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DNA, the Brain and Human Behavior

DNA, the Brain and Human Behavior

Is DNA a thing? precisely saying, it is a Package of Information. The gene is a package of information, not an object. The pattern of base pairs in a DNA molecule specifies the gene. But the DNA molecule is the medium, it's not the message. Maintaining this distinction between the medium and the message is absolutely indispensable to clarity of thought about evolution.

Genetics, an introduction:

From the bottom up, it goes like this: There are four compounds: adenosine, thymidine, cytidine, and guanine. These compounds are joined together in base pairs. Adenosine (A) pairs with thymidine (T), and cytidine (C) pairs with guanine (G). The molecular structure for the guanine-cytidine pair is illustrated at right (links to source). These base pairs connect together to form two matched helices, known as deoxyribonucleic acid (DNA). In his book, Evolving Brains (2000), John Allman explains how the code of base pairs is read. A bold emphasis is added to his explanation.

Bonding of DNA base pairs

The code [of base pairs] is read from one direction in one strand. Three-letter sequences, triplets, specify each amino acid, and the sequence of triplets in turn specifies the chain of amino acids that makes up a protein." Allman explains that there are 64 possible triplet sequences. "Each of 61 triplets encodes for one of the 20 amino acids. Thus some amino acids are specified by more than one triplet, although no triplet specifies more than one amino acid. The other three triplets are stop codons that signal the end of a particular protein. The complete sequence of triplets that encodes a protein is a gene.

Configuration of DNA Base pairs

Genes are grouped together in large volumes as chromosomes which are large enough to be seen under a microscope. The image below is a light microscopic presentation of a normal, human male chromosome set (karyogram) from the German Mental Retardation Network (image links to source).

DNA Chromosomes Structure

Other than germ cells, all humans' cells normally contain 46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes—either a pair of X chromosomes in females or an X chromosome and a Y chromosome in males. In each pair of autosomes, one chromosome is inherited from an individual's father and one from his or her mother. When contributions of sex chromosomes proceed normally, the mother contributes an X chromosome and the father contributes either an X or a Y chromosome. Neil Shubin, in Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body (2009), explains that "DNA is peeled into two halves every time a cell divides, and so every chromosome must be teased into two daughter chromosomes at the same time. This peeling also takes place when eggs and sperm are made, and this is how genes are passed to offspring."


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