Question

Give two differences between a zygote and a foetus.

Answer 1

Both zygote and foetus are the result of sexual reproduction in humans. Zygote formed first and after that foetus is developed in the body of the female. Zygote and foetus developed by the fusion of male and female gametes.

Complete answer:
Zygote: The entry of sperm into the ovum induces completion of the meiotic division of the secondary oocyte.
- Entry of sperm causes breakdown of metaphase promoting factor (MPF) and turns on anaphase promoting complex (APC). This results in completion of meiosis-2.
- The second meiotic division is also unequal and results in the formation of a secondary polar body and haploid ovum. The haploid sperm and ovum fuses together to form a diploid zygote.
- Sperm and ovum contain 23 chromosomes. The fusion of sperm nucleus and egg nucleus makes a zygote that has 46 chromosomes.

Foetus: After implantation, finger-like projections appear on the trophoblast and chorionic villi. Chorionic villi surrounded by uterine tissue and maternal blood.
- The chorionic villi and uterine tissue together form a structural and functional unit between developing embryo (foetus) and maternal body called placenta.
- Placenta is an organ which connects the foetus with the uterine wall. Placenta also acts as an endocrine gland and synthesizes large quantities of proteins and hormones such as hCG and somatomammotropin.
- The umbilical cord connects the foetus to the placenta. During the first trimester, the basic structure of the foetus is formed. This involves cell division, cell migration and differentiation of cells into the many types found in the body.
- During this period the developing baby is known as foetus.

Note: Placenta and umbilical cord are rich sources of stem cells. Stem cells from the placenta are stored and collected in banks. They are the non-embryonic stem cells. The mitosis after the fertilization is the union of their chromosomes.