Maternal and embryonic contributions to the functional messenger RNA of early development.

Some of the DNA-like RNA synthesized during oögenesis remains available up to early blastula (stage 7). This RNA then begins to disappear from the embryo, so that by early gastrulation half of its sequences have been lost. Total maternal RNA of embryos represents more sequences than can be recovered at early stages from polyribosomes. Some of it must therefore reside in cytoplasmic fractions that do not cosediment with polyribosomes. Most of the maternal DNA-like RNA is eventually translated before it is lost. Messenger RNA transcribed on the embryonic genomes appears very early on polyribosomes and is translated there along with maternal RNA.