Gene expression in interspecific hybrids. I. DNA synthesis in the lethal cross Arbacia lixula male X Paracentrotus lividus female.

The technique of molecular hybridization has been used to determine in what proportion the DNA's of paternal and maternal origin are present in the lethal hybrid obtained by fertilizing the eggs of the sea urchin Paracentrotus lividus with the sperm of another sea urchin species, Arbacia lixula. The ability of the hybridization technique to recognize DNA molecules from A. lixula and P. lividus was examined and proved to be satisfactory. Labeled DNA's from A. lixula and P. lividus were found to hybridize respectively ten and seven times as well with DNA of their own species as with DNA of the other species. Labeled DNA from arrested hybrid embryos hybridized 1.7 times to twice as well with P. lividus as with A. lixula DNA. We conclude that the interspecific hybrid contains about 2.5 times as much DNA of maternal origin as DNA of paternal origin. The lower content of A. lixula DNA probably results from a partial elimination of the paternal chromosomes during the late cleavage stages.