Humangenetik 14, 264--268 (1972) © by Springer-Verlag 1972

New Families, One with Two Recombinants for Estimation of Recombination

between the Deutan and Protan Loci

SERGIO AI~IAS and ALvAI~O RODI~iouEz

Laboratorio de Gen6tica Humana, Departamente de Mcdicina Experimental, Instituto Vene- zolano de Investigaciones Cientificas, Caracas, Venezuela

Received December 9, 1971

Summary. Using the simplified Edward's maximum likelihood method applied to 35 sons of 9 new families, one of which shows 2 recombinants, 1 normal and 1 compound hemizygotes from a population of German ancestry, an estimate of the recombination fraction between the protan and deutan loci has been attempted, including previous data from the literature.

The new 0 is 0.114 ~- 0.05 from the new data alone and 0.095 ~- 0.03 from the combined data, which are a little higher than former estimates based on families of smaller size. The distance between the deutan and protan loci might be, within its close proximity, farther apart than previously supposed.

Zusammen/assung. Es wurde die Rekombinationswahrscheinlichkeit zwischen dem Protan- and Deutan-Locus unter Einschlu$ yon eigenem Material sowie yon Familicnmateria] aus dcr Literatur neu gesch~tzt. Das eigene Material besteht aus 35 SShncn yon 9 Familien, von denen eine 2 Rekombinanten cnth~lt sowie 1 normale Person und 1 Compound-ttemizygoten. Die untersuchte Bev61kerung ist deutscher Abstammung. Es wurde die vereinfachte ,,maximum likelihood"-Methode yon Edwards verwendet. Das neue 0 ist 0,114 ± 0,05 auf Grund der neuen Daten allein and 0,095 ~: 0,03 auf Grund der kombinicrten Daten. Der Wert ist etwas h6her als frfihere Sch~tzungen auf Grund kleinerer Familien. Der Abstand zwischen dem Deutan- und dem Protan-Locus diirfte damit etwas gr6$er sein als frfiher angenommen.

Despi te the calculat ions of F rancesche t t i (1960), K a l m u s (1962, 1965), Pick- ford (1950) and others (Thuline et al., 1969) re la t ing to the expec ted f requency of compound hemizygotcs which should be found, ve ry few have ac tua l ly been localized (Pickford, 1950 ; Wal l s and Mathews, 1952 ; Siniscalco et al., 1964).

The deu t an and p r o t a n loci, recognized t o d a y as definite separa te genet ic ent i t ies have p roduced recombinants , b u t in ve ry low numbers ; so, p roper es t ima- t ions of 0 are scarce (Tanaka, 1964; Fraser , 1969); pedigrees wi th a ]urge number of sibs car ry ing alleles of different series, are rare. Only 2 families wi th as m a n y as 5 sons are known (Vanderdonck and Verriest , 1960; Thul ine et al., 1969). Besides, doub t s have been cast on the t y p e of genetic phenomenon t ak ing place in one of them, which showed 2 a p p a r e n t r eeombinan t s (Vunderdonck and Ver- riest , 1960), because of the ve ry low f requency of r ecombina t ion observed over so m a n y years of expec ta t ion (Thuline et al., 1969). I t is no t known whe ther this is due to a na tu r a l cause or to lack of ins ight in to the pheno typ ic peculiar i t ies .

This pape r deals wi th the e s t ima t ion of the r ecombina t ion f rac t ion of the deu t an and p ro t an loci f rom 9 kindreds , in which the mothe r ' s phase is known. One of the s tud ied families has 2 recombinan t s and is p resented in more detai l .

Estimation of Recombination between the Deutan and Protan Loci 265

1 2 i ® [ ]

01

III 19 18 35

2 15 1A

Fig. 1. Abridged pedigree for eolour vision showing two recombinants ( I I - -3 , I I ~ 4 ) with three types of sons. Horizontal bars: unidentified deutan gene; vertical bars: extreme prot- anomaly gene. Asterisc means an examined subject. Numbers below individuals state subject's age. I - -1 is in repulsion; I I I 5 is in coupling. The phase o f / - - 1 is known to have been

repulsion from evidences discussed elsewhere (Arias and Rodrlguez, 1971 a)

