Question

The technique by which "Dolly" the sheep obtained is termed as
A. Cloning by zygote transfer B
B. Cloning by nuclear transfer
C. Cloning without the help of gametes
D. Cloning by tissue culture of somatic cells

Answer 1

Hint: The sheep was cloned from a diploid cell. The somatic cell from the parent sheep was taken and the nucleus from the diploid cell was injected into the egg cell which was cultured and transferred into the surrogate mother.

Complete answer:
Cloning is the process of obtaining an identical copy of an organism from a parent organism. A clone also refers to an organism that has the exact genetic makeup of a parent organism. Plants and other invertebrates can be cloned in the sense we can obtain genetically identical offspring. Whereas cloning in higher organisms is much more complex.

However, in 1996, a sheep named Dolly was cloned using the techniques of somatic cell nuclear transfer. Nuclear transfer is a technique of cloning where the nucleus of a somatic cell is injected into an unfertilized egg. The process initially involves the extraction of an oocyte. The unfertilized egg cell is first treated to remove the genetic material within it. Once the DNA within the unfertilized egg is removed a diploid somatic cell is extracted from anywhere in the body. The nucleus of the somatic cell is extracted and transferred into the DNA removed, unfertilized egg cell.

In rare instances, the inserted nucleus starts dividing and when placed in the uterus can implant and develop into a complete organism. This is how Dolly the sheep became the first animal to be cloned using the somatic cell nuclear transfer method. The major issue with this technique is that it has a very low success rate and poor efficiency. The nuclear-transferred cell rarely divides and even if it did it rarely implants on the uterus.

Therefore, the correct option is B.

Note: Cloning by zygote transfer is not an actual cloning method, it is a technique used to breed cows and other cattle. Zygote transfer refers to when a fertilized zygote is transferred into a uterus. This is also seen in cases of IVF treatments in humans. Cloning without the help of gametes is very ambiguous and can refer to several techniques but none of which include cloning. The use of tissue culture and somatic cells for cloning is done in the case of plants where vegetative parts of the plant can be used to develop a new plant with the same genetic makeup but cannot be used for animals like sheep.