HEREDITY.

Dominion, Volume 5, Issue 1392, 19 March 1912, Page 3

HEREDITY.

■ MENDEL'S .THEORY EXPLAINED. ' In connection with the gift (referred to in yesterday's cablegrams) by Capt. Dearst of .£lll,OOO to tho British Board of Agriculture for Jlendelian experiments in improving the breed of steeplechasers tho following statement by Mr. Doncaster "i his book on "Heredity in the Lijjht ot Recent Research" will be of interest-— Johann Gregor Mendel was .i monk of the monastery of Brunn in Bohemia. His most important paper was published in ISGIi, but perhaps owing to tho fact that the biological world was then occupied almost solely with the discussion of Jhe "Orisriu of Species," his work attracted no attention at the time, and only bscame celebrated on its rediscovery in WOO. One cannot avoid speculating on the possible effects on biological thought, had the experiments and conclusions of his now l'nmous contemporary ever co/iie jo the knowledge of Darwin." Tho method which led Mendel to his great discovery wa? to experiment with p.aiiivs exhibit ing , discontinuous character;;, and to consider each (character separately. Previous workers in the samo lielu had made many laborious experiment' in crossing tlifl'crent races of plants or animals, but had always regarded (ha individual as the unit, and hence arose I lie Ijolipi that mongrels or hybrids were usually intermediate between the parent*, resembling ono iu tome features, tho other in others, but with no regular rule; and further, that when hybrids were bred together tho o.Tsnring were often almost infinitely variable, extending in a scries from spmo closely approaching ono original parent through a diversity of intermediate or new forms to others like the Kcond parent. So grew up the belief that tho crossing of distinct races or breeds is a potent cause, of variability, which, however, except when "revcrsio'n on crossing" took place, seemed to fall under _no ascertninable law. Mendel's most important experiments were made with races of tho euiblo pea, which he t'row in tho garden of his monastery. Ho found in peas several characters which vary and are inherited di-can-tinuously. and ho crossed together races which differed in one or more of micli character.?, but in the oll'snrintf and lal t generations he considered the distribution ot each character by itself, quite apart fr m" l'; c ot!,or diameters of (he plant, lhe Mondclifin theory of inheritance, has also teen applied with verv interesting result* to- animals, which tend to s-how that the phenomena aro not rare or excentional, but universally distributed Referring to Mendel's work, Professor J. A. )Thoniso:i writes: Mendel's groat paper, communicated to the Natural History Society of Bnimi, remained practically unknown till ISOO, when ])e Vries in Holland, C'orrcns in Germany, and Tscherinak in Austria independently, nnd almost simultaneously, reached experimental results closely resembling Mendel's. This led to a rediscovery of the buried paper and to a period of very active experiment, in connection with which Bntesou, Castle. Cuenot, nnd their collaborateurs have been especially prominent. Mendel worked chiefly with the edible pea, "Pisum sativum," v;hich has many well-marked varieties and is habitually self-ferlilised. When he crossed a giant variety of six to seven feet with a dwarf variety, J to H feet high, tho offspring were all tall. The character of tallness which appeared in the hybrid generation, to the exclusion of dwarfness, was called by Mendel the; "dominant" character, the other being "recessive." In his exceedingly clear exposition of Mendelism (100"»), Professor R. C. Punnott, himself a productive investigator, stales the_ characteristic Mendelian result thus: "Whernver there occurs a pair of differentiating character?, of which one is dominant to the other, three possibilities exist: there are recessives which always breed true to the recessive character; there are dominants which breod true to the dominant character and aro therefore pure: and thirdly, there are dominants which may bo called impure, and which on self-fertiiisalion (or inbreeding, where the sexes are separate) give both dominant and recessive forms in the fixed proportion of three of tho former to one of the lat(6r."

Professor Biiteson, the leader of the Monilelian school in Britain, tays: "The essential part of the discovery is the evidence that the genm-cclls or gametes produced by cross-bred organisms may in respect of given characters be of the pure lNirentijl types, and "consequently incapable of transmitting the opposite character; Hint when such pure similar cametes are united in fertilisation, *.he individuals so formed and their posterity nre free from all taint of tho. cross; that there may bn, in short, perfect or almost; perfect discontinuity between tlwso genus in respect of o:ie of each pair of opposite character?." This idea of the segregation of tho ilnminaut and the recessive rluiraolrT.s in two dift'eronfc scts of p?rmeells is the essence of Memlelian tlieorv.