Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

21. Population Genetics

Allelic Frequency Changes

Genetics

21. Population Genetics

Allelic Frequency Changes

Previous problemNext problem

1:53 minutes

Problem 22b

Textbook Question

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. Explain how a genetic bottleneck and its aftermath could result in a population that carries a lethal allele in high frequency.

Verified step by step guidance

A genetic bottleneck occurs when a population undergoes a drastic reduction in size due to events such as natural disasters, disease outbreaks, or human actions like genocide. This reduction limits genetic diversity because only a small subset of individuals survive and reproduce.

During a bottleneck, alleles present in the surviving population may become disproportionately represented, regardless of whether they are beneficial, neutral, or harmful. This is due to random chance rather than natural selection.

If the surviving population includes individuals carrying a lethal recessive allele (such as the Tay–Sachs allele), the frequency of this allele can increase in the population simply because it is present in the reduced gene pool.

After the bottleneck, the population may begin to grow again, but the genetic diversity remains limited. The previously rare lethal allele may persist at a higher frequency because there is less genetic variation to dilute its presence.

In subsequent generations, the allele frequency can remain high, especially if the population remains relatively isolated (e.g., through cultural or geographic factors) and interbreeding within the group continues. This phenomenon is known as genetic drift, which can amplify the effects of the bottleneck over time.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Genetic Bottleneck

A genetic bottleneck occurs when a population experiences a significant reduction in size due to environmental events or human activities, leading to a loss of genetic diversity. This reduction can result in certain alleles becoming more prevalent in the surviving population, as the genetic variation is limited to the alleles present in the few individuals that survive. Consequently, harmful alleles, such as those causing Tay-Sachs disease, can persist at higher frequencies.

Autosomal Recessive Inheritance

Autosomal recessive inheritance refers to a pattern 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, individuals must inherit the defective allele from both parents to develop the condition. This means that carriers, who possess only one copy of the allele, do not show symptoms but can pass the allele to their offspring, allowing the allele to remain in the population.

Founder Effect

The founder effect is a phenomenon that occurs when a small group of individuals establishes a new population, leading to a limited genetic pool. If the founders carry certain alleles, including those for genetic disorders, these alleles can become more common in the new population due to the reduced genetic diversity. In the context of Ashkenazi Jews, historical events that led to population bottlenecks may have resulted in a higher frequency of the Tay-Sachs allele among descendants.

Watch next

Master Natural Selection with a bite sized video explanation from Kylia

Start learning

Related Videos

Related Practice

Textbook Question

A farmer plants transgenic Bt corn that is genetically modified to produce its own insecticide. Of the corn borer larvae feeding on these Bt crop plants, only 10 percent survive unless they have at least one copy of the dominant resistance allele B that confers resistance to the Bt insecticide. When the farmer first plants Bt corn, the frequency of the B resistance allele in the corn borer population is 0.02. What will be the frequency of the resistance allele after one generation of corn borers have fed on Bt corn?

473

views

Textbook Question

In an isolated population of 50 desert bighorn sheep, a mutant recessive allele c when homozygous causes curled coats in both males and females. The normal dominant allele C produces straight coats. A biologist studying these sheep counts four with curled coats. She also takes blood samples from the population for DNA analysis, which reveals that 17 of the sheep are heterozygous carriers of the c allele. What is the inbreeding coefficient F for this population?

411

views

Textbook Question

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. Assuming mating occurs at random in this population, what is the probability a couple are both carriers of Tay–Sachs disease?

364

views

Textbook Question

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. In the population described, what is the frequency of the recessive allele that produces Tay–Sachs disease?

To increase genetic diversity in the bighorn sheep population described in Problem 23, ten sheep are introduced from a population where the c allele is absent. Assuming that random mating occurs between the original and the introduced sheep, and that the c allele is selectively neutral, what will be the frequency of c in the next generation?

444

views

Textbook Question

What genetic changes take place during speciation?

445

views

Textbook Question

List the barriers that prevent interbreeding, and give an example of each.

354

views

Show more practices