Prior to 1902, many biologists suspected that chromosomes were responsible for delivery of the genetic materials that every organism has. But it fell to Theodor Boveri and Walter Sutton, working independently, to discover what is now called the chromosomal theory of inheritance. Basically, they found that linear sequences of genes located on specific sites of chromosomes are what drive the laws of inheritance.
If both of one’s parents have blue eyes, both parents carry the right genetic instructions on their chromosomes for producing offspring with blue eyes. But in the case of two brown-eyed parents, their child could still be born with blue eyes if both of them contribute one bit of DNA each which is encoded with the gene for blue eyes from the mother’s and father’s own parents. The result is what often is heard by surprised grandparent’s meeting their new grandchild: “Look, she (or he) has Grampa Robert (or Roberta’s) eyes!”
The chromosomal theory of inheritance allows for a fundamental and unified theory of genetic material being passed from one generation to the next. In modern DNA testing, the linear sequence of just what markers encode upon a strand shows that such patterns of DNA are central to which characteristics the offspring will inherit. The newborn will have twenty-three chromosomes from each parent for a total of forty-six. From this comes the straightforward idea that genes from those chromosomes carry the genetic material called DNA.
There are, of course, many reasons an organism will have one particular eye color. Brown eyes are a more dominant genetic trait than blue eyes. All over the world it can be seen that more human beings inherit brown eyes. The chromosomal theory of inheritance is just one factor in what traits are passed on to each new generation. In the case of eye color, or skin color too, it is the amount of melanin genetically encoded that makes for such variation. In fact, no child’s true eye color can be determined at 100 percent until about age three, when the inherited melanin has more completely produced the amount of pigment the baby has inherited.
The mechanism behind Mendelian laws pointed to the chromosomal theory. After Gregor Mendel, but before Sutton and Boveri, the work of Walther Flemming and August Weismann had shown that inheritance could not be explained through meiosis (cell division resulting in new gametes or spores) alone. It is the recombination produced which allows a wide range of inheritable variation.
In all life, it is variation and thus biodiversity that encourages such a multitude of many different organisms to evolve. Chromosomal inheritance is just one tiny fragment resulting in the biosphere pageantry called life.