524 GENETICS IN RELATION TO AGRICULTURE 
The Inheritance of Defects.—By defects we refer specifically to 
abnormal structures or processes which are the almost invariable ex- 
pressions of particular genetic constitutions. Of these a vast number are 
known, particularly in man where in recent years a considerable amount 
of attention has been devoted to them. A very familiar example is 
hemophilia, a bodily condition such that the blood does not possess the 
ability to clot when blood-vessels are ruptured. The defect in man is 
determined by a sex-linked recessive factor and exhibits the same type of 
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Fia. 203.—Pedigree of a family of ‘‘ bleeders’ ne K. family, located in and about Car- 
roll Co., Maryland. The son, II, 2, was a bleeder but died without issue. The eldest son, 
III, 1, of the daughter, II, 3, was a bleeder from 18 up to 45 years, ‘‘often bled till he 
fainted.” He had 2 unaffected brothers and 3 normal sisters but 1 sister, III, 10, was a 
“‘bleeder until 40.’ He had a son, IV, 1, who was a very bad bleeder from 18 until toward 
middle life and a daughter, IV, 2, who often “‘ bled until she fainted’’ and eventually died of 
dysentery. All 19 children of the 2 normal brothers were normal and 9 children of the 
normal sister, III, 7. The affected sister, III, 10, had 3 sons and 2 daughters who were 
affected. IV, 5, is stated to be ‘‘a bleeder”’ and had by an unaffected husband 2 bleeding 
sons and 1 bleeding daughter besides 4 others who died of scarlatina. Her brother, IV, 8, 
had a daughter, V, 5, who was a bleeder until 15, and then died of a hemorrhage of the lungs 
consequent upon tuberculosis. There were other children all of whom died young of 
scarlatina. The normal brother, IV, 10, had 12 normal children. The next 2 had no 
offspring. The youngest son, IV, 14, began to bleed while an infant, grew worse until he 
was 25 and has since improved. He married a cousin who is also a bleeder and they have 
6 children. Three of the daughters have not bled as yet. V, 9, has been a bleeder since he 
was 8 months old and bleeds until he faints; V, 10, has been a bleeder since she was 8 
months old and V, 11, bleeds occasionally but not very severely. (After C. B. Davenport.) 
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inheritance as sex-linked factors do in the fruit fly. A family history 
showing the inheritance of hemophilia is outlined in Fig. 203. There 
is an analogous defect in the horse. In man a number of other defects 
have been traced some of which display a Mendelian type of behavior, 
and a surprisingly large number of them are sex-linked. 
Thus among dominant defects in man Guyer lists achondroplasy, 
abnormally short limbs along with normal head and body; keratosis, 
thickening of the epidermis; epidermolysis, excessive formation of 
blisters; hypotrichosis, a hairless and toothless ccndition; diabetes 
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