Problems 50 through 57
Mendelian NonMendelian problem package 2018 Tom Mueller RHS Mendel & Nonmendelian Problems Name: Dominant: tall stems, coloured seed coats, green pods, yellow seeds, purple flowers, round seeds, axial flowers Recessive: short stems, white seed coats, yellow pods, green seeds, white flowers, wrinkled seeds, terminal flowers height coats pods seed color shape flower Dominant: Recessive: 1. Using the symbols from the above chart, write the allele symbols that would be present in the following homozygotes. Next, indicate whether they are going to express the dominant or recessive trait. tall stemmed plants ______________ __________________________________________ terminal flowers ______________ __________________________________________ white seed coats ______________ __________________________________________ yellow seeds ______________ __________________________________________ yellow pods ______________ __________________________________________ 2. Write the symbols for the following heterozygotes yellow seeded peas ______________ round seeds ______________ colored seed coats ______________ axial flowers ______________ green podded peas ______________ tall stemmed plants ______________ 3. The following letters represent pairs of alleles. Indicate whether each pair is a heterozygote or homozygote. Then indicate whether each pair would display a dominant or recessive phenotype. Cc _____________________________ TT ___________________________________ yy _____________________________ Gg ____________________________________ 4. What percent of the alleles does each parent contribute to their offspring? _______________ 5. What are the phenotypes for the following dihybrids: TtCc ___________________________ AaRr ___________________________ GgYy ___________________________ TtAa ___________________________ Single Trait Crosses (Monohybrid) 6. Tall pea plants are dominant over short pea plants. Pollen from a homozygous tall parent is applied to another homozygous tall parent. Like any language, the language of genetics consists of symbols and rules for using these symbols. The capitalized letter of the dominant form becomes its symbol (Ex. R stands for round seeds). For the recessive form of the same trait (the recessive allele); the symbol remains the same but not capitalized (Ex. r stands for wrinkled seeds). Two versions (i.e. alleles) of one gene require two versions of one symbol. Note: frequency has nothing to do with dominance. Sometimes the dominant form is more frequent (brunettes in Korea) and sometimes the recessive form is more frequent (blondes in Finland). Complete the following chart using these rules of symbols. Memory trick for our class: Male Gametes = Sperm swim to the top Female Gametes = Eggs on the side (sunny side up) It really doesn’t matter, but let’s do it the same way in class. For now, write the alleles on the gametes shown. Tom Mueller RHS 7. If two heterozygous yellow seeded plants are crossed: 8. If two white flowered plants are crossed, then 9. If pollen from a hybrid Green Podded 10 If pollen from a purebred Axial-flowered plant is crossed is crossed with a Yellow-podded Plant, with a Terminal-flowered plant In a certain species of rat, black color dominates over white. 11. Cross two hybrid black rats 12. Cross a heterozygous male black rat with a white rat 13. If black fur is dominant to white fur in rabbits, what would be the genotypic and phenotypic ratios resulting from the following crosses? a. homozygous black males b. two heterozygotes? and white females? c. a homozygous black male d. a heterozygous black male and a white female? and a white female? 14 The last two examples (c & d) are called “test crosses”! Explain what that means in your own words: _____________________________________________________________________________________________ Tom Mueller RHS Exceptions to Mendel’s Laws: Incomplete Dominance Mendel had good fortune to study pea plants and not Snapdragons. With Mendelian dominance, alleles can sometimes be dominant when only one copy of an enzyme is present in the cytoplasm. Consider the possible scenario where the presence of Dad’s enzyme masks the absence of Mom’s enzyme: that means Dad’s allele is dominant. Sometimes, gene dosage is important. In the case of Snapdragons, the red phenotype only occurs when both Dad’s and Mom’s alleles both are simultaneously expressed. When only one functional allele is expressed, a pink phenotype results. Two non- functional alleles become white. Incomplete dominance looks like “blending”. When describing symbols, you must define all possible genotypes: For example, with Japanese four o'clock plants, you must write: RR = red; Rr = pink; rr = white In Japanese four o'clock plants, the flowers may be red or white in the purebred form. But, in the hybrid form the flowers are pink and therefore show incomplete dominance. This is an example of “____________________________ dominance” 15. What would be the possible genotypes and 16. What would be the possible genotypes and phenotypes resulting from a cross between phenotypes resulting from a cross between pollen from a pink parent crossed pollen from a pink parent crossed with a red parent?