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous?
Shaiju T.
Table 1: Mendel's Traits and Symbols for Pea Plants Traits Dominant Allele Symbol Recessive Allele Symbol Seed Shape Round R Wrinkled r Seed Color Yellow Y Green y Pod Shape Smooth S Constricted s Pod Color Green G Yellow g Plant Height Tall T Short t Flower Position Axial A Terminal a Refer back to Table 1 on the first page of this assignment to answer the following two questions. Use the appropriate symbols and phenotypes in your answer. 1. Show the genotypes of the parents in the following crosses (2): a) A plant with green, wrinkled seeds is crossed with a plant that is known to be heterozygous for both seed color and seed shape: b) A plant that is heterozygous tall with terminal flowers is crossed with a plant that is short with homozygous axial flowers: 2. For the following two-trait cross: - Make a Punnett square to determine the possible genotype outcomes for this cross. - State the phenotype and genotype ratios of the offspring. (2 points) Parental genotypes: Ggss x ggSs
Suman K.
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