Kritika G.

Artificial vegetative propagation is the deliberate production of new plants from parts of old plants by humans. This can be done by following three methods:

1. Cutting: The part of the plant which is removed by cutting it from the parent plant is called a "cutting". In this method one year old stem of root is cut from a distance of 20 to 30 cm. and is buried in the moist soil in natural position. After sometime, roots develop from this cutting and it grows into a new plant. This method is commonly used in rose and sugar cane.

2. Layering: This method of vegetative propagation is used in those plants whose soft branches occur near the ground such as jasmine plant. In this method, a branch of the plant which is near to the ground is pulled towards the ground and a part of this branch is covered with moist soil leaving the tip of this branch above the ground. After sometime, roots develop from that part of the branch which was buried in the soil. This branch is then cut of along with the roots from the parent plant and develops into a new plant. This method of asexual reproduction is also used in the production of plants such as Bougainvillea, jasmine, guava, strawberries, lemon, China rose etc.

3. Grafting: In this method of vegetative propagation the stems of two different plants are joined together so as to produce a new plant containing the characters of both plants. Out of the two plants one plant has a strong root system while the other has a better flower or fruit yield. The plant of which the root system is taken is called "stock", while the other plant of which the shoot is selected is known as "scion"  or "graft". These two stems i.e. the stock and the scion are fitted together by making slanting cuts in them and bound tightly with a piece of cloth and is covered with a polythene sheet. While joining the scion with the stock care should be taken that the diameter of the stock and scion chosen for grafting should be equal. Scion gets the mineral and water from the soil through the stock and develops branches and produce fruits. This method of propagation is used in mango, apple, rose, banana, pear, grape, pineapple and peach.

There are four stages of human embryo after fertilization:

1. Blastocyst Development: Soon after fertilization, the embryo is created from a small group of cells that are constantly dividing inside of a complex structure called the blastocyst. It is formed by two groups of cells, inner and outer cells, and fluids. The blastocyst stays inside a protective cover during maturation called zona pellucida, which could be described as an egg shell. The outer cells are located right below this cover, which will create the future placenta and surrounding tissues to support fetal development in the uterus. The inner cells of the blastocyst will become the different tissues and organs of the human body, such as bones, muscles, skin, liver, and heart.

2. Blastocyst Implantation: When the blastocyst reaches the uterus it implants in the endometrium, the mucus membrane which lines the uterus. The external cells of the blastocyst and the uterine inner lining, together, will create the future placenta. The placenta is a structure that transfers nutrients to the baby and removes his/her wastes.

3. Embryo Development: As the blastocyst reaches the final steps in the implantation process into the inner lining of the uterus, it evolves into a structure called an embryo. This is the time when internal organs and external structures develop. The mouth, lower jaw, throat are emerging, while the blood circulation system starts its evolution and a heart tube is created. The ears arise and arms, legs, fingers, toes, and eyes are being shaped. The brain and the spinal cord are already formed, while the digestive tract and sensory organs start their development. The first bones are replacing the cartilage. After ten-twelve weeks of pregnancy, the embryo moves into the final stage of development, a fetus.

4. Fetal Development: By the twelfth week of fertilization the embryo moves into the final stage of development called the fetal stage. By now, the fetus has formed all of the organs and structures necessary for a baby, but those organs still need to grow and develop.

Meiosis: It is a specialized type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them. Reduction division: The first cell division in meiosis, the process by which germ cells are formed. In reduction division, the chromosome number is reduced from diploid (46 chromosomes) to haploid (23 chromosomes). Also known as first meiotic division and first meiosis.