Inheritance of Characteristics in Domestic Fowl

CHAPTER XI.

Chapter 182,004 wordsPublic domain

INHERITANCE OF BLUE COLOR, SPANGLING, AND BARRING.

A. BLUE COLOR.

Color-patterns are generalized, like the barring, spangling, and "blueing"; or localized, like the wing-bar or hackle and saddle lacing. We have to consider at present the method of inheritance of the former of these kinds of color patterns. As is well known (Bateson, Saunders, and Punnett, 1902, 1903), the Blue or Andalusian fowl is a heterozygote and, as such, produces white gametes and also black gametes.[10] The "blue" is, indeed, a fine mosaic of white and black. The barbules of a blue feather are seen to be finely barred with alternating pigmented and unpigmented zones. The pigment consists of the ordinary melanic granules of a dark sepia color.

[10] Wright (1902, p. 401) recognizes the variability of the blues. He advises the breeder of Andalusians that: "Black and white ones [offspring] can be weeded out at once; two or three months later birds absolutely too light, or dark and smoky, can be selected."

My original blues arose (in pen 502) from a White Leghorn hen B (recognized as heterozygous but of unknown origin), mated to a black Minorca. These blues are referred to in my 1906 report. They were both females and were mated (in pen 636) to a white cock (No. 340) similarly derived. Of 49 offspring, 11, or over 22 per cent, were black and 78 per cent either pure white (35 per cent of all), white with black specks (22.5 per cent) or white-and-black mosaic, _i. e._, blue (20.4 per cent), but the latter were very variable in the quality of the blue. Let us designate the whitening factor of the White Leghorn by _W_ (its absence _w_, resulting in black) and the blueing by _M_ (its absence by _m_). Then, assuming that the blue females produce germ-cells _MW_, _Mw_, _mW_, _mw_, in equal numbers, and that the white male produces the same, we may expect in 16 F2 offspring the combinations shown in table 64.

TABLE 64.--_Combinations in zygotes of the second hybrid generation of the blue strain._

The relation between the calculated and the actual percentages is as follows:

White + black specks in females: calculated, 62.5; actual, 57.5. Black: calculated, 25; actual, 22.1. Blue: calculated, 12.5; actual, 20.4.

That the agreement is not closer must be attributed to the fact of small numbers and the premature death of many of the chicks, in consequence of which their adult plumage colors were not fully revealed. Also, many "blue" chicks produce white adults with black specks in the plumage.

It is to be observed that this explanation calls for a special mosaic (blueing) factor, but this mosaic factor brings about a blue plumage only when the "white" factor is diluted, _i. e._, heterozygous.

In the next generation (pen 733) I mated 2 blues together. This mating is generally regarded as a unifactorial one (producing gametes _WM_, _wM_) and to give in every 4 offspring 1 black, 2 blue, and 1 white. I obtained the expected 50 per cent of blues, but always an excess of blacks and a deficiency of whites (49:35:16, respectively). This result is doubtless due to the accident that a large proportion of the chicks were described young, for it appears from my records that some blues become white when older and some "blacks" are certainly _blue-blacks_. The deficiency of whites becomes an _excess_ of whites in the adult stage. The whites obtained from the blues are usually, but not always, splashed with black spots.

B. SPANGLING.

As is well known, hybrids between black fowl and White Leghorns are usually white with black patches in the females, while their brothers are mostly entirely white. This "spangled" condition is a heterozygous one just as truly as the "blue" condition is. When a splashed hen is mated to her white brother a certain proportion of the offspring are splashed again, _i. e._, one-half of 50 per cent or 25 per cent, that being the proportion of heterozygous females. Actually in 150 offspring 19.4 per cent were splashed and 18.6 per cent black, while 62 per cent were recorded (largely from unhatched chicks) as pure white. The splashing reappears in about the expected proportion of cases. In my pen 633 I take the spangled females to form gametes _WS_, _Ws_, _wS_, _ws_, while the male seems to form gametes _Ws_, _ws_; _S_ being the spangling factor. Then [♀ _WS_, _Ws_, _wS_, _ws_] × [♂ _Ws_, _ws_] gives the combinations shown in table 65.

