Vol. 6, 1920 
GENETICS: H. H. LA UGHLIN 
241 
In a parent of the Pi generation, R = 12 — >12, i. e., there is no range 
in the number of chromosomes which the given parent may contribute 
to the Fi zygote; this number is always 12. For all ancestors of the P2 
and all older generations, R = 0 — >ll, except (a) for those ancestors 
from whom an x- or a ;v-chromosome must certainly descend (solid line 
ic-trail or y-trail in chart), in whom R = 1 — ^12; except also {h) for 
those ancestors from whom an :r-chromosome may by alternate chance, 
descend (dotted line ^-trail in chart) in whom R = 0 — >12. 
In a general formula 11 would be substituted for by n, and 12 by w + i, 
with value as in formula 1. 
No. 7. \ : Ct = The probability that one or the other member of each of 
all of the equivalent chromosome-pairs characteristic of the species (i. e., 
an entire chromosome-series excluding the xx and xy pairs), from the 
given ancestor will enter the Fi zygote. 
In the case of ancestors not in the x-trail or the y- trail, such an occur- 
rence is the extreme limit of ancestral influence possible to a given ancestor, 
and its happening precludes any hereditary influence at all on the propositus, 
i. e., the Fi zygote, on the part of any other ancestor of the same paternal 
or maternal half -pedigree, as the case may be, except the lineal ancestors 
and descendants of the given ancestor. 
1:^=1: (2")^-^ 
n = Value as in formula 1. In man n is taken tentatively at 11. 
p = Value as in formula 1. 
No. 8. 1 : or 1 : Cty = The probability that ow^ or ^/^^ o^/z^r member 
of each of the several equivalent chromosome-pairs characteristic of the 
species, and also one x- or one ^/-chromosome, as the case may be, from the 
given ancestor will enter the Fi zygote. (In man this total gametic num- 
ber of chromosomes is taken tentatively at 12.) 
Such an occurrence can happen only in reference to ancestors in the 
X- or 3^-trails, and its happening precludes any hereditary influence at all 
on the propositus, i. e., the Fi zygote, on the part of any other ancestor 
of the same paternal or maternal half-pedigree, except the lineal ances- 
tors and descendants of the given ancestor. 
1 : C,, = (1 : Ci).{l : 
Values of 1 : and 1 : C^^ as in formulas 5 and 7. 
1 : C,, = (1 : Q.(l : Q 
Values of 1 : C/ and 1 : as in formulas 4 and 7. 
No. 9. 1 : C_i = The probability that no member of any of the equivalent 
chromosome-pairs characteristic of the species (thus barring for the time 
being all consideration of the xx or xy chromosome-pairs) from the given 
ancestor will enter the Fi zygote. 
In such an occurrence the given ancestor and all of his or her lineal 
ancestors are entirely eliminated as contributors to the natural inherit- 
ance of the propositus, i. e., the Fi zygote, provided that such given 
