Answer:
meiosis
Explanation:
Down syndrome is an abnormality that occurs on chromosomes 21, it occurs because chromosomes 21 cannot be separated in meiosis, the pair of chromosomes 21 do not separate and go together to one of the daughter cells. In this way, the oocyte or the resulting sperm will have 24 chromosomes instead of 23. When in conception that oocyte or sperm joins the germ cell of its partner that contributes the 23 chromosomes, the total sum of chromosomes that will have the first cell of the new conceived being will be 47.
The initial stages of human embryogenesis.
8-cell embryo, at 3 days.
Blastocyst with an inner cell mass and trophoblast.
Trophoblast differentiation.
Histogenesis of the three germ layers.
Artificially colored - gestational sac, yolk sac and embryo (measuring 3 mm at 5 weeks)
Embryo attached to placenta in amniotic cavity.
Answer:
The nucleus contains the protons and neutrons which takes up most of the mass of the atom.
