Wednesday, February 26, 2014

No Mitosis without Meiosis

For animals and plants, including humans, cell division resulting from mitosis results in growth, repair, and renewal of the body and its tissues. Our posts have recently discussed gestation--prenatal events up until birth. During this interval mitosis produces startling growth of body mass. A body cell may duplicate itself in 24 hours. Growth multiplies geometrically during gestation from the initial production of the diploid zygote following fertilization. Over 200 different types of body cells are built coherently into the human frame. The construction activity taking place in the body during gestation is a source of wonder and awe, not to mention the growth, repair, and renewal of body tissue for the remainder of one’s life following birth.

We focus on another term equally familiar to students of biology. The term is meiosis. Our study of meiosis reveals significant differences from mitosis. Both terms involve division of cells. Mitosis results in the generation of all the somatic cells of our body, every body cell, and the transmission of all genetic information passed on by the DNA contained in each cell. Both mitosis and meiosis transmit genetic information as body cells divide. Mitosis is linked primarily with growth, while meiosis is associated with reproduction of an entirely new organism. Mitosis is a continuous lifetime event. For the origin of any one organism, however, meiosis is a once in a lifetime event.

Events of meiosis differ from mitosis. After mitosis, the two daughter cells produced are identical to the original cell and have received the same DNA. Two resulting diploid cells are genetically identical. Growth is the outcome of this cell division process. In contrast, meiosis results in production of a new organism. The first step replicates the DNA in maternal and paternal pairs of chromosomes. Two separate divisions follow--meiosis I and meiosis II. First, each pair of chromosomes separates. The second division separates each pair again into haploid sister chromatids. These are unreplicated cells, two maternal and two paternal cells. These four daughter cells have only half as many chromosomes as the parent cell and each is genetically distinct from each other and from the parent cell. The full number of chromosomes is restored when the zygote forms at fertilization.

Because each daughter cell is genetically distinct, no two humans alive (except identical twins) are exactly alike. God apparently endows each member of humanity with uniqueness. A new life is formed by the joining of female and male gametes, ova and sperm, formed in the manner described above. Thereafter, mitosis generates all the somatic cells of the body.

We conclude this series of posts on prenatal events with a personal expression of worship. A recent conversation with a director of our local pro-life pregnancy center triggered a thoughtful perspective on this breathtaking process. Recently refined ultrasound technology for viewing the developing physical child supplements the knowledge we have gained about cellular growth and organ building processes during gestation in the womb of the mother. We know intricate detail about the growth process of mitosis as well as how male and female gametes are formed during the reproductive process of meiosis. Viewing ultrasound images of the forming baby including its beating heart is wonderfully effective in dissuading prospective mothers from terminating the lives of their unborn children. Beyond the ultrasound, there are more rewards for our inquiry: discovery of the microscopic and molecular reality of gametes, chromosomes, and DNA molecules, not to mention how life development processes occur. The beauties of God’s gift of life come ever more clearly into focus.

As we examine the multifaceted panorama of life itself we find it difficult to deny the exquisite signature of the Master Designer. Prospective mothers and every discerning living person should be loathe to deny that signature. The more we understand how our lives unfold from formation of a one celled zygote to our days of maturity and decline, the more we exult in the beauty and love of our Creator.