Chapter 15, Problem 16P

Suppose you are examining a newly found plant species, and you want to determine whether the inheritance of mtDNA is maternal, paternal, or biparental. You find that in the population two variants of mtDNA exist that can be distinguished by size differences of PCR amplification products made with a particular pair of primers. You first perform PCR analysis on DNA isolated from a leaf on each of two individual plants. Then you cross eggs from plant 1 with pollen from plant 2, obtain four seedlings, and perform PCR analysis with DNA from each of the whole seedlings. The results are shown below.

a.	Assuming plant 2 is homoplasmic, do these results exclude any of the three possible models for the inheritance of mtDNA in this species (maternal, paternal, or biparental)?
b.	What experiment could you perform to distinguish between the models that remain?
c.	What experiment(s) could you perform to check your assumption that plant 2 is in fact homoplasmic? Why is such an experiment necessary to make a conclusion about the mode of inheritance of mtDNA in this species?
d.	Explain the differing proportions of the two forms of mtDNA in the four seedlings. Be as specific as possible.