Genetic variation, which is generated by mutation, recombination and gene flow, can reduce the mean fitness of a population, both now and in the future. This ‘genetic load’ has been estimated in a wide range of animal taxa using various approaches. Advances in genome sequencing and computational techniques now enable us to estimate the genetic load in populations and individuals without direct fitness estimates. Here, we review the classic and contemporary literature of genetic load. We describe approaches to quantify the genetic load in whole-genome sequence data based on evolutionary conservation and annotations. We show that splitting the load into its two components — the realized load (or expressed load) and the masked load (or inbreeding load) — can improve our understanding of the population genetics of deleterious mutations.

由突变、重组和基因流动产生的遗传变异会降低种群的平均适应度，无论是现在还是将来。这种“遗传负荷”已经使用各种方法在广泛的动物分类群中进行了估计。基因组测序和计算技术的进步现在使我们能够在没有直接适应度估计的情况下估计群体和个体的遗传负荷。在这里，我们回顾了遗传负荷的经典和当代文献。我们描述了基于进化保守和注释来量化全基因组序列数据中遗传负荷的方法。我们表明，将负载分为两个部分——实际负载（或表达负载）和掩蔽负载（或近亲繁殖负载）——可以提高我们对有害突变的群体遗传学的理解。