Dictionary — 167 — Formulae 



Ratios : 



F, (4n-l):l 



Backcross (2" — 1) :1 



where n is the number of factors involved. 



The proportion of homozygotes to heterozygotes in a population 



mating at random is given by 



p2 : 2pq : g' 



where p^ and q"^ are the proportions of the two homozygous classes 

 respectively, 2pq represents the proportion of heterozygotes and 

 ^ + 9=1. The full F2 ratio (with dominance) is given by cal- 

 culating (3 + \)^ e.g. 2 factor pairs would give (3 + 1)2 = 

 9:3:3:1; 3 factors give (3 + 1)3 = 27:9:9:9:3:3:3:1. 



Recombination Fraction. — The formulae for the gametic output 

 of the double heterozygote AaBb are (i) Coupling: Yiil — /')AB, 

 i^Mb, J^Z-aB, >^(1— /))ab; (ii) Repulsion: HMB, J4(l— /')Ab, 

 J4(l — /')aB, Y2p3h, where p represents the recombination fraction. 

 Where there is no linkage, p = 0.5. 



Relationship Coefficient. — A measure of the degree of relation- 

 ship existing between any two individuals. The general formula is : 



^ ^[^"^"'(1 + F„)] 



'" V(l+F.)(l+n) 

 i?jj,y is the relationship coefficient of two individuals X and Y. 

 n is the number of generations X is removed from the common 



ancestor A. 

 n' is the number of generations Y is removed from the common 



ancestor A, 



F^ is the inbreeding coefficient of X (q.v.), 

 Fy is the inbreeding coefficient of Y (q.v.), 

 F^ is the inbreeding coefficient of A. 



Standard Deviation (a) : 





where S stands for summation, d is the difference between an 

 observation and the mean and n is the total number of observations. 



Variance (a^). — See under Standard Deviation (above). The 

 standard deviation is the square-root of the variance. 



