Anatomy and Physiology
Quiz 20 :
Development and Inheritance
Differentiation is the mechanism for development. Differentiation occurs from fertilization until birth. All cells contain the same sets of chromosomes. However, cells are not alike at the completion of differentiation. Different organs have different types of tissues. Thus, Different organs have different cells. These different cells contain the same chromosomes and genes. However, the functions of different types of cells are different. Differentiation causes the cells to be different. During differentiation, some genes are turned on. Some genes are turned off. The types of genes being turned on determine the functions and purposes of the cells. Consequently, different sets of genes are active in different type of cell. Therefore, differentiation allows cell to specialize in specific function.
Gestation begins at fertilization. Gestation continues until the fetus is expelled out of the woman's uterus. During gestation, the fetus develops its organs and organ systems. In addition, the fetus grows in size and weight. Thus, gestation is the period of prenatal development. Prenatal development or gestation is divided into three trimesters. Each trimester lasts three months. The three trimesters are known as the first trimester, second trimester, and third trimester. At the end of the second trimester, the fetus's organs have the essential components. The fetus continues to grow and develop during the third trimester. The third trimester is marked by rapid increases in fetal weigh. Therefore, gestation includes the first trimester, second trimester, and third trimester of prenatal development. Hence, (1) matches with (g) 'time of prenatal development.'
Development includes both mitosis and differentiation. The fertilization of an egg and a sperm results in an embryo. This embryo starts out as a diploid cell. This embryonic cell divides into many cells. Thus, development begins at fertilization or conception. The embryo would continue to develop. There are two stages of development. The two stages of developments are prenatal development and postnatal development. Prenatal develop occurs from conception until birth. Postnatal development occurs after birth until the person reaches maturity. Prenatal development is the period cells are divided into many cells. In addition, prenatal development is the time cells differentiate into specialize cells. As cells grow in number, they turn some genes on. The cells turn some genes off. That is, the cells take a specific function and role relative to the other cells. Consequently, some cells become brain cells. Other cells become muscle cells. Postnatal development occurs after birth. At birth, most cells are differentiated. However, not all cells exhibit their full functions and capacity. Development continues from birth until maturity. Cells undergo mitosis. The cellular division causes increase in the number of cells. Thus, the person grows in size. During this period, the specialized cells express their functions. As a result, the person develops sexual or visible reproductive characteristics. At maturity, development ceases. Development enables a single-celled embryo to become an organism. An organism has many cells and different structures. Thus, development consists of mitosis and differentiation. Cellular divisions increase the size of the organism. Differentiation gives rise to different structures.
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