June 24, 1920] 



NATURE 



531 



his life in Eastbourne, and occupied "Hodeslea," 

 which is now the residence of the Union's treasucer. 

 The house was built by Huxley in 1890 and he lived 

 there until 1895. whilst his widow remained there 

 until her death in 1914. Mr. Adldn has recently 

 placed a bronze tablet on the house relating these 

 facts. 



Genetic Segregation,^ 



By W. Bateson, F.R.S. 



LATER developments of genetics have been, in the 

 main, attempts to discover the nature and scope 

 of segregation. Mendel proved that certain characters 

 are determined by unit-factors. Their integrity is 

 maintained by segregation, the capacity, namely, to 

 separate unimpaired after combination with their 

 opposites. We have been trying, first, to ascertain 

 specifically what characters ' behave in this way, 

 whether there is any limit to the scope of segregation 

 or any classes of characters otherwise transmitted. 

 Among characters known to be subject to segregation 

 are illustrations of most of the features by which 

 plants and animals are distinguished. In regard to 

 two classes of characters the evidence for segregation 

 is, nevertheless, rather noticeably imperfect. No quite 

 clear proof exists that differences in number — tneristic 

 characters in the strict sense — are governed by 

 factors comparable with those that control, for 

 example, colour. The extra toe of the fowl and 

 the single leaflet of the monophyllous strawberry are 

 perhaps the best examples, but reservations may be 

 entertained. Also, though segregation can be demon- 

 strated in regard to quantitative characters, parental 

 tvpes thus distinguished often fail to re-appear, and the 

 inheritance is subject to special complications. 



Groups or complexes of factors are now recognised 

 as sometimes segregating whole. Were it not that on 

 occasion elements of the complex become independent, 

 the group would pass for one unit-factor. The sex- 

 complex is an obvious example. Intermediate flower- 

 colours, like those of modern sweet peas, probably 

 arise by this process. The plausible suggestion that 

 the new terms are only rare cross-overs in a closely 

 linked series does not' fit the evidence. A striking 

 illustration appears in Oenothera, in which, as Renner 

 latelv showed, several groups of characters normally 

 segregate as single factors. These complexes are in 

 several forms not borne equally by the two sexes of 

 the plant, and most of them cannot exist in the 

 homozygous state. By these discoveries the CEnothera 

 problem is greatly elucidated. 



The second question is to determine^ when in the 

 life-cvcles segregation can occur. Admittedly it is a 

 phenomenon of cell-division. If we knew the animals 

 onlv we might confidently adopt the view of Morgan 

 that normal segregation happens during the matura- 

 tion process at the stage of synapsis, when the 

 maternal and paternal chrornosomes are believed to 

 conjugate in pairs. Most of the tacts of linkage may 

 be thus well represented, but the absence of crossing- 

 over in the sex-heterozygote (Drosophila and silk- 

 worm) is not readily explicable, nor is there as yet 

 extensive evidence that the number of linkage-systems 

 agrees with that of the chromosomes — a primary 

 postulate of Morgan's theory. The evidence for an 

 orderlv anastomosis, or even of any exchange of 

 materials between chromosomes, is weak : and the 

 visible features of chromosomes are scarcely sugges- 

 tive of the prodigious heterogeneity requisite. Even if 

 the linkage-systems correspond with the chromosomes, 



1 Abstract of the Croonian L«cture delivered before the Royal Society 

 «n June 17. 



NO. 2643, VOL. 105] 



which is a most attractive conjecture, exchange of 

 material between chromosomes need not be essential 

 to crossing-over. It may be doubted, however, 

 whether the general course of cytological evidence 

 does not point to the rSle of the chromosomes being 

 rather passive than active. 



That in plants segregation even in its normal 

 course is not limited to the reduction-division is now 

 certain. In Matthiola, Campanula, Begonia, and 

 Oenothera the genetic composition of the male and 

 female organs may be normally different, and segrega- 

 tion cannot have happened later than the constitution 

 of these organs. This kind of segregation must 

 result in Campanula carpatica (experiments of 

 C. Pellew) and in Begonia Davisii from the peculiar 

 genetic properties .of the female complex, for it re- 

 i^ppears in offspring derived from the female side for 

 several generations at least, but not among those 

 derived from the male side. Collins's evidence from 

 Funaria proves further that sex-segregation may 

 happen during the growth of a haploid form. 



Periclinal chimaeras and the production of distinct 

 types from adventitious buds prove that segregation 

 rnay take place during somatic development, 

 whether in the differentiation of the layers or of the 

 root. In the genetic properties of the tare-like rogues 

 of peas there are features which not only illustrate 

 the occurrence of gradational change in genetic pro- 

 perties, following somatic differentiation, but also 

 show that this gradation affects the male and female 

 organs differently. From these facts it must be con- 

 cluded that normal and orderly segregation (apart 

 from chance sporting) can occur at various cell- 

 divisions, and not exclusively at reduction. Not im- 

 possibly these somatic segregations may be accom- 

 panied by some visible cvtological differentiation, but 

 that question must not be prejudged. 



Having regard to the fundamental distinctions 

 between the morphological relations of the germ-cells 

 to the soma in animals and in the flowering plants, 

 it is not surnrising that the processes of segregation 

 should be differently effected in these two groups of 

 organisms. 



Colour Index of the British Isles. 



AT a meeting of the Royal Anthropological Insti- 

 tute held on June 15, Prof. Arthur Keith, ex- 

 president, in the chair. Prof. F. G. Parsons read a 

 paper on "The Colour Index of the British Isles." 

 He first reviewed the different ways of constructing 

 an index of nigrescence, and directed attention to what 

 he considered their weak points. Prof. Parsons pro- 

 posed as a simple and workable index that the per- 

 centage in any group of individuals with dark brown 

 and black hair should be added to the percentage with 

 eyes in which any brown pigment is present, and the 

 result divided by two. For practical purposes he 

 found it better to record the percentages of dark hair 

 and dark eyes separately. He then proceeded to 

 examine the' large mass of statistics collected by Dr. 

 Beddoe in the middle of the last century, and pointed 

 out that the first deduction was that women are in 

 the mass darker than men, and that where the people 

 are fairest the difference between the sexes is greatest, 

 as the following table shows : 



In''ex 



No. of records 



niff. 



4 Northern Counties 

 3 Eastern ,, 



2 Western ,, 



M'n Wom»n 



1767 262 33-5 y-."^ 



1563 34-4 38-2 3-8 



4057 45-5 467 1-2 



It therefore became necessary to exclude those 



