1. Y comb, 100 per cent. 2. Y comb, 50 per cent; I comb, 50 per cent. 3. Y comb, 50 per cent; oo comb, 50 per cent. 4. Y comb, 25 per cent; I comb, 25 per cent; oo comb, 25 per cent; absent, 25 per cent. Mating oo comb and Y comb should give the family types: 1. Y comb, 100 per cent. 2. Y comb, 50 per cent; oo comb, 50 per cent. 3. Y comb, 50 per cent; I comb, 50 per cent. 4. Y comb, 25 per cent; oo comb, 25 per cent; I comb, 25 per cent; no comb, 25 per cent. Finally, I comb and oo comb should give the following types of families: 1. Y comb, 100 per cent. 2. I comb, 100 per cent. 3. Y comb, 50 per cent; oo comb, 50 per cent. 4. I comb, 50 per cent; no comb, 50 per cent. Now, what do the facts say as to the relative value of these three hypotheses? Abundant statistics give a clear answer. In the first place, the progeny of two Y-combed F1 parents is found to show the following distribution of comb types: Y comb 471, or 47.3 per cent; I comb 289, or 29.0 per cent; oo comb 226, or 22.7 per cent; and no comb 10, or 1 per cent. The presence of no comb in F2 speaks for the second hypothesis, but instead of the 6.25 per cent combless expected on that hypothesis only 1 per cent appears. There is no close accord with expectation on the second hypothesis. Coming now to the F3 progeny of two Y-combed parents, we get the distribution of families shown in table 3. TABLE 3. +--------+-------------------------+---------------------------+ | Pen No.| Parents. | Comb in offspring. | | |-------------------------+------+-----+-----+--------| | | ♀ (F2) | ♂ (F2) | I | Y | oo | Absent.| |--------+-------------+-----------+------+-----+-----+--------+ | 707 | { 366 | 1378 | 18 | 16 | 9 | .... | | | { 522 | 1378 | 1 | 1 | 0 | .... | | | | | | | | | | | { 2250 | 2247 | 9 | 5 | 4 | 1 | | 763 | { 2700 | 2247 | 3 | 5 | 3 | 1 | | | { 3799 | 2247 | 5 | 4 | 3 | .... | | | | | | | | | | 769 | { 1305 | 911 | 7 | 4 | 6 | .... | | | { 2254 | 911 | 15 | 15 | 7 | .... | | |------+-----+-----+--------+ | Totals (142) | 58 | 50 | 32 | 2 | | Proportions (per cent) | 40.8 | 35.2| 22.5| 1.4 | | | | | ⎿⎵⎵⎵⏌ | | | | | 23.9 | +---------+-------------+----------+------+-----+--------------+