Question

1. A. What is parthenogenesis? How does this seems to occur in birds? What is the main barrier to this happen in mammals? How could parthenogenesis be engineered in mammals?

B. What would be needed to regrow a human limb in the lab to later be transplanted on an amputee?

Answer 1

Answer of the 1st part of the question no 1.A.

When an unfertilised egg(ovum) undergoes embrayonic development and can produce new offspring ,then this process is called parthenogenesis. It is a type of asexual reproduction.It is found in many lower plants,in some invertebrates, and in some vertebrates like birds.

Answer of the 2nd part of the question no 1.A.

The female bird is diploid(2n) and it produce oogonia. The genotype of oogonia produced by female bird is ZW and oogonia is diploid (2n).Now, this oogonia undergoes meiosis1 to produce primary oocyte(ZW) .Primary oocyte is also diploid (2n).Primary oocyte undergoes meiosis2 to produce the first polar body(Z or W, n ) and secondary oocyte(Zor W, n) .So, now the chromosome present in secondary oocyte is either Z or W. Now, the secondary oocyte undergoes parthenogenic development and will produce eg nucleus (n) and second polar body(n). Now,this egg nucleus and second polar body will fuse to form a parthenogenic offspring (2n). If the secondary oocyte contain the chromosome Z ,the parthenogen produced in this way having chromosome ZZ(2n) will be the male and it will survive whereas if the secondary oocyte contain chromosome W,the parthenogen(WW,2n) produced in this way will die. Thus, parthenogenesis occurs in bird.

Answer of the 3rd part of the question no 1.A.

The main barrier of parthenogenesis to be happened in mammals is genetic imprinting. In case of parthenogenic mammal it will have two sets of imprinted genes from mother but it will not get any imprinted genes from its father .and as a result of this several  abnormalities will develop in that offspring. and ultimately, the parthenogenic mammal will not survive.

Answer of the 4th part of the question no 1.A.

Parthenogenesis could be engineered in mammals by various methods such as by calcium ions microinjection method, treatment by calcium ionophore or by various chemical or electrical stimulations that can start the parthenogenic process.

Answer of the question no 1.B.

Stem cells would be needed to regrow a human limb in the lab to later be transplanted on an amputee.