J . Zool., Lond. (1967) 152, 127-135

The genetics of the white tigers of Rewa

I A N W. B. THORNTON, K. K. YEUNG A N D K. S. SANKHALA * Department of Zoology, University of Hong Kong

(Accepted 13 December 1966)

(With 1 colour plate and 3 figures in the text)

An up-to-date pedigree is provided for the white tigers of Rewa, and it is pointed out that the hypothesis that the characteristics “white” are determined by an autosomal recessive gene “w”, is consistent with the known pedigree. Suggestions are made regarding future crosses.

Contents Page

. . . . . . . . . . . . 1 2 1 Introduction . . . . . . .. . . The pedigree . . . . . . . . . . . . . . . . . . . . . . 128 Genetics . . . . . . . . . . . . . . . . . . . . . . 1 3 0 Suggested future crosses . . . . . . . . . . . . . . . . . . 135 References . . . . . . . . . . . . . . .. . . . . . . 135

Introduction

The only case of true albino tigers which has been recorded was in the old princely state of India, Cooch Behar, in 1922, when two young tigers were shot which were white, with pink eyes.

Tigers of varying shades of off-white and cream, with dark grey or chocolate coloured stripes, are known from Assam, Bengal and Bihar, but the most well-known “white” tigers are those from the old princely state of Rewa, which is now part of Madhya Pradesh. Nine such tigers have been seen in this area in the last 50 years, the most recent one, which proved also to become the most important, in 1951. In May of that year, a tigress with a litter of four nine-month old cubs was flushed from cover; one of the cubs, a male was “white”. This cub was kept under observation and later captured. It was named Mohan and kept by the Maharaja of Rewa with a normally-coloured tigress which had also been captured in the district, and which was named Begum. The union proved productive, and from it a line of tigers has been bred which has to date resulted in a further 26 “white” tigers, some of which have been sent from India to zoos in other parts of the world.

The “white” tigers of Rewa have ashy grey-brown stripes on an off-white background, ice-blue eyes, pink noses and pink paw pads. Pigmentation is thus reduced, but not com- pletely lacking as in true albinos (Plate I(a) and (b)). These tigers are not deaf, as are homozygous white cats (Searle, 1959); Mohan, Rani and Raja (Fig. 1) are known to re- spond when called by name. Some measurements taken in Delhi (Table I) suggest that they are larger than normal tigers not of the Rewa line. Though they are not completely

* Delhi Zoological Park, New Delhi. 127

128 I A N W . B. T H O R N T O N , K . K . Y E U N G A N D K . S . S A N K H A L A

white, this word will be used adjectivally from now on without quotation marks, for convenience. Accounts of the white tigers of Rewa have been made by Gee (1964a,b) and Roth (1964), but a full pedigree and a discussion of the genetics has not yet been provided.

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TIC, 1. Pedigree of the Reaa tigers Solid symbols indicate >ellow tigers, plain symbols whte tigers. Dotted connections indicate matings not le t productne. Lnderlining indicates death; dates are provided where known. Litters are not airaiiged chronologically, but for convenience. Abbre\iations used for locations of tigers: AZ, Ahmedabad Zoo, BZG, Bristol Zoological Gardens ; CZG, Calcutta Zoological Gardens; DZP, Delhi Zoological Park; GP, Gokindgar11 Palace, Keua; NZPW, National Zoological Park, Washington; PMDC, sold to P. M. Das, Calcutta; VGB, Victoria Garden, Bombay; US, to be taken to America by Ralph S. Scott.

The nediorw r---a- -- - _-- We have obtained information from institutions owning descendants of the original

In all, eight crosses involving the Rewa line of tigers have resulted in the production of mating of Mohan, and an up-to-date pedigree is shown in Fig. 1.

PLATF I (a). The three white cubs of Rani’s third litter. (b) Raja (standing) and Radha, courting.

