Which unique feature does a chick embryo possess?

A chick embryo possesses large amounts of yolk, which is a unique feature that sets it apart from mammalian embryos. The yolk serves as the primary source of nutrition for the developing embryo, allowing it to sustain development outside the mother’s body. This is particularly important for species like birds, where the egg must provide all necessary resources until the embryo is ready to hatch.

In avian species, the large yolk is situated beneath the blastoderm—a layer of cells where actual embryonic development occurs. This structure allows the embryo to draw on the extensive nutrient reserves provided by the yolk, facilitating growth during the incubation period. The presence of significant yolk is a defining characteristic of chick embryos and is adapted to their reproductive strategy of laying eggs.

The other choices do not accurately reflect features of chick embryos: a direct connection to the mother is typical of mammals, not birds; a primitive streak is part of early development but is not uniquely proliferative to chicks; and the presence of a blastodisc is essential for chick development, as it is where the embryo forms on top of the yolk.