Section 14 — Animal Genetics and Breeding 



a table, with (say) the rows, M, representing the 

 n kinds of male parent, and the columns, F, the 

 female parents. Analysis of variance gives mean 

 squares for the M, F and MF interaction effects. 

 Alternatively, after adding the M and MF 

 interaction effects. Alternatively, after adding the 

 M and F marginal totals (strain by strain) a mean 

 square a for "additive variation" (parental 

 effects averaged over sex) is obtainable; after a 

 corresponding subtraction of the totals, the 

 differences can yield another mean square c for 

 "maternal effects" (differences between strains 

 when used as male parent and as female parent (0. 

 The MF interaction is further divisible into 

 "mean dominance," etc. In a diallele cross 

 (material of D.S. Falconer and R. C. Roberts) 

 of four large strains of mice selected for high 

 body weight, spermatozoan dimensions studied 

 were: head area in optical projection; maximum 

 head breadth; midpiece length. There was much 

 significant additive variation, with a tendency 

 towards a greater male parent effect than female 

 parent effect. The (log) within-male variance in 

 spermatozoan dimensions showed significant 

 female parent effects and non-significant male 

 parent effects. Difference between parental 

 effects were sometimes reflected as significant 

 "maternal effects". No significance was at- 

 tached to "mean dominance" or any other items 

 within the MF interaction. In a diallele cross of 

 three small strains of mice there were no genetic 

 differences in spermatozoan dimensions. There 

 was no correlated response to selection; sper- 

 matozoan dimensions of small strains in general 

 were similar to those of large strains. A detailed 

 paper will be submitted to Genetical Research 

 (Camb.) 



1. See B. I. Hayman, Biometrics 10, 235-244, 

 1954. 



14.13. (D) Genetics of Reproductive Mechanisms and 

 of Color Variations in the Freshwater Planarian 

 Dugesia lugubris. M. Benazzi and Lentati 

 G. Benazzi (Pisa, Italy). 



Dugesia lugubris presents a diploid amphimic- 

 tic biotype and some polyploid pseudogamous 

 ones, namely: a triploid biotype with ameiotic 

 oocytes, and a triploid biotype with hexaploid 

 meiotic oocytes; the female germ line of the last 

 biotype becomes hexaploid through a chromo- 

 some doubling. The male germ line is always 

 diploid with normal meiosis in all biotypes. 



The genetic background of chromosome 

 cycle of the above mentioned biotypes was 



experimentally analyzed by crossing amphimic- 

 tic diploid specimens, used as females, with 

 pseudogamous polyploid ones. The results 

 obtained have shown that asynapsis, chromo- 

 some doubling in female line and pseudogamy 

 may be transmitted through the sperm, and 

 therefore must be considered as controlled by 

 chromosomal genes. However, the inheritance 

 of such characters is very peculiar, since the 

 oocytes may be both synaptic and asynaptic, 

 diploid and polyploid, amphimictic and pseudo- 

 gamous in the same hybrid; this variable 

 expression of the characters is not easily framed 

 in formal genetics. 



Starting from diploid, asynaptic and am- 

 phimictic Fi it was possible, through repeated 

 crosses or backcrosses, to obtain the 2nd, 3rd 

 and 4th generations, which are triploid, tetra- 

 ploid and pentaploid, respectively. 



Moreover such experimentally produced poly- 

 ploids allow the study of the genetics of the pigmen- 

 tation by crossing differently colored specimens 

 (white and dark respectively). A gradual increase 

 or decrease of the color intensity occurs at each 

 successive generation, related to the increase or 

 decrease of the chromosome sets derived either 

 from the white or the dark parent. This result 

 postulates a cumulative action of the color 

 factors, which can be quantitatively analyzed. 



14.14. Linkage Map of Sex-chromosomes in the 

 Fish, Oryzias latipes. Toki-o Yamamoto 

 (Nagoya, Japan). 



Artificial control of sex differentiation as 

 advanced in Oryzias, where normal sex-deter- 

 mining mechanism isXX=$ andXY= c J, renders 

 it possible to obtain estrogen-induced XY $$ 

 ad libitum. Of 57 sons of induced X r Y R $ x X r Y R 

 <$, where R stands for orange-red colour and 

 /• for its recessive allele, only two proved to be 

 Y R Y R . Y R Y r males, however, are as viable as 

 normal males. All evidence points to the suppo- 

 sition that there is an inert section (-) in the 

 regular Y R and a "viable" section ( — ) in the 

 ordinary X r as well as Y r . 



The linear order in the normal male is ( x ) 

 0.2 r— (+) in the X r or (y) 0.2 R — (— ) in the 

 regular Y and that in the induced X r Y R female 

 is (x) 1.0 r— ( + ) or (y) 1.0 R — (— ), where 

 (x) and (y) stand for non-homologous sex- 

 differentials and the numerals represent observed 

 recombination values. To estimate recom- 

 bination value of the interval r — (+) or R — ( — ), 

 the sum of all fractions relevant to viable Y R Y R 

 of induced X r Y R $ x X r YV is taken as the 

 numerator and the sum of all fractions of 



25; 