Ma te r i a l and Methods

l~eeently, in studying the distribution of colour vision genes among other traits, in an isolate of German ancestry which has been settled in this country for 128 years (Arias, 1971 ; Arias and Rodriguez, 1971 a, b ; Rodrlguez and Arias, 1971), we discovered in a large pedigree (Arias and Rodrlguez, 1971 a) several compound heterozygotes of t identical gene for extreme prot- anomaly and 3 different deutan genes, 2 of whom each have a recombinant son and 1 who has 2 recombinant sons. In 1 of these kindreds, the maternal grandfather is a compound hemizygote and a recombinant who transmitted his phase to his grandson; the phase in his mother was repulsion as argued elsewhere (Arias and Rodrlguez, 1971 a).

Furthermore, complete ascertainment was done for the families carrying the EPA gene (Rodrlguez and Arias, 1971), without any prior bias toward reeombinants (Arias and Rodrl- guez, 1971 a). The phase is known to be repulsion from overwhelming genealogical evidence, as discussed elsewhere (Arias and Rodriguez, 1971 a), in kindreds I, II , I I I , IV, V, VI, VI I I and IX. Kindred VII contains a mother with a known phase in coupling, and her son (IV-2 in Fig. 1). Kindreds VI I I and IX were discovered among the large pedigree mentioned above after that paper (Arias and Rodriguez, 1971 a) was completed and is also new information. There is still the possibility of finding frmn 1 to 5 more compound heterozygotes in repulsion among the sisters of the mother in kindred I X all of whom are carriers of deuteranopia.

We calculated ~? by the simplified methods for close linkage: Fraser's Estimates i and 2 and mainly Edward's method (Fraser, 1969; Edwards, 1971). All data on which the last known estimation was based (Fraser, 1969), were included, adding 5 more recomhinants: 1 (Pickford, 1950, 1962) not included as such (Thuline et al., 1969; Fraser, 1969) in a previous calculation (Fraser, 1969) and our own eases; also, 3 families without reeombinants recently published (Adam and :Fraser, 1970), have been included, but Waaler's (1969) family is not included because no certain identification of the phenotypes is available, as no anomaloscopic studies were performed.

Findings

4 o u t of' 35 sons ava i l ab l e for s t u d y f r o m t h e 9 k ind reds were r e c o m b i n a n t s .

T h e f a m i l y whose a b r i d g e d ped ig ree is i l l u s t r a t e d in F ig . 1 con ta ins 2 k ind reds

( IV a n d V I I ) a n d shows r e c o m b i n a t i o n in t h e second g e n e r a t i o n (11 - -3 a n d

1 1 - - 4 be ing t h e r e c o m b i n a n t s ) ; 1 1 - - 6 is p h e n o t y p i c a l l y no rma l , a n d has a t l eas t

266 S. Arias and A. Rodriguez :

Table 1. Estimations o /0 according to "simple" methods/or close linkage (Fraser; Edwards)

Included kindreds

Total Type of family No. of No. rocom- of b inants s o n s

Contributed information for each method

Ed- Fraser 1 Fraser 2

wards No. of non- No. of No. of non- No. of recom- recom- recom- recom- binants b inants b inants b inants

G6thlin c Brunner c Kondo I c Kondo I I c Vanderdonck and

Verriest Nemoto and

Murao d Pick ford Ichikawa c Jackson et al. d I Jackson et al. a I I Siniscalco et al. Thuline et al. Adam I Adam I I

4 pD pD Pd P d 0 + 9.143 0 0.666 0 3 pD Pd Pd 0 -t- 8.000 0 0.333 0 4 pD pD pD Pd 0 ~- 9.143 0 0.500 0 3 pD pD Pd 0 ~- 8.000 0 0.333 0

5 pD Pd Pd P D PD 2 + 4.000 2.67 0.100 0.20

3 pD pD Pd 0 -7 8.000 0 0.333 0 3 pD Pd pd 1 -7 8.000 4.00 0 0.17 4 pD pD Pd Pd 0 -7 9.143 0 0.666 0 3 pD P d Pd 0 ~ 8.000 0 0.333 0 3 pD P d Pd 0 ~- 8.000 0 0.333 0 3 pD P d pd 1 ~ 8.000 4.00 0 0.17 5 pD pD Pd Pd Pd 0 ~- 10.670 0 0.900 0 3 pD Pd Pd 0 ~ 8.000 0 0.333 0 3 pD Pd Pd 0 ~ 8.000 0 0.333 0

