Abstract :
This study investigates the mode of inheritance and estimates the genetic parameters of
milk yield, milk fat content, and litter weight at birth in Chios sheep breed. A complex
pedigree and repeated records for milk and fat content as well as litter weight from two
distinct and unrelated populations, spanning over 20 and 31 years, were used for the detection
of a major gene for milk yield in the Chios breed. The data originated from a closed
nucleus in Northern Greece (6021 repeated records) and from a closed nucleus in Cyprus
(6965 repeated records). The genetic parameters were estimated using both a
polygenic model with maximum likelihood methodology and a mixed inheritance model
(polygenes + major gene), using Bayesian segregation analysis. Segregation analysis results
support the presence of a major gene for milk yield segregating in both populations. The
mixed inheritance model for milk yield appears to be the most suitable model. The estimated
additive effect of the putative major gene was 11% and 10.5% of the total additive
genetic variance in the Cypriot and Greek populations, respectively, while the estimated
dominance effect was negative in both populations. Although there are some indications
for a major gene affecting fat content in Chios breed, there is no evidence for the presence
of a major gene affecting litter weight at birth in either population.
