Section 14 — Animal Genetics and Breeding 



In 1956, Strong and Hardy reported on a new 

 luxoid condition in mice. It arose in a mouse 

 of the F5 after crossing a polydactylous mutant 

 of the Brpb subline, of the NHO/St strain, to 

 C57/St. (This condition has been designated 

 first.) The condition, according to Strong and 

 Hardy, was similar, but differed in some respects, 

 from previously reported luxoids. In 1962, 

 Forsthoefel reported that there were, in fact, 

 differences between Strong's luxoid and those 

 reported by Carter and by Green. 



The present communication will introduce a 

 concept of parity and its effects on the segrega- 

 tion of genetic traits. Mice were bred through- 

 out their reproductive life with some having as 

 many as thirteen litters. Points were plotted 

 for each parity for these traits: percent having 

 normal feet, percent having either poly on one 

 hind foot (Poly 1) or on both hind feet (Poly 2), 

 percent having some form of luxoid, and percent 

 of total defective mice. It was learned that the 

 percentage of animals having some defect did 

 not change with increased parity. However, 

 if the percent of mice with some form of luxoid 

 and percent of mice with Poly 1 or 2, were 

 compared with parity, trends were apparent. 

 To get a straight line regression was applied 

 giving a positive slope to the luxoid curve 

 and a negative slope to the polydactylous curve. 

 To determine the significance of the curve, a 

 test was applied to the regression coefficient. 

 A positive coefficient of the luxoid slope (r = 

 0.895; d.f.-ll) was significant at the <0.01 level 

 and the negative coefficient of the polydactylous 

 slope (r == -0.792; d.f. -11) was also significant 

 at the <0.01 level. Thus, it is concluded that in- 

 creased parity does not effect the total number of 

 defects but does increase the severity of the 

 morphological defects. 



14.7. Two Unusual Mutations Affecting Pigmenta- 

 tion in the Mouse. H. Glenn-Wolfe (Bar 

 Harbor, U.S.A.). 



A mutation to pink-eyed dilute (/?') that oc- 

 curred in the Production colony of C57BL/6J 

 has been maintained continuously on the same 

 inbred background by cross-intercross to C57BL/ 

 6J. Breeding tests established its allelism, but 

 not its identity with existing pink-eyed dilute 

 (p). An unusual feature is the sporadic occur- 

 rence of mosaic coat-color patterns in mice of 

 genotype p'p\ These vary from a few dark hairs 

 at only one place on the body to heavily mottled 

 animals. Eye color in these same mottled animals 

 ranges from pink eye to full color, and often 

 shows bilateral asymmetry. Mosaics have pro- 



duced wild type progeny in addition to mosaic 

 and normal pink-eyed dilute progeny when 

 test-crossed to non-mottled pp or p'p' animals. 

 In outcrosses of C57BL/6-/?y x \29jRe-pp, 

 deviants varied from light mottled to wild type 

 (8 observed in approximately 3000 classified). 

 Besides effects on pigmentation, />' has been 

 shown to affect the superovulation rate. 



Five mutant animals, borne in two different 

 litters, appeared in the cross C57BL/6J $ x 

 C57BL/6J-A//' wh + $• Mutants are pale yellow 

 with white spots. Breeding tests showed the mu- 

 tant gene to be located at the microphthalmia 

 locus and yellow-spotted animals to beM/ wh w/ sp . 

 An unusual feature of /«/ sp in heterozygous 

 (m/ sp +) or homozygous (/?7/ sp /w' sp ) form is the 

 absence of any visible expression distinguishing 

 it from wild type. Allelic interaction between 

 /w/ sp and Mi Kh or mi is being investigated, 

 particularly effects on pigment granule size and 

 distribution in selected hair types. 



14.8. Inheritance of Leucocyte Counts in Rats. 



W. G. Downs (Cockeville, U.S.A.). 



In an effort to obtain a strain of rats having a 

 consistent leucocyte count, studies have been 

 conducted on the method of inheritance of 

 these counts. Animals were from our own strain 

 of Wistar Sprague-Dawley, out of a Wistar 

 male crossed to four Sprague-Dawley females, 

 then very closely inbred for fifteen or more 

 generations. 



Originally, total leucocyte counts varied 

 between 6800/mm 3 and 17,800/mm 3 . Initially, 

 sixteen crosses were made between animals 

 with a very low count and those with a very high 

 count. Of the 207 of these offspring, 192 had 

 counts between 7900/mm 3 and 15,700/mm 3 . 

 Of these latter animals, 16 crosses were made, 

 and 197 offspring resulted. Of these 178 varied 

 between 9000/mm 3 and 14,200/mm 3 . 



In three successive generations 16 crosses 

 were made, in each instance discarding approxi- 

 mately the 10 per cent of animals at higher and 

 lower extremes. The last, or fifth generation, 

 resulted in 190 offspring whose leucocyte count 

 varied between extremes of 9600/mm 3 and 

 10,900/mm 3 , being fairly evenly distributed be- 

 tween these figures, though with a tendency to 

 concentrate around a mean of 10,400/mm 3 . 

 Considering the inherent error in blood-cell 

 counting, these figures are believed to have 

 attained the initial objective. As the limits of the 

 total count narrowed, so did the differential, 

 as between lymphocytes and granulocytes, the 

 fifth generation having a ratio of 67 per cent 



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