Sub-total 49 4 114.099 10.67 5.163 0.54

New data Arias et al. I 3 pD Pd Pd 0 & 8.000 0 0.333 0 Arias et al. l i b 4 P d P d P d P d 0 Jr Arias et al. I I I 4 pD Pd Pd Pd 0 -r 9.143 0 0.500 0 Arias et al. IV 3 PD pd pD 2 + Arias et al. V 5 pD Pd Pd P d pd 1 -7 9.143 2.286 0.300 0.15 Arias et al. VI 7 3pD 3Pd pd 1 -7 12.387 2.070 0.857 0.21 Arias et al. VII a 1 pd 0 -7 Arias et al. VII I 6 3Pd 3pD 0 -7 12.387 0 1.200 0 Arias et al. I X 2 P d pD 0 +

Sub-total 35 4 51.060 4.356 3.190 0.36

Grand-total 84 8 165.159 15.026 8.353 0.90

Es t imat ion From published cases From new data From combined data by each method

Edwards 4/49, 0 = 0.082 4/35, 0 = 0.114 8/84, 0 = 0.095 -7 0.0391 -7 0.0537 -7 0.032

Fraser 1 10.67/t24.769, 0 ~ 0.086 4.356/55.416, 0 = 0.079 15.026/180.185, 0 ~ 0.083

Fraser 2 0.54/5.703, 0 = 0.095 0.36/3.55, 0 ~ 0.101 0.9/9.253, 0 = 0.097

a Only family in coupling among the new data. b Mother in this kindred is a certain compound heterozygote al though she has only sons of one type. c Tanaka et al. (1964). d Thuline st al. (1969).

Estimation of Recombination between the Deutan and Protan Loci 267

1 normal X chromosome as she has 4 normal sons, only 1 of whom is illustrated ( 1 1 1 - - 7 ) . The detailed phenotypie description of the compound hemizygotes I I - - 4 and I V - - 2 and those in kindreds V and VI appears elsewhere (Arias and Rodrlguez, 1971 b).

Table 1 summarizes the data and the information for suitable families from this paper and from the literature.

The recombination fraction estimated from the published data combined with ours is 0.095 4- 0.032 using Edward's method; it is a little higher if estimated from our data only:0.114 4- 0.05.

Kindreds II , IV, VII and I X are unsuitable for the calculations in Fraser's methods; II , because only sons of 1 type are present, although the mother is a certain compound heterozygote; IV, because there are 2 recombinants and only 1 normal son; VI I and IX, because there are in both eases less than 3 sons.

Discussion

We obtained an estimation of 0 larger than the previous known one (Tanaka, 1964; Fraser, 1969). Our findings are not biased as the selection of the extreme protanomaly gene was complete and was not intended for linkage, being all suitable families included a posteriori in the estimation of the recombination fraction, with one exception discussed in Arias & Rodrlguez (1971a).

In the present ease the objection about the unfeasibility of combining sibships of 2 sons with larger ones (Fraser, 1969) is not valid because identification of all the phases is clear ; mothers in kindreds I, II, I I I and VI are sibs ; those in kindreds V and I X are also sibs. All kindreds contain the same protan gene whose path has been clearly established (Arias and Rodriguez, 1971a). l~ecombinants are easily identifiable among these kindreds in sibships of 2. The information available is sufficient to make probabilistic assumptions about phases unnecessary (Arias and Rodrlguez, 1971a).

Our kindred IV is the second instance of a family with 3 types of sons, 1 of whom is normal, on which 2 recombinants are claimed, but is the first in which a compound hemizygote and a normal occur together. Thuline et al. (1969) found it unusual that 2 recombinants occurred in a family, as certainly no other examples were known in 20 other families they had to study; since then 2 more (Adam and Fraser, t970) and from our data, 6 more families with 20 sons and no recombinants must be added to that group, as well as 2 kindreds with 12 sons and 1 recombinant in each.

