1908-9.] Mendelian Action on Differentiated Sex. 
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XXXVII. — Mendelian Action on Differentiated Sex. By D. Berry 
Hart, M.D., F.R.C.P.E., Lecturer on Midwifery, Surgeons’ Hall, 
Edinburgh; Carnegie Research Fellow. (From the Laboratory of 
the Royal College of Physicians.) 
(Abstract.) 
It has long been known that the male and the female human genital tract 
contain not only organs characteristic of their sex proper, but also certain 
parts of the opposite sex in a less developed but yet perfectly definite form. 
Thus the female genital tract is made up of, not only its characteristic 
organs, the ovaries, tubes, uterus, etc., but also the epoophoron (parovarium) 
and its duct, the equivalent of the epididymis and ductus epididymis 
of the testis. In the same way, the human male has his characteristic 
sexual organs and also the appendix testis and prostatic utricle, the 
representatives of the fimbriated end of the Fallopian tube and of the 
lower end of the vaginal tract (hymen mainly, but varying). 
The significance of these facts has not been hitherto definitely investi- 
gated, and it occurred to me, in the course of a study of Mendelism in 
relation to the nature of sex, that the genital elements already defined might 
be considered as potent and non-potent, or as dominant and recessive in 
Mendel’s terminology, and as elements on which Mendelian action took place 
and could thus be studied. 
Mendel showed in his variation experiments with the eating-pea, 
that if peas with each one contrasted character,* such as tallness and 
dwarfness, the other characters being common, were crossed, all the 
plants were tall in F 1 , while in the subsequent selfed. generations the tall- 
ness and dwarf ness segregated in the ratio of D : DR : R as 1 : 2 : 1. This 
means that of the plants one quarter bred true to tallness (D), one quarter 
to dwarfness (R), while one half (DR) gave always DR : R as 3 : 1. It was 
found in the crossing experiments that it made no difference in the results 
which plant, tall or dwarf, was used for pollination. 
Mendel described the tallness as a dominant unit-character, D ; the dwarf- 
ness as recessive, R ; while the tall plant giving tails and dwarfs 3:1 is 
termed an impure dominant, DR. 
* Menclel chose seven characters, of which I select the one given above for illustration. 