[To face page 128

T H E G E N E T I C S O F T H E W H I T E T I G E R S O F R E W A 129

offspring. The original Begum-Mohan cross produced three litters between 1953 and 1956, all ten cubs of these litters being normal in colour, like their wild-caught mother. The second series of litters was the result of matings between Mohan and his yellow daughter Radha. White cubs were produced in each of these four litters, one normally-coloured female cub, Malini, occurring in the second of these, and a normal male, Ramesh, and a normal female, Ratna, in the fourth. The third series of matings, like the second, was a backcross, this time between Sultan and his mother Begum: four litters were produced consisting of

TABLE I

Cornparisom in height and weight between Rewa white tigers and yeflow tigers not of the Rewa line

Name

Arjun Raja Ashrafi Rani Gita Litter shown on Plate I Litter shown on Plate I Litter shown on Plate I

Phenotype Sex

yellow male white male yellow female white female yellow female white female white male white male

Age * years months

9 9 7 9 9 9 7 9

10.5 7.5 7-5 7.5

Shoulder height * Weight* ft in (kg)

3 0 - 3 6 - 2 8 - 3 3 - 2 1 31 2 0 35 2 1 40 1 11 35

~~~ ~~

* On 2. VIII. 66.

12 cubs in all, all of which were yellow. Mohan was then kept with Sukeshi, a white tigress of the first litter of the Radha-Mohan cross, and produced three litters; all six cubs of these litters were white. The fifth cross was between Sukeshi’s white sister Mohini, and Samson, Radha’s yellow brother and the son of Mohan and Begum, the wild-caught normally coloured tigress. Two litters have so far resulted; the first consisted of one white and one yellow male cub, and a yellow female; the second consisted of two yellow females. Roth (1964) describes the female in the first of these litters as “normal” in the text, but designates it as “light yellow” in the accompanying diagram. However, we are informed by the authorities of the National Zoological Park, Washington, that the female in question has been of normal coloration since birth. Rani and Raja, white siblings o,ut of Sukeshi, were mated in Delhi, and produced three litters, all seven of the resulting cubs being white. The seventh cross was between the normally-coloured tigress Malini and the white male Neeladri, siblings of the second litter of the Radha-Mohan cross; two cubs were born, a white female and a normally-coloured male. The latest successful mating was between Vindhya, a yellow female of the third litter of the Begum-Mohan cross, and a male (Suraj) of unknown origin; two yellow males and a yellow female were born.

Several deaths are recorded in the pedigree. In the F1 generation, one female of the third litter of the Begum-Mohan cross died as an infant, and another, Narbada, died of wounds received in a fight with a presumptive mate whom she killed. In the next generation, two white cubs of the third litter of the Radha-Mohan cross died as infants, and Ramu, a white male of the fourth litter, died following pneumonia when he was 21 months old; the

1-30 I A N W . B . T H O R N T O N , K . K . Y E U N G A N D K . S . S A N K H A L A

yellow female of the Vindhya-Suraj cross died as an infant. Of the offspring of Raja and Rani, Rukko. a white female of the first litter, died after being mauled by her mother; her brother Krishna, who was also mauled, survived; both white cubs of Rani’s next litter died within a day due to her careless handling and neglect. Sukeshi discarded the two white cubs of her first litter and both died within three days. At Washington, two of the offspring of Mohini‘s first litter died at the age of about 19 months of feline enteritis, and one female of her second litter was stillborn; recently, Samson died of kidney malfunction.

Abandonment and maltreatment of a first litter is not unusual in tigers; early deaths which are unexplained cannot be ascribed to genetical causes, although it is interesting to note that a11 yellow males of this pedigree have survived, except Samson which died at the relatively advanced age of 11 years.

Genetics

A doubt raised as to the discontinuous nature of the character “white” has now been dispelled. If it is assumed that the tiger is a diploid animal producing haploid gametes as in other feline species such as the domestic cat, the inheritance of the character “white” in the knoun pedigree of white tigers of Mohan‘s lineage can be explained by the following hypothesis.

The character “white“ is determined by a single autosomal recessive gene which we now designate 11 ; its dominant allele determining the normal colouring of eyes, coat, nose and pads (yellow. for short) would thus be designated W. According to this hypothesis, all white tigers must be of the genotype ww and yellow tigers either Ww or WW.

