If the sperm cell fertilises the ovum, and implantation does not occur, then the corpus luteum degenerates and it turns into corpus albicans, stopping progesterone secretion. If fertilisation occurs and implantation also, the syncytiotrophoblast, the "root part" of the blastocyst (one of the early structures originated from the zygote), produces a hormone that is called <span>human chorionic gonadotropin (hCG). The hCG is what makes the corpus luteum keep secreting progesterone and maintain itself. The progesterone will then help keep the endometrium and, therefore, allow the development of the embryo to happen.</span>
The answer is “Variation that decrease reproductive success are more likely to be passed on.”
A metallurgical microscope
A DNA molecule consists of two stands of nucleotides that wind around each other like a twisted ladder with a phosphate and sugar backbone. The nitrogenous bases are divided into two groups called the pyrimidines and the purines. The pyrimidines include the thymine and cytosine, the purines are adenine and guanine. The nitrogenous bases in the double helix are bound together according to the base pairing rule. Adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C). The student either drew the base pairing showing adenine and thymine or guanine pairing with cytosine.
