Tay–Sachs disease is an autosomal recessive neurological disorder that is fatal in infancy. Despite its invariably lethal effect, Tay–Sachs disease occurs at very high frequency in some Central and Eastern European (Ashkenazi) Jewish populations. In certain Ashkenazi populations, 1 in 750 infants has Tay–Sachs disease. Population biologists believe the high frequency is a consequence of genetic bottlenecks caused by pogroms (genocide) that have reduced the population multiple times in the past several hundred years. What is a genetic bottleneck?

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1. A genetic bottleneck is a sharp reduction in the size of a population due to environmental events or human activities, such as natural disasters, disease outbreaks, or genocide.
2. During a bottleneck, the genetic diversity of the population decreases because only a small subset of individuals survive and reproduce, passing on their genetic material to future generations.
3. This reduction in genetic diversity can lead to an increased frequency of certain alleles, including those associated with genetic disorders, as the surviving population may not represent the original genetic variation of the group.
4. In the case of Tay–Sachs disease, the genetic bottlenecks experienced by Ashkenazi Jewish populations likely amplified the frequency of the recessive allele responsible for the disorder.
5. Understanding genetic bottlenecks is important in population genetics because they can have long-term effects on the genetic health and evolutionary trajectory of a population.

Key Concepts

Genetic Bottleneck

A genetic bottleneck occurs when a population's size is significantly reduced for at least one generation, leading to a loss of genetic diversity. This reduction can result from events such as natural disasters, disease outbreaks, or human actions, which drastically decrease the number of individuals in a population. The surviving population may not represent the genetic diversity of the original group, potentially leading to increased prevalence of certain genetic traits or disorders.

Autosomal Recessive Inheritance

Autosomal recessive inheritance is a pattern of genetic transmission where two copies of a mutated gene, one from each parent, are necessary for an individual to express a trait or disorder. In the case of Tay–Sachs disease, both parents must be carriers of the mutated gene for their child to be affected. This mode of inheritance can lead to higher frequencies of the disorder in populations where carriers are more common, often due to historical factors like genetic bottlenecks.

Population Genetics

Population genetics is the study of genetic variation within populations and how these variations change over time due to factors like natural selection, genetic drift, mutation, and gene flow. It helps explain the distribution of genetic traits and diseases in populations, such as the high incidence of Tay–Sachs disease in Ashkenazi Jews, which can be attributed to historical events that shaped their genetic landscape, including bottlenecks and founder effects.