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.
