Polygenic Embryo Selection: Understanding Heritability and Breeder’s Equation

What Polygenic Embryo Selection Is

Polygenic embryo selection is a sophisticated technique in preimplantation genetic testing where embryos are evaluated based on their polygenic scores, which reflect the cumulative effect of multiple genetic variants contributing to a specific trait. This method allows for the prediction and optimization of complex traits such as height or intelligence.

The process involves scoring each embryo against a population bell curve, selecting the top-k embryos with the highest scores, and then applying the breeder's equation R = h²S to estimate the expected change in the mean value of the trait in the offspring.

Why It Happens

The phenomenon behind polygenic embryo selection is rooted in genetics, where traits are influenced by multiple genes. Heritability (h²) quantifies the proportion of variation in a trait that can be attributed to genetic differences among individuals. By selecting embryos with higher scores on this index, breeders aim to enhance desirable traits or reduce disease risks.

The breeder's equation R = h²S provides a mathematical framework for predicting how much selection will affect the mean value of a trait in the next generation. This equation is crucial because it helps in making informed decisions about which embryos to transfer, thereby optimizing the genetic makeup of the offspring.

Heritability and Its Impact

Heritability (h²) is a key parameter in polygenic embryo selection. It represents the degree to which differences in a trait among individuals are due to genetic factors rather than environmental ones. A high heritability value indicates that genetics play a significant role, making it easier to predict and select for specific traits.

For example, if a trait has a high heritability (e.g., 80%), the selection process can be more effective in predicting which embryos will have superior genetic potential for that trait.

Breeder’s Equation: R = h²S

The breeder's equation, R = h²S, is a fundamental concept in quantitative genetics. Here, R represents the expected response to selection (the change in mean value of the trait), h² is the heritability of the trait, and S is the selection differential (the difference between the mean value of the selected individuals and the population mean).

By understanding this equation, breeders can make more accurate predictions about how much a specific trait will improve or deteriorate in the next generation based on their selection choices.

Frequently asked questions

Try it live

Everything above runs in your browser — open Polygenic Embryo Selection: Selection Differential Simulator and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.