International Journal of Molecular Zoology 2024, Vol.14, No.5, 281-289 http://animalscipublisher.com/index.php/ijmz 282 2.2 Types of heritability (narrow vs. broad) Heritability can be categorized into narrow-sense heritability (h²) and broad-sense heritability (H²). Narrow-sense heritability refers to the proportion of phenotypic variance that is attributable to additive genetic variance alone. This type of heritability is particularly important in predicting the response to selection because it considers only the additive effects of genes, which are directly passed from parents to offspring (Ge et al., 2016; Yang et al., 2017). Broad-sense heritability, on the other hand, includes all genetic variance components, such as additive, dominance, and epistatic variances. It provides a more comprehensive measure of the genetic contribution to phenotypic variance but is less useful for predicting selection response because it includes non-additive genetic effects (Gamma and Liebrenz, 2019). 2.3 Methods for measuring heritability Several methods are used to estimate heritability, each with its own advantages and limitations. Traditional methods often involve studying closely related individuals, such as twins or family members, to partition phenotypic variance into genetic and environmental components. Twin studies, for example, compare the similarity of traits between monozygotic and dizygotic twins to estimate heritability (Sanfilippo et al., 2010). More recently, advances in genomic technologies have enabled the estimation of heritability using genome-wide association studies (GWAS). These studies use single nucleotide polymorphisms (SNPs) to estimate the proportion of phenotypic variance explained by genetic variants across the genome, known as SNP heritability (Speed et al., 2016). Additionally, statistical models such as linear mixed models and structural equation modeling (SEM) are employed to derive heritability estimates from complex datasets, including high-throughput sequencing data (Rudra et al., 2017). Each method has its own set of assumptions and potential sources of bias, making it essential to carefully consider the context and population characteristics when interpreting heritability estimates (Dochtermann et al., 2019). 3 Phenotypic Traits in Bird Populations 3.1 Morphological Traits The size and shape of birds are critical morphological traits that can vary significantly across different species and populations. For instance, a study on ducks revealed that body size is influenced by genetic factors, with specific mutations in the IGF2BP1 gene leading to increased body size and feed efficiency in Pekin ducks (Zhou et al., 2018). Similarly, research on helmeted Guinea fowls in Nigeria showed significant variations in biometric traits such as wing length and body length across different agro-ecological zones, indicating the influence of environmental factors on these morphological traits (Yakubu et al., 2022). Plumage coloration is a highly variable and heritable trait in bird populations, often influenced by genetic and environmental factors. For example, the plumage color of the common barn owl varies with climatic conditions, becoming darker in regions with higher rainfall, which may aid in camouflage and water repellence (Romano et al., 2019). Additionally, the genetic basis of plumage coloration has been extensively studied, with specific genes such as MITFand TYRP1 being associated with color traits in various bird species (Figure 1) (Funk et al., 2022). The interplay between genetic and environmental factors in determining plumage coloration highlights its role in adaptation and speciation. The study of Funk et al. (2022) highlights genetic variation in rosy-finches that influences both their plumage coloration and adaptation to different elevations. The plumage coloration involves genes such as MITF, EDN3, AP3B1, TYRP1, and ASIP, resulting in differences in cheek and crown patch colors. Meanwhile, genes like EGLN1 and ALDH1A1 are crucial for adaptation to high elevations, supporting survival in hypoxic conditions. Unique variations in AGGF1 and JMY are observed in specific high-altitude populations, indicating specialized adaptations beyond shared traits among the finches living in extreme elevations. These genetic variations are key for both aesthetic and environmental adaptations. 3.2 Behavioral Traits Song characteristics are important behavioral traits that can influence mating success and species differentiation. In a study on the limestone wren-babbler, significant bioacoustic differences were found between populations with
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