TABLE 65.--_Combinations in zygotes of the second hybrid generation of the spangled strain._

This analysis indicates that we should occasionally see a spangled male, and this expectation is realized. Thus No. 1250 ♂ is an F2 out of White Leghorn A and the Rose-Combed Black Minorca No. 9. He is white with black spots covering about 10 per cent of the plumage, and No. 4222 ♂ of similar origin has much black on his chiefly white plumage. When they are mated to spangled hens of similar origin with themselves (pen 775), whites, blacks, and spotted, spangled, and blues occur in the proportions of 1, 17, and 12, respectively. Here again there is a deficiency of whites in the birds as described, a deficiency again probably due to immaturity.

Of the mottled condition all degrees are found, from white splashed with black to black with white spots; also, blue is very common in the offspring of two mottled birds. The relation of these patterns is very complex and much time would be required for their complete analysis, but it seems certain that there is a spangling or mottling factor, but that, as in canaries, guinea-pigs, and rats, the precise pattern is not inherited. There are, to be sure, in poultry, so called _races_ of spangled birds with well-defined patterns, such as the spangled Polish, spangled Hamburgs, and so forth, but it is the experience of breeders that they do not reproduce their patterns closely. The prize-winning birds--those which conform to the breeder's ideals--are only a small proportion of each family of offspring. For instance, the Ancona type of plumage, which is black, each feather tipped with white, has to be carefully sought for in the progeny of each Ancona pen. The same is true of the Silver Spangled and Golden Spangled Hamburgs. There is little true spangling in the first plumage; the darker chicks prove the best; that is, there is the same tendency to grow whiter with age that I have noted above. And, finally, only a few birds in any flock are even fairly good show birds.

C. BARRING.

The presence of bands of black running at intervals across the otherwise white feather is a condition found in many types of poultry as well as various wild birds. It has become a fixed character in the Barred Plymouth Rock, which derived it in turn from the barred Dominique, whose barring was probably derived from the Cuckoo birds of England. Barring is also said to result from some crosses between white and black birds.

In my breedings barred birds have arisen several times:

(1) _White Cochin × Tosa._--This case was referred to in my earlier report.[11] In the first generation of hybrids all males were barred. In the second hybrid generation I got 15 chicks that were white or nearly so, 25 with the Game color, and 16 barred. Remembering that only the males are barred and that the young heterozygous females are classed with Games, it appears that the barring is a heterozygous condition, occurring actually or potentially in about 50 per cent of the second hybrid generation and that, the whites and some of the Games are extracted types. This conclusion is confirmed by further breeding. In pen 663 I bred 2 extracted white hens of Cochin-Tosa origin to a white cock and got 12 chicks, of which all were white, except that 3 showed a trace of reddish color. From the extracted Games bred together I got 36 chicks, all Games. In the case of this cross, consequently, barring is clearly heterozygous and confined to the male sex.[12]

[11]: 1906, page 49, figs. 35, 37, 37a.

[12] Goodale, 1909, has shown that in Plymouth Rocks males may be and females usually are heterozygous in barring. There is thus a clear difference between the barring of the Cochin × Tosa hybrid and that of the Plymouth Rock. The question of the heterozygous nature of the female sex, fully discussed by Goodale, will be considered by me in another place. [Note at time of correcting proof.]

(2) _White Leghorn Bantam × Dark Brahma._--This cross was referred to in my report of 1906. From the table given there it appears that I got 5 barred fowl in F1 out of a total of 51. In pen 701 I attempted to see if I could fix this barring. I used the best barred cock of the F2 generation and the best barred hens of F1 or F2. The result was as shown in table 66.

TABLE 66.--_Distribution of color in F2 or F2 hybrids of the barred strain._

[ABBREVIATIONS: W.L. = White Leghorn; Dk.Br. = Dark Brahma.]

