In this article, we are going to discover chromosomes and why they go to so much trouble in the process of heredity.
Previously, I discussed how the origin of species is tied to the origin of traits. At least, that’s the theory. You can read that article, here. Currently, we are on the path to discover why unit factors (dominant and recessive traits) behave the way they do.
To help you understand this process a little easier, I will preface by saying that chromosomes are found in the nucleus of a cell, which contains DNA. DNA has been discovered to hold the blueprint for life and its traits.
This article is not exhaustive in describing the discovery and process of how DNA functions on a microscopic level. But my intent is to introduce how the diversity of people groups is possible as we continue this journey of discovering the world and how it is today, geographically, linguistically, and religiously.
For a more complex discovery of DNA and the process of heredity, check out the book The New Origin of Species by Nathaniel T. Jeanson. He describes in detail how the physical basis of heredity, the secret of life, has been solved.
Cell Division and the Appearance of Chromosomes
Gregor Mendel’s rules for heredity predicted how traits interact and combine, but his predictions didn’t reveal whether the rules could change. Several decades after Mendel’s death, somatic cells were meticulously observed during what is called cell division. This 7-step process of cell division is termed mitosis.
If you need a refresher on Mendel’s rules of heredity, check out my previous article, here.
Both plants and animals go through this process of mitosis. The way it works is before the nucleus breaks down, structures that look like flexible noodle (chromosomes) appear for a moment in what’s called prophase (see Figure 1). When the membranes surrounding the nucleus breaks down, it has reached the prometaphase.
Within metaphase, the chromosomes line up in the center of the cell. The chromosomes look like “X” shaped structures and represent two identical (replicated) chromosomes that are still partially joined.
In anaphase, the replicated chromosomes are separated from one another and pulled toward opposite ends of the cell. By telophase, the cell starts to split into two cells. Each forming cell contains a chromosome content identical to the other cell. The nuclear membrane begins to reappear in the newly formed cells. Upon completion of the splitting process, the cells have reached the cytokinesis stage.
Why Is This Important?
That is quite the complicated process for a cell to maintain its information. The complexity of nuclear division suggests that chromosomes have a functional role when it comes to heredity. Why else would a cell go to so much trouble to replicate itself and pass on its information?
It is important to note that this process of mitosis is done by nonreproductive cells. This process is just the beginning to answering the question of inheritance.
Meiosis and the Distribution of Chromosomes
In the early 1900s, the American scientist Walter Sutton provided the documentation for a process called meiosis. This process demonstrates the behavior of reproductive cells known as germ cells or gametes — sperm and egg. Mitosis and meiosis are similar in many ways, but meiosis contains some key differences. However, in both processes, the chromosome number and behavior are very predictable.
Sutton observed that the chromosomes occurred in recognizable pairs during the process of meiosis. For example (Figure 2), for each long X-like structure, there exists another long X-like structure. The same is true for a short X-like structure. These X-like structures are technically two chromosomes with one being a replicated copy of the other.
These pairs of chromosomes are separated during meiosis. Each individual chromosome in the X-like structure is distributed among the various products of spermatogenesis and oogenesis. In other words, this is the process that gives rise to sperm and egg.
The Process of Meiosis in Reproductive Cells
As Sutton suggests, one member of each chromosome pair is ultimately maternal in origin and the other, paternal. This makes sense if we look at the chromosome numbers and arrangement (Figure 2). Each pair of chromosomes would be from each parent and would segregate with each new cell containing one individual maternal and paternal chromosome out of each pair.
“Since chromosomes physically segregate from one another during the formation of sperm and egg, perhaps chromosomes contain the unit factors which segregate over successive generations.”
“Replacing Darwin” – by Nathaniel T. Jeanson, pg. 23
If we treat chromosomes as the repositories for unit factors, Mendel’s findings make sense. According to Figure 2, each gamete would produce four reproductive cells with individual chromosomes. Upon fertilization, each reproductive cell would have different varieties of traits, while retaining some of each parent’s dominant and recessive traits. This is why a child could look more like one parent than the other depending on which dominate or recessive traits the offspring receives. It is also why each child can differ from its sibling.
Based on the number of chromosomes in a species, the combinations and results produced is mind-boggling. Take for example Sutton’s published table of theoretical numbers for chromosome combinations. Each are from varying creatures with different numbers of chromosomes.
In humans there are 46 chromosomes, which offers a baffling number of possible trait combinations. These combinations are what bring such diversity and uniqueness between people groups. Diversity, at least, in terms of skin tone, eye shape and facial structure, as well as size and abilities of the body (just to name a few).
Ending Thoughts
This knowledge is by no means exhaustive when it comes to chromosome DNA and the distribution of traits. In fact, that barely scratches the surface. Chromosomes are far more complex in their make-up. You can continue to observe the two major biological molecules that make it up by studying protein and deoxyribonucleic acid (DNA). Which is fascinating!
However, this information I provided helps us understand how we can get such diversity among people as we observe migration patterns after the Tower of Babel in Genesis 11.
Next time, we will take a look at the story of the Tower of Babel and observe the begins of how the world’s nations are divided in their current countries and languages, today.
Don’t forget to check out these books from Answers in Genesis as we begin to shift our focus from microbiology to anthropology, geography, and linguistics. Note, these are Amazon links which I receive a commission if you choose to support this journey and purchase something through the links.
Blessings!
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