Genetics - Dihybrid Crosses
1. In guinea pigs rough and black are dominant. A rough-coated black guinea pig whose mother was smooth and whte, is mated with a smooth white animal. What kinds of offspring should they produce and in what relative number?
2. A rough, black guinea pig bred with a rough white one gives 28 rough, black; 31 rough, white; 11 smooth, black; and 9 smooth, white. What are the genotypes of the parents?
3. Two rough, black guinea pigs when bred together have two offspring, one of them rough, white and the other smooth, black. If these same parents were to be bred together further, what offspring would you expect from them?
4. Red eye is dominant over brown eye and straight wings are dominant over curved wings in Drosophila. Mating a red-eyed fly with curved wings and a brown-eyed fly with straight wings yields a F1 all red-eyed and straight wings. What kinds of flies would you expect in the F2? In what relative numbers?
5. Pigmented ocelli is dominant over white ocelli in Drosophila.. A certain brown-eyed fly with pigmented ocelli is mated with one having red eyes and white ocelli, and some of their offspring have brown eyes and white ocelli. What are the parental formulas?
6. In Drosophila, gray body is dominant over ebony, and straight wings dominant over curved. A certain gray-bodied, curved-winged female is mated with a gray straight winged male and they produce some ebony-curved offspring. What other kinds of offspring should they produce and in what proportions?
Assume that brown eyes (B) are dominant over blue (b); and right-handedness (R) is dominant over left-handedness (r).
7. A right-handed, blue-eyed man whose father was a left-handed man marries a left-handed, brown-eyed woman from a family in which all the members have been brown-eyed for several generations. What offspring may be expected from this marriage as to the two traits mentioned?
8. A brown-eyed, right-handed man maries a blue-eyed, right-handed woman. Their first child is blue-eyed and left-handed. If other children are born to this couple, what will probably be their appearance as to these two traits?
9. A right-handed, blue-eyed man maries a right-handed, brown-eyed woman. They have two children, one left-handed and brown-eyed and the other right-handed and blue-eyed. By a later marriage with another woman who is also right-handed and brown-eyed, this man has nine children, all of whom are right-handed and brown-eyed. What are the genotypes of this man and his two wives?
In Jimson weeds, purple flower color (P) is dominant over white (p); and spiny pods (S) is dominant over smooth pods (s).
10. A smooth, purple Jimson weed plant crossed with a white, spiny one gives 320 purple, spiny and 312 purple, smooth. If these two types of offspring are bred together, what will their offspring be like, both as to appearance and as to genotype?
11. Make the following crosses in Jimson weeds: A) homozygous purple, spiny with white smooth, and B) homozygous purple, smooth with white, smooth. C) Cross F1 of cross A with F1 of cross B. What will be the ratio of phenotypes of their offspring?