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"On Urantia there are forty-eight units of pattern control--trait determiners--in the sex cells of human reproduction." (*397)

This quote has disturbed me for some time. On superficial reading it might be construed to be at odds with modern science, if you assume that the trait determiners to which they refer are what we call chromosomes. For we know conclusively that the number of chromosomes in human cells is forty-six. Yet, on further examination of the question, it becomes clear that The Urantia Book's authors have chosen their terminology carefully. In accordance with their restrictions regarding the anticipation of scientific discoveries, they have given us truth without overthrowing accepted "truths" of the day. In order to explain this, let me briefly recount the sequence of events in two converging lines of scientific discovery. The first is the discovery and determination of the number of chromosomes in human cells. Secondly, the discovery of the nature and chemical structure of the genetic material responsible for the transmission of inherited traits, DNA (deoxyribonucleic acid).

First let us look back to the original quote. The use of the term "trait determiners" would seem to suggest that the word "chromosome" might be substituted. The term chromosome is used only once in the book on page 857. The fact that they do not use it here is worthy of note.

Dates of Significance in the Study of Chromosomes

1882 Chromosomes were first seen in human cells by Flemming.

1923 Painter claimed the number of chromosomes in human cells as 48 (24 pairs).

1956 Tijo & Levan establish the chromosome number in human cells as 46 (23 pairs).

Chromosomes are known to carry the genetic material (trait determining substance), or genes. Genes are now known to be strands of DNA. Let us look briefly at some milestones in the DNA story.

Dates of Significance in the Study of DNA

1869 Meischler extracts "nuclein" (DNA) from living cells.

1944 Avery, McLeod and McCarthy identify DNA as the "transforming principle" in pneumococcus type III (the genetic material).

1953 Watson and Crick discover the chemical structure of DNA.

1960 to present Elucidation of genetic code and gene action.

In the discovery of the structure of DNA, important clues to DNA's characteristics were accounted for. Its ability to make copies of itself and carry coded information directing the production of substances, such as proteins, were explained by the "double" nature of the DNA molecule and the nature of the building blocks called nucleotides, which make up the large DNA molecule. Without deteriorating into a lecture in advanced biochemistry (you say it's too late!), please accept that a single molecule of DNA is really composed of two strands, each of which is capable of carrying unique coded information for the determination of specific genetic traits. Thus, a molecule of DNA actually represents two trait determining structures.

Now, back to chromosomes. The chromosomes in non-sex cells of humans occur in 23 pairs (46 chromosomes). Females have 22 pairs of chromosomes, called autosomes, plus a special matching pair of chromosomes, which are important in the determination of gender, the X chromosomes. Males have the same 22 pairs of autosomes, but their chromosomes for gender determination consist of an X chromosome (like those in the female) and a smaller chromosome called Y. In the process of reproduction, special cells are produced in males and females. Males produce sperm cells and females produce egg cells, or ova. The chromosomal makeup of these cells is interesting. Each sex cell from each parent contains only one member from each pair of chromosomes. Therefore, in ova or egg cells there are 22 autosomes plus an X chromosome. There are two types of sperm cells, each type carrying 22 autosomes plus a gender-determining chromosome, i.e., X or Y.

Summary

Now we are about to tie this together. One more piece of information needs to be established. A chromosome contains one molecule of DNA. There are 24 different chromosomes in humans. The 22 autosomes, the X and the Y. If each chromosome contains one molecule of DNA, which we said earlier represents 2 trait determiners, then we have: 24 chromosomes times 2 trait determiners per chromosome = 48 trait determiners in sex cells of human reproduction. The fact is that no single sex cell contains all 48 trait determiners. There do exist 48 trait determiners in the sex cells of human reproduction.

Note that the accepted chromosome number for humans in 1935 was forty-eight. The role of DNA in trait determination was as yet unknown. The authors were able to present us with information which was consistent with the accepted scientific truth of the day in which it appeared and also remained consistent in the light of new discoveries.