Question

cloning show the genetic variation justify the answer with example​

Answer 1

Reproductive cloning is defined as the deliberate production of genetically identical individuals. Each newly produced individual is a clone of the original. Monozygotic (identical) twins are natural clones. Clones contain identical sets of genetic material in the nucleus—the compartment that contains the chromosomes—of every cell in their bodies. Thus, cells from two clones have the same DNA and the same genes in their nuclei.

All cells, including eggs, also contain some DNA in the energy-generating “factories” called mitochondria. These structures are in the cytoplasm, the region of a cell outside the nucleus. Mitochondria contain their own DNA and reproduce independently. True clones have identical DNA in both the nuclei and mitochondria, although the term clones is also used to refer to individuals that have identical nuclear DNA but different mitochondrial DNA.

Two methods are used to make live-born mammalian clones. Both require implantation of an embryo in a uterus and then a normal period of gestation and birth. However, reproductive human or animal cloning is not defined by the method used to derive the genetically identical embryos suitable for implantation. Techniques not yet developed or described here would nonetheless constitute cloning if they resulted in genetically identical individuals of which at least one were an embryo destined for implantation and birth.

The two methods used for reproductive cloning thus far are as follows:

• Cloning using somatic cell nuclear transfer (SCNT) [ 1]. This procedure starts with the removal of the chromosomes from an egg to create an enucleated egg. The chromosomes are replaced with a nucleus taken from a somatic (body) cell of the individual or embryo to be cloned. This cell could be obtained directly from the individual, from cells grown in culture, or from frozen tissue. The egg is then stimulated, and in some cases it starts to divide. If that happens, a series of sequential cell divisions leads to the formation of a blastocyst, or preimplantation embryo. The blastocyst is then transferred to the uterus of an animal. The successful implantation of the blastocyst in a uterus can result in its further development, culminating sometimes in the birth of an animal. This animal will be a clone of the individual that was the donor of the nucleus. Its nuclear DNA has been inherited from only one genetic parent.

The number of times that a given individual can be cloned is limited theoretically only by the number of eggs that can be obtained to accept the somatic cell nuclei and the number of females available to receive developing embryos. If the egg used in this procedure is derived from the same individual that donates the transferred somatic nucleus, the result will be an embryo that receives all its genetic material—nuclear and mitochondrial—from a single individual. That will also be true if the egg comes from the nucleus donor's mother, because mitochondria are inherited maternally. Multiple clones might also be produced by transferring identical nuclei to eggs from a single donor. If the somatic cell nucleus and the egg come from different individuals, they will not be identical to the nuclear donor because the clones will have somewhat different mitochondrial genes [ 2; 3]

• Cloning by embryo splitting. This procedure begins with in vitro fertilization (IVF): the union outside the woman's body of a sperm and an egg to generate a zygote. The zygote (from here onwards also called an embryo) divides into two and then four identical cells. At this stage, the cells can be separated and allowed to develop into separate but identical blastocysts, which can then be implanted in a uterus. The limited developmental potential of the cells means that the procedure cannot be repeated, so embryo splitting can yield only two identical mice and probably no more than four identical humans.

The DNA in embryo splitting is contributed by germ cells from two individuals—the mother who contributed the egg and the father who contributed the sperm. Thus, the embryos, like those formed naturally or by standard IVF, have two parents. Their mitochondrial DNA is identical. Because this method of cloning is identical with the natural formation of monozygotic twins and, in rare cases, even quadruplets, it is not discussed in detail in this report.