It follows that crosses between two yellow tigers can yield either yellow cubs only, when one or both parents are homozygous, or both yellow cubs and white cubs in the theoretical ratio of 3 : 1 uhen both parents are heterozygous. Crosses between two white tigers can yield only white progenj, whereas crosses between a white tiger and a yellow tiger can yield two types of progeny depending on the genotype of the yellow parent. If the yellow parent is U’U’, then all the progeny must be yellow, but if the yellow parent is Ww, then the progeny may consist of both yellow cubs and white cubs and the more offspring that are produced the greater will be the chances that the ratio of yellow to white offspring will approach 1 : 1. It also fellows that all yellow tigers out of a white parent must be of the genotype W H .

HOM can this hypothesis explain the known pedigree? The cross between Mohan and Begum produced ten cubs, all yellow, in marked contrast

with the cross between Mohan and his yellow daughter Radha which produced both yellow cub\ and white cubs, and thereby shoned segregation of the characters “white” and “yellow” in the bachcross generation. Of the remainder of the crosses successful in the production of progeny up to now, crosses between two white tigers have produced nothing but ahite cubs. and crosses between a white tiger and a yellow tiger out of one white parent have all produced both yellow cubs and white cubs (Table 11). No white cub has been produced in crosses between two yellow tigers, i.e. Begum by her son Sultan, and Vindhya by Suraj (not in the Rewa line). Although Sultan and Vindhya are, on the hypothesis, heterozygotes. all 15 cubs resulting from these crosses were yellow. These facts demonstrate that genes determine the pair of contrasting characters “white” and “yellow”, and that “white” js recessive to “yellow”.

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Figure 1 shows no evident pattern of criss-cross inheritance, nor is the white phenotype limited to one sex. Thus if sex-determination in the tiger is chromosomal, as in domestic cats (XX. X Y type), then it can be said that the recessive gene 11’ is not sex-linked, but is autosomal as assumed on the hypothesis.

It is most unlikely that a mutation in the germ-cells of Mohan’s parents was responsible for the appearance of the white characteristics of Mohan. It is highly improbable that such a mutation would occur in both parents, as would have to have been the case if “white” were recessive. and if it occurred in only one parent “white” would have to be dominant to show in Mohan. The offspring of Mohan’s first series of matings, however, were all yellow (Fig. 1). rendering the latter supposition highly unlikely. Moreover, the offspring of Mohan’s second series of matings, to Radha, would be identical genotypically with those of the first series if “white” were dominant (both would be between a heterozygous male and a homozygous female). The progeny resulting from these two series, however, are markedly different, showing segregation in the second series but not in the first. The facts that white tigers had been seen in the Rewa area for some decades before 1951, and that one was shot only four years before Mohan’s birth. also suggest that the mutant “white” did not arise with Mohan.

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FIG. 3. Possible genotypes of the forest family. Symbols as Fig. 1.

The father of Mohan was not seen, but his mother was (the possibility that this tigress was a foster-mother is ignored for the purpose of this argument), as were Mohan’s three litter-mates; only Mohan of these five tigers was remarkable in being white, and it may be assumed that the others were yellow. On the hypothesis, Mohan’s mother must have been heterozygous (were she homozygous yellow no white cub could have been in her litter, and as we have seen. the possibility that Mohan was a mutation is extremely unlikely); Mohan’s father could have been either heterozygous yellow or homozygous recessive white, since he must have contributed a “white” gene. The possible genotypes of this forest family are shown in Fig. 3.

Begum is probably hcmozygous yellow (Fig. 2); were she heterozygous it is highly probable that there would have been at least one white cub out of the ten produced when she mas crossed to Mohan (Table 11). The results of the Begum-Sultan matings at Ahmedabad gi\e support to the view that Begum is homozygous; on the hypothesis Sultan is heterozygous whatever the genotype of Begum may be, thus if Begum were also heterozygous some white cubs might have been expected in the resulting litters; how- ever, all 12 cubs produced were yellow (Table 11).

