Abstract
RECENT results of molecular genetics enable us to estimate the number of human genes, if certain assumptions are made. The following data are available: (1) The α-chain of human hæmoglobin contains 141, the β-chain contains 146 amino-acids, corresponding to a molecular weight of about 17,000 each1. Assuming a triplet code2,3 this means that the α- and β-chains are determined by 423 and 438 nucleotide pairs, respectively. According to ‘Svedberg's law’4, many proteins consist of sub-units of the same order of magnitude (molecular weight of about 17,500). Hence, the assumption seems to be warranted that one average structural geno might have a length of about 450 nucleotide pairs. (2) The weight of one haploid human chromosome set in human spermatozoa is about 2.72 × 10−12 g. Granulocytes contain about 6.23 × 10−12 g; lymphocytes contain about 5.84 × −12 g (ref. 5). Extensive examinations have shown that the DKA. content is constant in all resting cells of one species, which have the same number of chromosome sets, and depends on the degree of polyploidy5,6. The assumption seems to be justified that most of the DNA works as genetic material, even if in some cells minor fractions with other functions might possibly be present7. In the following calculations the total amount of DNA in a haploid human chromosome set is estimated to be about 3 × 10−12 g. (3) Usually the genetic variants of human haemoglobins differ in one amino-acid substitution only1,8. One structural gene can only produce one single type of genetically determined polypeptide chain. As much as we know, this applies for other genetically determined proteins as well. This means that the genetic information for these structural genes can only be present once. Any degree of polyteny for these loci in the germ cells is highly unlikely. As has been mentioned, however, the DNA content of diploid cells is about twice the content of (haploid) spermatozoa. We assume that the total genetic information is only present once.
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VOGEL, F. A Preliminary Estimate of the Number of Human Genes. Nature 201, 847 (1964). https://doi.org/10.1038/201847a0
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DOI: https://doi.org/10.1038/201847a0
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