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Show 94 MR. W. BATES0N ON COLOUR-HEREDITY [May 25, As we have also seen, the colours taken collectively follow simple expectation ; F ^ F , giving approximately 3 coloured to 1 albino, and Ft x albino giving approximately equal numbers of each. As to the frequencies and valencies of the particular colours nothing can be said with much confidence as yet, beyond the statement that Ft gives off albino gametes about equal in number to the various coloured gametes collectively. In a discussion of this subject, Professor Weld on (25) has suggested that an average of one albino in nine might have been expected. I can see no reason why this proportion should be impossible in nature, from Ft x F r Its occurrence would, however, be remarkable and raise some important problems in gameto-genesis. So far, however, it has not been recorded. Professor Weldon is in error in stating (25. p. 34) that I have already dealt (4. p. 52) with such a case of 1 albino in 9. The case in question was that of Antirrhinum, where de Vries obtained from Fx x Fx four forms in the proportion 9:3:3:1, the one being the white, which therefore occurred in the proportion of 1 in 16. This is the proportion Mendel himself conjectured might be found in a case of resolution, but I do not gather that he had actually observed such a case. N o case of resolution has yet been sufficiently studied for us to speak with any confidence as to the ratios of the gametes or the nature of the process of resolution. Tschermak has had cases of 1 recessive in 4, after resolution. In poultry I have had cases somewhat similar, to be described hereafter. In apparently all recorded cases of resolution some gametes of Ft carry the compound character unresolved. It is not at all easy to suggest a scheme which shall fit both the observed facts of resolution and those of cell-division. For example, suppose the gametes of Fx to be 50 per cent, albino, 50 per cent, variously coloured, if segregation were complete. Let us consider the coloured gametes separately, and for simplicity assume there are only three kinds of them, viz. the unresolved grey, black, and yellow, the two latter being hypallelomorphs of grey. It is then clear that in whatever numbers the three types are each represented, so long as their sum equals the total of albino gametes, there must be more black character in any black gamete, and more yellow in the yellow gamete, than in any grey gamete ; or there must somewhere be a cell-division in which a part of the yellow and a part of the black have been lost. If, for instance, the hybrid bore gametes in the proportions 2 grey (=black-[-yellow), 1 black, 1 yellow, 4 albino, we recognise that unless the blacks and yellows carry double portions of their respective colours, part of the colour originally introduced into Fx has been lost. Such doubling is not altogether inconceivable, though until histological methods are made applicable to these questions of gameto-genesis the possibibity can hardly be tested. W e note as a fact favourable to such a view, that the visible amount of pigment in a black or a yellow zygote is far |