Therefore, the occurrence of 2 recombinants in one family is a rare event, but not all too improbable, as it has happened twice in 32 families. I f the recombina- tion fraction is assumed to be O.1, and as the known 32 families with 98 sons including all of Thuline et al. (1969), Adam and Fraser (1970) and ours have a mean number of sons per family of 3.06, the probability for a three-son mother having 2 of them recombinants is 0.027 or about 3% and for a five-son mother, 0.072 or 7%, which are relatively low probabilities but well within the range of common expectation. No special explanations as the one suggested by Thuline et al. (1969) are thus necessary to account for the occurrence of such families.

268 S. Arias and A. Rodriguez: Recombination between the Deutan and Protan Loci

The obvious advantages for the es t imat ion of 0 in the present mater ia l are the larger families and the iden t i ty of the marker gene (extreme protanomaly) in all the kindreds. The informat ion available so far for the es t imat ion of the recombina- t ion fraction of the deu tan and pro tan loci has been increased by more t h a n 70%

with these new da ta which logically allow a bet ter es t imat ion to be made of 0 which might be a little larger t han was previously thought .

Very soon a m a x i m u m likelihood est imate is going to be calculated using the final da ta from the whole populat ion out of which the present informat ion was drawn.

References

Adam, A., Fraser, G. ]%. : The linkage between protan and deutan loci. Amer. J. hum. Genet. 22, 691--693 (1970).

Arias, S. : A note on the attempt to ascertain inbreeding through dermatoglyphics. Acta Genet. reed. (Roma) 14 (1971).

Arias, S., Rodriguez, A. : An informative large pedigree with four compound hemizygotes of three combinations of deutan and protan genes. (Submitted for publication, 1971a.)

Arias, S., l%odriguez, A. : Description of three different phenotypes for compound hemizygotes in various combinations of deutan genes with an identical gene of the protan locus. (Sub- mitted for publication, 1971b.)

Edwards, J. H. : The analysis of X-linkage. Ann. hum. Genet. 34, 229--250 (1971). Franceschetti, A. : Acquisitions r6eents couccrnant lea troubles cong6nitaux du sens chromatique

ct leurs relations avec lea aberrations chromosomiques. Arch. Klaus-Stift. Vererb.-Forseh. 85, 322--412 (1960).

Fraser, G. R. : Estimation of the recombination fraction between the protan and deutan loci. Amer. J. hum. Genet. 21, 593--599 (1969).

Kalmus, H. : Distance and sequence of the loci for protan and deutan defects and for glucose- 6-phosphate dehydrogenase deficiency. Nature (Lond.) 194, 215 (1962).

KMmus, H. : Diagnosis and genetics of defective colour vision. Oxford: Pergamon Press 1965. Pickford, R. W. : Three pedigrees for colour-blindness. Nature (Loud.) 16& 82 (1950). Pickford, 1~. W.: Compound hemizygotes for red-green colour vision defects. Vision Res. 2,

245--252 (1962). Rodrlguez, A., Arias, S. : Estimaci6n de la frecucncia de los genes de discromatopsia en un

aislado 6tnico con el uso de] anomaloscopio de Pickford-Nicolson. Acta cient, venez. 22 (1971).

Siniscalco, M., Fillipi, G., Latte, B. : Recombination between protan and deutan genes; data on their relative position in respect of the G6PD locus. Nature (Lond.) 204, 1062--1064 (1964).

Tanaka, K. : Recombination value between protan-type and deutan-type color-blindness loci. Jap. a. Genet. 89, 3 1 ~ 0 (1964).

Thuline, H. C., Hodgkin, W. E., Fraser, G. R., Motulsky, A. G. : Genetics of protan and deutan color-vision anomalies: an instructive family. Amer. J. hum. Genet. 21, 581--592 (1969).

Vanderdonck, R., Verriest, G. : Femme protanomMe et h6t6rozygote mixte. Biotypologie 21, 110--120 (1960).

WaMer, G. H. M. : Studies in colour vision. Avhand. Norske Vident. Acad. Oslo I. Nat.-Nat. Klas. Ny. Ser. No. 12, 6--9 (1969).

Walls, G. L., Mathews, R. W. : New means of studying color blindness and normal foveal color vision. Univ. Calif. Publ. Psycho]. 7, 1--172 (1952).

Dr. Sergio Arias Ing. Agr. Alvaro Rodrlguez I.V.I.C. Apartado 1827 Caracas, Venezuela