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Piebald rats and selection

Chapter 71: Table 53.—Classification of the descendants through three generations of the two original mutants, ♂ 4763, +5½, and ♀ 5153, +5¾. The parents are in every case of grade 5½ or 5¾.
By William E. Castle
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About This Book

Investigators present a controlled breeding study that tests whether Mendelian determiners remain unchanged during crosses by selecting for increased or decreased pigmentation in piebald coat patterns of laboratory rats. They describe methods for grading dorsal pigmentation, establish parallel plus and minus selection lines, perform return and hybrid crosses with different stocks, and tabulate multigenerational outcomes. Statistical summaries and plates illustrate shifts in pigment distribution and the response to selection. The results are analyzed with respect to the theory of pure gametes and genotype–phenotype distinctions, showing that extracted recessive patterns and selection responses complicate simple notions of gametic purity.

Table 52.—F₁ offspring of the original mutant male, 4763, +5½, mated with females of the minus series.

Grade of mother. Grade of offspring, lower group. Grade of offspring, upper group.
-1 ¾ ½ ¼ 0 +¼ +½ +¾ +1 +1¼ +1½ +1¾ +2¼ Totals. Means. Standard deviation. +4 +4¼ +4½ +4¾ +5 Totals. Means. Standard deviation.
-2 1 1 1 3 1 2 1 1 1 1 13 +.40 2 5 3 2 12 4.46
-2¼ 1 1 1 2 2 2 3 1 1 14 +.70 2 4 3 9 4.53
-2½ 2 1 1 4 +.31 2 3 1 6 4.21
-2¾ 1 1 2 4 +.18 2 1 1 4 4.19
Totals or means 2 1 1 2 7 3 5 4 2 3 2 2 1 35 +.49 .77 6 11 6 6 2 31 4.43 .31

Table 53.—Classification of the descendants through three generations of the two original mutants, ♂ 4763, +5½, and ♀ 5153, +5¾. The parents are in every case of grade 5½ or 5¾.

Generation. Grade of offspring.
Lower group. Upper group.
3¼ 3½ 3¾ 4 Totals. Means. Standard deviation. 5 5¼ 5½ 5¾ Totals. Means. Standard deviation.
F₁ 3 3 6 3.87 6 4 10 5.60
F₂ 1 1 2 3.37 2 3 15 10 30 5.52
F₃ 1 7 3 11 5.55
Totals or means 1 1 3 3 8 3.75 .25 2 4 28 17 51 5.54 .19

Table 54.—F₂ descendants of the original mutant male, 4763, +5½, mated with females of the plus series. (Compare Table 51.)

Grade of (F₁) parents. Grade of (F₂) offspring.
Lower group. Upper group.
3 3¼ 3½ 3¾ 4 4¼ 4½ Totals. Means. Standard deviation. 5 5¼ 5½ 5¾ Totals. Means. Standard deviation.
Lower group parents 3⅝ 2 1 10 8 1 22 3.56
3¾ 1 2 2 7 2 1 15 3.92
3⅞ 1 2 6 8 4 1 22 3.92
Totals or means 2 3 14 16 16 6 2 59 3.78 .33
Upper group parents 5¼ 1 1 3.50 2 2 5.50
5⅜ 1 1 3 1 4 10 3.90 2 6 49 13 70 5.51
5⅝ 2 5 7 5.43
Totals or means 1 2 3 1 4 11 3.86 .35 2 8 56 13 79 5.50 .15

Table 55.—F₂ descendants of the original mutant male, 4763, +5½, mated with females of the minus series. (Compare Table 52.)

Grade of F₁ parents. Grade of (F₂) offspring, lower group parents. Totals. Means. Standard deviation.
-2 -1¾ -1 ¾ ½ ¼ 0 +¼ +½ +¾ 1 1¼ 1½ 1¾ 2 2¼ 2½ 3¼
¾ 1 1 1 3 .58
⅝ 1 1 1 3 1 1 2 1 11 .57
⅛ 1 1 1 1 1 2 1 1 9 .80
0 1 3 3 3 1 4 1 1 3 2 22 .72
+¼ 1 1 1 3 1.00
+½ 1 1 1 1 4 -.12
+1 1 1 1 1 1 1 2 1 9 .19
Totals or means 2 1 4 1 6 4 9 1 2 2 9 4 4 2 5 1 3 1 61 .58 1.17
Grade of F₁ parents. Grade of (F₂) offspring, upper group parents. Totals. Means. Standard deviation.
-2 -1¾ -1 ¾ ½ ¼ 0 +¼ ½ ¾ 1 1¼ 1½ 1¾ 2 3½ 4 4¼ 4½ 4¾ 5 5¼ 5½ L[1] U[2] L[1] U[2] L[1] U[2]
4⅛ 1 2 1 1 1 1 1 3 5 4.85
4¼ 1 1 6 1 1 1 1 10 4.62
4⅜ 1 1 2 1 1 2 4 4.56
4½ 1 2 2 1 1 2 4 10 6 8 4 6 6 41 4.78
4⅝ 1 1 1 1 1 2 3 2 8 4.91
Totals or means 1 1 2 4 2 1 3 1 2 9 18 10 12 9 7 14 68 +.75 4.77 1.03 .44

[1] Lower group offspring, -1¾ to +2 inclusive.

[2] Upper group offspring, +3½ to +5½ inclusive.