Animal Molecular Breeding 2024, Vol.14, No.5, 297-306 http://animalscipublisher.com/index.php/amb 299 3 QTL Mapping for Egg Production 3.1 Historical perspectives and early studies Quantitative Trait Loci (QTL) mapping for egg production in layer hens has been a critical research area since the 1990s. Early studies primarily used microsatellite markers to map QTLs associated with egg production traits such as egg number, egg weight, and age at first egg. These early efforts were constrained by the relatively low marker density and limited mapping populations, which resulted in low-resolution maps. Despite these challenges, the identification of QTLs in these early studies provided a foundational understanding of the genetic basis of economically important traits in poultry. Key discoveries include the identification of major QTLs on several chromosomes that affect egg weight and production rate, setting the stage for more advanced genetic analyses using modern techniques (Goto and Tsudzuki, 2017). Figure 1 Histogram of performance traits showing distributions of 446 individually caged ISA Brown hens aged between 25 and 30 weeks for (a) egg produced per hen per day, (b) egg weight, (c) egg mass, (d) average daily feed intake, (e) initial body weight, (f) final body weight, (g) feed conversion ratio, and (h) body weight change (Adapted from Anene et al., 2020) Image caption: Histograms illustrate various performance traits in a population of ISA Brown hens. Traits such as egg weight, egg mass, and body weight exhibit a normal distribution, indicating consistent performance among the flock. However, traits like daily egg production and feed conversion ratio show a skewed distribution, reflecting individual differences within the population. (Adapted from Anene et al., 2020)
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