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Ratna is now being introduced to Krishna at Delhi; Ratna is a presumed heterozygote, so approximately equal numbers of white and yellow cubs may be expected from resulting litters. At Bristol, Champa and Chameli are being kept together; if successful, this cross should result in only white cubs. Attempts are being made at Delhi to mate Raja to Radha; both white cubs and yellow cubs may be expected among the progeny.

Apparent ditficulties requiring reconciliation in our hypothesis may be noted from an examination of the results of the crosses recorded in Table 11. Although there is no signifi- cant deviation from expectation at the 5 :< probability level in any of the crosses, the pro- portion of jellow cubs in cross 5 is high (four out of five) in contrast to that of cross 2

Phenotypes of offspring Obsen ed Expected

Cross yellow white yellobv white Total offspring Chi-square Probability

* Parents of Mohan 3 1 2 2 4 Radha x Mohan 3 11 7 7 14 Mohini :i Saiiison 4 1 2.5 2.5 5 Malini x Keeladri 1 1 1 1 2

13 10.5 10.5 21 0.76 0’30-0.50 Total 8

* Total including parents of Mohan 11 14 12.5 12.5 25 0.16 0.50-0.70

* Chi-square calculated using Yates’s correction for small numbers.

(three out of 14). However, these results are not incompatible with our hypothesis; in fact they give support to our contention that “white” is determined by a single locus. Suppose we consider two independent loci each duplicating the effect of the other, and invoke such a hypothesis to explain the high proportion of white cubs in cross 2, we cannot then account for the high proportion of yellow cubs i n cross 5 without lowering the level of statistical significance. If we consider two loci not duplicating each other’s effect, for example, two complementary loci jointly responsible for the production of the yellow phenotype, we are then led to the conclusion that the white phenotype is not necessarily homozygous, for which. up to now, we have evidence to the contrary. The only difference between cross 2 arid cross 5 is that one in\.olves a white male while in the other it is the female that is white. It might be supposed that the mechanism of transmission of gametes carrying genes w or M’. f rom heterozygotes is related to the parental phenotypes, including their sex, thus producing a real difference in the proportions of phenotypes in the progeny of the two crosjes. There is no evidence in support of this. however, in the pedigree before us.

If all crosses presumably between genotypes TV\t- and wi’ are pooled (Table 111) then the probability that the observed deviation from the expected proportions of phenotypes in the otfspring is a chance deviation is very high ( P = 0.30 to 0.50), and if the original forest mating is regarded as being between these genotypes (Fig. 3 (a)), still higher ( P = 0.50 to 0.70).

T H E G E N E T I C S O F T H E W H I T E T I G E R S O F REWA 135

In the absence of evidence to the contrary, we thus suggest that the discrepancies observed be considered as chance deviations.

Suggested future crosses

The hypothesis proposed here is simple, and capable of explaining the observed facts. Since it rests on the premise that the character “white” is strictly gene determined and that white tigers must be genetically pure, it is also capable of being tested. Hitherto, all white tigers in the Rewa pedigree have been bred out of at least one white parent; the possibility that non-genic factors are involved in the production of the white phenotype, however unlikely on the existing evidence, cannot, therefore, be totally excluded. However, crosses between presumed heterozygous yellow tigers would, if any white cubs resulted, exclude this possibility. This has not yet been done. Crosses which would serve this purpose and which appear to be practicable are those between Malini and her son in Calcutta, and between Kesari and Ramana in Washington. If the possibility of the operation of non- genic factors were finally excluded by the occurrence of any white cubs in the progeny of any of these crosses, breeders would be able to make crosses with complete confidence.

It would also be advisable at this stage in the lineage to cross white tigers of the Rewa line with yellow tigers outside this line in order to safeguard against inbreeding depression. Such matings might also confirm our view that no factor for the production of the white phenotype was present in Begum, the yellow tigress first mated to Mohan.

We wish to thank H.H. the Maharaja of Rewa, Mr Hari Singh, and the authorities of the Calcutta, Washington, Ahmedabad and Bristol zoos for providing information on tigers in their care.

REFERENCES

Gee, E. P. (1964a). The wifd life of India. London: Collins. Gee, E. P. (19646). The white tigers. Animals 3 (11): 282-286. Roth, W. T. (1964). The rare white tigers of Rewa. J. Cat Genet. 1 ( 3 ) : 18-19. Searle, A. G . (1959). A study of variation in Singapore cats. J. Genet. 56: 1-16.