Non-Mendelian Genetics Problems
Codominance (Incomplete Dominance) Problems
1. In shorthorn cattle, the gene (R) for red coat color is not dominant over white (R'). The heterozygous combination (R R') produces roan (a blend of the two). A breeder has white, red, and roan cows and bulls. Figure out the phenotypic ratios for the following crosses.
a) red x roan
b) red x white
c) roan x roan
2. A cross of a red flower snapdragon plant and a white flower snapdragon yields 200 pink flowers. When two of these pink flowers are crossed, the F2 includes 25 red flowers, 26 white flowers and 56 pink flowers. What type of heredity appears to be involved? Test your hypothesis by working out the two crosses. Are the Punnett square results as you expected?
3. A cross between a black cat & a tan cat produces a tabby pattern (black & tan fur together). What percent of kittens would have tan fur if a tabby cat is crossed with a black cat?
Multiple Alleles/ Blood Types
4. A student, whose mother has Type AB blood and father has Type O blood, finds out that he is Type AB and states, “I guess when it comes to blood type, I take after my mother.” You are his biology teacher. Why does his statement put you in an uncomfortable position? What would you say to the student?
5. A woman with blood Type B, whose parents were both Type AB, marries a man with blood Type B whose mother was Type AB and father was Type O. Give the predicted phenotypic ratio of the offspring that could be produced by this man and woman.
Other
6. In corn plants, a dominant allele (I) inhibits kernel color, while the recessive allele (i) permits color when homozygous. At a different locus, the dominant gene (P) causes purple kernel color, while the homozygous recessive genotype (pp) causes red kernels. If plants heterozygous at both loci are crossed, what will be the phenotypic ratio of the F1 generation?