1. The Ovum (egg). Prior to fertilization. (1 set of chromosomes from mother)
1. The first step of human cloning involves removing the nucleus of a woman's egg. This nucleus contains 1 set of chromosomes from the woman.
2. Fertilization. A sperm cell penetrates the ovum and delivers an additional set of chromosomes from the father. A new life is formed.
2. Next, the researcher isolates a nucleus from a somatic (other than sperm or egg) cell, e.g. a bone marrow or skin cell obtained from a person to be cloned. The donor nucleus is inserted into the egg as shown. The donor nucleus contains both sets of chromosomes.
3. The new embryonic human contains 1 set of chromosomes from the mother and 1 set from the father.
4. During day 2, the human embryo undergoes cleavage, dividing into two cells.
3. A new human being is formed and is genetically identical to the person whose nucleus was used.
5. Each of the two cells divides to yield 4 cells.
4. The embryonic clone divides into two cells through cellular cleavage.
6. The division process repeats and each of the 4 cells divides to yield 8 cells.
5. The embryonic clone continues to undergo cellular cleavage and it compacts forming a morula.
7. Day 3. The embryo continues to divide and becomes compact. When a dozen or more cells are present, the embryo is called a morula (Latin, mullberry)
6. The embryo forms into a blastocyst. The blastocyst contains an outer cell mass (shown as an outer layer of gray cells) and inner cell mass (shown as purple cells. The purple inner region contains the embryonic stem cells necessary for research.
8. Days 4-5. A cavity forms (shown in white) in the cellular mass of the morula and the embryo reaches the blastocyst stage. The blastocyst contains an outer cell mass (shown as an outer layer of gray cells) and inner cell mass (shown as purple cells). The blastocyst implants itself in the wall of the uterus, and the embryo contines to develop.
7. The human embryonic stem cells are then harvested in a process that kills the embryo. The stem cells can then be replicated. These stem cells and all descendent stem cells form a stem cell line. The entire process of producing an embryonic clone is known as SCNT (Somatic Cell Nuclear Transfer) because a nucleus of a somatic (non-sex) cell is transferred to a human egg that has had its genetic material removed.
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Last modified: 4/15/2006
