Episode 146: Mendelian Genetics and Inheritance

Heritability

Heritability is a key concept in genetics, estimating how much of the variation in a phenotypic trait is due to genetic variation. James Fodor explains the difference between broad-sense and narrow-sense heritability, emphasizing that broad-sense heritability includes all genetic variance, while narrow-sense focuses on additive genetic variance 1. This distinction is crucial for understanding how traits are inherited and predicted in offspring.

Broad sense heritability is the proportion of all the variation in the phenotype that's explained by the genotypic variation.

--- James Fodor

Narrow-sense heritability, on the other hand, is more practical for predicting offspring traits but often lower due to complex gene interactions 2.

   

Quantitative Traits

Quantitative trait studies use advanced methods like genome-wide association studies (GWAS) to identify genetic loci linked to traits. James Fodor describes how GWAS works by sequencing genomes and looking for correlations between single nucleotide polymorphisms (SNPs) and traits 3. Despite initial challenges, recent advancements have led to more robust and replicable results.

These genome-wide association studies are kind of the state of the art when it comes to trying to determine the genetic basis for quantitative traits.

--- James Fodor

However, many traits are highly polygenic, involving hundreds or thousands of genes, making the research complex and requiring large sample sizes 4.

   

Polygenic Traits

Polygenic traits are influenced by multiple genes, each contributing a small effect. James Fodor explains that these traits often involve rare allelic variants and complex gene interactions, both with each other and the environment 5. This complexity makes it difficult to study and predict phenotypes accurately.

Traits are highly polygenic, not just determined by a small number of genes, but many, many genes, like hundreds of genes or even thousands.

--- James Fodor

Additionally, the interaction effects mean that even small genetic differences can lead to significant phenotypic variations, complicating the study of these traits 6.