White (w) coat color in guinea pigs is recessive to black (W). In 1909, W. E. Castle and J. C. Phillips transplanted an ovary from a black guinea pig into a white female whose ovaries had been removed. They then mated this white female with a white male. All the offspring from the mating were black in color…
A) Explain results of this cross.
B) Give the genotype of the offspring of this cross.
C) What, if anything, does this experiment indicate about the validity of the pangenesis and the germ-plasm theories discussed in Chapter 1?
A) Although the white female guinea pig gave birth to the offspring, her eggs were produced by the ovary from the black female guinea pig. The transplanted ovary produced only eggs containing the allele for black coat color. Like most mammals, guinea pig females produce primary oocytes early in development, and thus the transplanted ovary already contained primary oocytes produced by the black female guinea pig.
B) The white male guinea pig contributed a w allele, and the white female guinea pig contributed the W allele from the transplanted ovary. The offspring are thus Ww.
C) The transplant experiment supports the germ-plasm theory. According to the Germ-Plasm Theory, only the genetic information in the germ-line tissue in the reproductive organs is passed to the offspring. The production of black guinea pig offspring suggests that the allele for black coat color was passed to the offspring from the transplanted ovary in agreement with the germ-plasm theory. According to the pangenesis theory, the genetic information passed to the offspring originates at various parts of the body and travels to the reproductive organs for transfer to the gametes. If pangenesis were correct, then the guinea pig offspring should have been white. The white-coat alleles would have traveled to
the transplanted ovary and then into the white female’s gametes. The absence of any white offspring indicates that the pangenesis hypothesis is invalid.