+---------------------------------------+---------------------------------+----------------------------+ | Mother. | Father. | Offspring. | +------+----+-------------+-------------+------+----+-------------+-------+------+------+------+-------+ | | | | | | | | | | | Dark | | | No. |Gen.| Races. | Color. | No. |Gen.| Races. |Color. |White.|Black.| Brah.|Barred.| | | | | | | | | | | | | | +------+----+-------------+-------------+------+----+-------------+-------+------+------+------+-------+ | | | | | | | | | | | | | | 721 | F1 |W.L. × Dk.Br.|Dark barred | 1898 | F2 |W.L. × Dk.Br.|Barred.| .... | 5 | 7 | 5 | | 894 | F2 | Do. |Well barred | 1898 | F2 | Do. | Do. | .... | 9 | 3 | [A]10 | | 965 | F2 | Do. |Medium barred| 1898 | F2 | Do. | Do. | 2 | 16 | 4 | 8 | | 1335 | F2 | Do. |Dark barred | 1898 | F2 | Do. | Do. | 1 | 14 | 1 | 2 | | 1772 | F2 | Do. |Poorly barred| 1898 | F2 | Do. | Do. | .... | 4 | 7 | [B]5 | | 1915 | F2 | Do. |Fairly barred| 1898 | F2 | Do. | Do. | .... | 10 | 4 | 5 | | 2576 | F2 | Do. | Do. | 1898 | F2 | Do. | Do. | .... | 9 | 11 | 3 | | | | +------+------+------+-------+ | | | Totals (145) | 3 | 67 | 37 | 38 | | | | Percentages | 2.1 | 46.2 | 25.5 | 26.2 | +------+----+-------------------------------------------------------------+------+------+------+-------+ [A] Including 1 blue. [B] Including 2 blue.

This result suggests the interpretation that one of the parents, probably the male, contains both heterozygous black and barring, while the other parent lacks the supermelanic coat and has homozygous barring. Then of the offspring half will be barred and half will be black and, consequently (since only the non-black show their barring), one-fourth will appear barred, one-fourth will appear of the Dark Brahma type, and half will be pure black or have the pattern obscured by the supermelanic coat.

(3) _White Leghorn Bantam × Black Cochin._--In still another experiment (pen 511) I crossed a White Leghorn bantam and a Black Cochin as described in my report of 1906. Of 24 hybrids that developed, 10 were white or nearly so, 7 were black, and 7 were barred black and white. The White Leghorn was heterozygous in white (half of the offspring being not white) and heterozygous to barring. In pen 650 the barred birds were mated together with results as given in table 67.

On the assumption that the zygotic formula of both hens and cocks is _BbN2Ww_ (compatible with a barred plumage) we get four-sixteenths of the offspring white, three-sixteenths mottled or barred and nine-sixteenths black or Game, thus approximating the observed result; i.e., 21, 16, 47 as compared with 23, 21, 40. The result supports the hypothesis of a barring factor, B.

TABLE 67.--_Distribution of color in offspring of barred White Leghorn × Black Cochin hybrids._

+--------------------------------------+--------------------------------------+-------------------+ | Mother. | Father. | Offspring. | +---+----+---------------------+-------+---+----+---------------------+-------+---+---------+-----+ |No.|Gen.| Races. |Color. |No.|Gen.| Races. |Color. |Wh.|Spangled,|Black| | | | | | | | | | | barred | or | | | | | | | | | | |and blue.|Game.| +---+----+---------------------+-------+---+----+---------------------+-------+---+---------+-----+ |263| F1 |Bl. Coch. × Wh. Legh.|Barred.|265| F2 |Bl. Coch. × Wh. Legh.|Barred.| 8 | 8 | 16 | |361| F1 | Do. | Do. |265| F2 | Do. | Do. | 7 | 4 | 15 | |364| F1 | Do. | Do. |265| F2 | Do. | Do. | 8 | 9 | 9 | | +---+---------+-----+ | Total. |23 | 21 | 40 | +-----------------------------------------------------------------------------+---+---------+-----+