GENETIC COMBINING ABILITY OF LIGHT AND HEAVY INBRED LINES IN SINGLE CROSSES OF POULTRY

Abstract

iallel crossing scheme is a method employed to assess the magnitude of TqFeddif€erent types of genetic variability among the crosses of a set of inbred lines. The modified complete diallel involves all crosses (including reciprocals but omitting the parental inbreds) among a random sample of inbred lines from a population of lines. The variation among F, cross means may then be partitioned into general and specific combining ability variances and general and specific reciprocal effect variances. HENDERSON (1948), HAYMAN (1954) and GRIFFING (1956a, 1958) presented the theory underlying the diallel design and analysis. GRIFFING (1956b) and KEMPTHORNE (1956) gave the genetic interpretation of the general and specific combining ability variances estimated from a diallel cross of completely homozygous inbred lines. The theory has been extended by MATZINGER and KEMPTHORNE (1956) to the case where the inbreeding coefficient is arbitrary but constant for all lines. EISEN, BOHREN and MCKEAN (1963) have given the genetic interpretation of general and specific reciprocal effects when the lines are homozygous. The results of diallel experiments with poultry (HILL and NORDSKOG 1958; GOTO and NORDSKOG 1959; MERRITT and GOWE 1960; REDMAN and SHOFFNER 1961; YAO 1961; and WEARDEN et al. 1965) suggest that general combining ability variance is the single most important source of genetic variation for most traits, but that specific combining ability and reciprocal effect variances may be important for some traits. The major objective of the present study was to assess the types of genetic variability present for 13 traits among the crosses of a random set of four White Leghorn (light type) and four heavy type inbred lines. MATERIALS AND METHODS The data used for this investigation were collected at the North Central Regional Poultry Breeding Laboratory, Lafayette, Indiana over a period of three years. The inbred lines employed and their respective inbreeding coefficients are given in Table 1. The average inbreeding coefi