Question

Which of the following statements about the mammalian blastocyst is not true?
A) The trophoblast gives rise to the embryo proper.
B) Maternal genes are expressed during cleavage.
C) The blastocyst implants in the mother's uterus.
D) Early mammalian development is slow.

Answer 1

Hint: Initially, the zygote forms a group of cells. Afterward, it develops into a hollow ball of cells known as a blastocyst. The blastocyst grows into an embryo linked to a placenta and surrounded by fluid-filled membranes inside the uterus, where it implants in the uterine wall.
The trophoblast creates the placental portion of the foetus in the mammalian blastocyst. The embryo is a disc-shaped part of the inner cell mass encircled by the trophoblast.

Complete Step by Step Answer:
The transition from the morula to the blastocyst is marked by the appearance of a fluid-filled inner cavity and is accompanied by cellular differentiation: the surface cells develop into the trophoblast (and give rise to extraembryonic structures, including the placenta), and the inner cell mass develops into the embryo.
The outer trophoblast, which symbolises the future tissue contact between the embryo and mother, and the inner cell mass, from which the body of the embryo proper originates, make up the blastocyst until the time of implantation.
Maternal genes are those that create RNA or proteins that are present in the oocyte, the fertilised egg, or the embryo before the expression of zygotic genes begins.
Hence, option A is the correct answer.

Note:In the majority of higher plants, the zygote divides asymmetrically to produce an embryo that is divided into the embryo proper and the suspensor, two areas with different developmental destinies. Following seed germination, the embryo proper divides into areas that allow the development of the following plant generation.