LINKAGE RELATIONS IN MENDELISM 105 
tution of the hereditary material and of the operation of the chromosome 
mechanism in the distribution of the hereditary units. 
Purple Aleurone and Waxy Endosperm in Maize.—A typical example 
of the relations which obtain for linked factors is given in the experiments 
which involve purple aleurone color and waxy endosperm inmaize. We 
have shown in Chapter V that aleurone color in maize in certain cases 
depends on a single factor difference, so that in J’, segregation is in the 
ratio 3 purple:1 white. For waxy endosperm, when contrasted with 
starchy endosperm, Collins has shown that starchiness is dominant and 
that in Fs segregation is in accordance with the normal monohybrid 
ratio, 3 starchy:1 waxy. The factors involved in these two cases are 
C for aleurone coloration and its recessive allelomorph e¢ for colorless 
aleurone, and W for starchy endosperm and its recessive allelomorph 
w for waxy endosperm. Collins found that when purple starchy corn, 
CCWW, is crossed with white waxy, ccww, F; is purple starchy, CeWw; 
but F'2 does not segregate in the expected dihybrid ratio 9 purple starchy: 
3 purple waxy :3 white starchy:1 white waxy. The data which he 
actually obtained from six ears are given in Table XIX. The calculated 
Taste XIX.—F, SEGREGATION OF Cross PuRPLE Starcuy & Wuite Waxy 
(After Collins) 
Becnumber | Nem’ | gums | bum | um | ay 
: Lae al A ce 
152 | 183 | 112 20 22 | 29 
301 | 579 372 62 63 | 82 
302 | 536 343 | 52 53 | 88 
303 627 409 57 62 99 
325 650 434 | 55 | 61 100 
380 161 104 17 18 22 
Observed totals. 2,736 1,774 263 279 420 
Calculated....... Oso 1,539 | 513 513 171 
Calculated 22.6 crossing-over. . ii 1,775 | 276 276 409 
ratio based on independent segregation evidently falls far short of agree- 
ment with the observed results, even though, when each pair of characters 
is considered separately, the agreement with the monohybrid ratio is 
very satisfactory. Thus for purple and white the observed totals are 
2037:699 giving a ratio of 2.98 :1.02, and for starchy and waxy the 
observed totals are 2053:683 giving a ratio of 3.00:1.00. The latter 
ratio is so close that it would be perfect if only one kernel were shifted 
from the starchy to the waxy class. Taking each pair separately, there- 
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