Genetics problems

1. In pea plants, round pea shape (R) is dominant to wrinkled pea shape (r) and green pod color (G) is dominant to yellow pod color (g). True-breeding wrinkled, green pod plants are bred to true-breeding round, yellow pod plants, yielding F1. The F1 plants are interbred to yield F2. 2. In garden tomatoes, round fruit (R) is dominant to oval fruit (r). Yellow fruit color (CY) is co-dominant with red fruit color (CR), such that the heterozygote CYCR has fruit with red and yellow splotches. What are the expected phenotypic results for the self-cross of double-heterozygous plant? Begin by determining the correct phenotype and genotype for the parent plant. 3. Garden tomatoes also have the incompletely dominant alleles H (tall) and h (short), where heterozygous Hh plants are of medium height. Determine the expected phenotypic results for the self-cross of RrCYCRHh plants. 4. In cats, the genotypes AA and Aa produce tabby (stripe) markings, while aa produces solid black fur. Epistatic to the A/a gene is W/w, where presence of a single W allele (so, WW or Ww) blocks production of any pigment, resulting in a white cat. Determine the expected phenotypic results for the cross of AaWw and AaWw cats. 5. A rare breed of elephants has tusk number and ear size determined by incomplete dominance. TT elephants have two tusks and tt elephants have none. EE elephants have large ears while ee elephants have very small ears. 6. Horses have three possible base coat colors: chestnut (Ch), black (Bk), and bay (By), determined by epistasis of two alleles: E/e and S/s. Allele E is dominant to e and encodes an enzyme that produces dark pigment. S is dominant to s and causes the dark pigment to be evenly distributed. Ch horses have genotype ee, so produce no dark pigment and are thus unaffected by the S alleles. Bk horses and By horses both produce dark pigment. Bk horses have even distribution of pigment, while By horses do not. 7. In guinea pigs, two different genes affect coat appearance. The first gene determines whether hair is produced at all: H is dominant and produces hair, h is recessive and produces no hair. Simultaneously, a second gene determines the color of the hair (if it is produced). CB makes brown hair, CW makes white hair, and CBCW makes tan hair. 8. The black and white pattern in cow’s hides is determined by inheritance of codominant alleles: black (CB) and white (CW), where a heterozygous cow has black and white spots. A CBCW female and a CBCB male mate and produce one male calf. This male calf then mates several years in a row with a single female cow, producing black, white, and spotted offspring in successive years. Determine the genotypes and phenotypes for the calf and his mate 9. One thousand years in the future, mutant humans are living in the subterranean ruins of old New York. The number of eyes the mutants have is determined by an X-linked recessive trait, where XE produces two eyes and is dominant to Xe, which produces one eye. A woman who grew up in an orphanage one day meets a two-eyed woman and a one-eyed man who claim to be her parents. Could they be telling the truth? Determine the possible genotypes of the supposed parents, and determine if, in each case, they could be the parents. 10. In Drosophila, the alleles for cubitus interruptus veins (ci) and sparkling eyes (spa) are 3.0 map units apart on chromosome four. A homozygous cubitus fly is crossed with a homozygous sparkling fly, yielding doubly-heterozygous F1. F1 females are then crossed to doubly-homozygous recessive cubitus, sparkling males to give F2. How many offspring with the phenotype ci, spa do you expect to recover? Assume that you have 1000 total F2 flies.