In the mid-20th century, biologists found that linear sequences of genes located on specific sites of chromosomes are what drive the laws of inheritance. Here is one example: 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. Of course, chromosomal inheritance affects much more than just eye color.
It affects everything from physical features to behavioral predictors. The chromosomal theory of inheritance allows for a very basic, unified theory of genetic material being passed from one generation to the next. Each baby born has 23 chromosomes from each parent for a total of 46. From this comes the straightforward idea that genes from those chromosomes carry the genetic material called DNA, or more frequently just called genes.
One fundamental truth about the chromosomal theory is that it connects all biological life. That DNA changes very slowly over time and traits are passed on confirms what Darwin suspected. The farther back in time one goes, the more distantly related all animals, and even plant life, are to human beings. 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, and skin color, too, it is the amount of melanin genetically encoded that makes for such variation.
The mechanism behind Mendelian laws pointed to the chromosomal theory. After Mendel, but before Sutton and Boveri, the noted discoverers of chromosomal inheritance, the work of Walther Flemming and August Weismann had a major impact. It had shown that inheritance could not be explained through meiosis (cell division) alone. It is the recombination produced which allows a wide range of inheritable variation that moves through the long chain of inheritable traits.
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 of the biosphere pageantry called life.
All biodiversity encourages a multitude of many different organisms to evolve. Chromosomal inheritance is just one tiny fragment that affects how genes move from parents to children, and ultimately from species to species.