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Population Genetics

Population genetics Genetics Genetics is the study of genes and their functions and behaviors. Basic Terms of Genetics is a field in genetics Genetics Genetics is the study of genes and their functions and behaviors. Basic Terms of Genetics that is concerned with the differences in the gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics pool between different populations and how this underlies phenotypic differences between populations. The Hardy-Weinberg equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy serves as a basis for studying genetic variation within a population and allows for the calculation of allelic frequency. The process of natural selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions is what determines the allelic frequencies in the population and the variability in the genotype Genotype The genetic constitution of the individual, comprising the alleles present at each genetic locus. Basic Terms of Genetics- phenotype Phenotype The complete genetic complement contained in the DNA of a set of chromosomes in a human. The length of the human genome is about 3 billion base pairs. Basic Terms of Genetics relationships between species.

Last updated: 29 Apr, 2022

Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Hardy-Weinberg Equilibrium

Introduction

Population genetics Genetics Genetics is the study of genes and their functions and behaviors. Basic Terms of Genetics studies genetic variation within a group.

  • Depends on genetic, environmental, and societal factors
  • These factors determine the frequency and distribution of alleles and genotypes.

A given population possesses a common gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics pool.

  • May contain several alleles of 1 gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics
  • Relative proportions of these alleles are referred to as gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics frequency.

Gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure is created when individuals migrate into or away from the population.

Definition

The Hardy-Weinberg equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy says that within a given population, both allele Allele Variant forms of the same gene, occupying the same locus on homologous chromosomes, and governing the variants in production of the same gene product. Basic Terms of Genetics and genotype Genotype The genetic constitution of the individual, comprising the alleles present at each genetic locus. Basic Terms of Genetics frequencies remain constant, without evolutionary influences.

Assumptions of the Hardy-Weinberg equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy

The Hardy-Weinberg equilibrium Equilibrium Occurs when tumor cells survive the initial elimination attempt These cells are not able to progress, being maintained in a state of dormancy by the adaptive immune system. In this phase, tumor immunogenicity is edited, where T cells keep selectively attacking highly immunogenic tumor cells.This attack leaves other cells with less immunogenicity to potentially develop resistance to the immune response. Cancer Immunotherapy relies on 7 assumptions:

  • Organisms must be diploid Diploid The chromosomal constitution of cells, in which each type of chromosome is represented twice. Symbol: 2n or 2x. Basic Terms of Genetics.
  • Sexual reproduction produces new members of the population (no migration).
  • Generations do not overlap.
  • Random mating (without selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions)
  • Infinitely large population size
  • Allele Allele Variant forms of the same gene, occupying the same locus on homologous chromosomes, and governing the variants in production of the same gene product. Basic Terms of Genetics frequencies are equal between the sexes.
  • Within a population, there is no gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure or mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations.

Evolutionary influences

  • Genetic drift: Random sampling of organisms leads to a change in genetic frequency.
  • Assortative mating: Individuals with similar phenotypes mate more commonly.
  • Natural selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions: Phenotypes that provide an advantage perpetuate an increased frequency of the corresponding genotype Genotype The genetic constitution of the individual, comprising the alleles present at each genetic locus. Basic Terms of Genetics.
  • Sexual selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions: a drive to mate with the opposite sex Sex The totality of characteristics of reproductive structure, functions, phenotype, and genotype, differentiating the male from the female organism. Gender Dysphoria for reproductive purposes
  • Mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations: change in nucleotide sequence
  • Gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure: transfer of genetic material between populations
  • Meiotic drive: 1 allele Allele Variant forms of the same gene, occupying the same locus on homologous chromosomes, and governing the variants in production of the same gene product. Basic Terms of Genetics may be favored to be passed.
  • Population bottleneck: event that reduces population (e.g., natural disaster)
  • Inbreeding: mating between individuals or organisms that are closely related
  • Founder effect: a new population leading to a decrease in genetic variation

Hardy-Weinberg Equation

Introduction

The Hardy-Weinberg equation allows for the calculation of genetic variation of a population.

  • This equation relies on the assumption that genetic variation in a population will remain constant between generations.
  • Permits a genetic locus Locus Specific regions that are mapped within a genome. Genetic loci are usually identified with a shorthand notation that indicates the chromosome number and the position of a specific band along the P or Q arm of the chromosome where they are found. For example the locus 6p21 is found within band 21 of the P-arm of chromosome 6. Many well known genetic loci are also known by common names that are associated with a genetic function or hereditary disease. Basic Terms of Genetics to have 2 alleles
  • The Hardy-Weinberg equation relies on the absence of sexual selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions, the absence of genetic flow Flow Blood flows through the heart, arteries, capillaries, and veins in a closed, continuous circuit. Flow is the movement of volume per unit of time. Flow is affected by the pressure gradient and the resistance fluid encounters between 2 points. Vascular resistance is the opposition to flow, which is caused primarily by blood friction against vessel walls. Vascular Resistance, Flow, and Mean Arterial Pressure or mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations, and a large population such that the probabilities are equal to the frequencies.

Equation

The Hardy-Weinberg equation:

$$p^{2}+2pq+q^{2}=1$$
  • Components:
    • The “p” stands for the frequency of 1 allele Allele Variant forms of the same gene, occupying the same locus on homologous chromosomes, and governing the variants in production of the same gene product. Basic Terms of Genetics and “q” stands for the frequency of the other allele Allele Variant forms of the same gene, occupying the same locus on homologous chromosomes, and governing the variants in production of the same gene product. Basic Terms of Genetics.
    • Genotype Genotype The genetic constitution of the individual, comprising the alleles present at each genetic locus. Basic Terms of Genetics AA AA Amyloidosis: frequency p2
    • Genotypes Aa AA Amyloidosis, aA AA Amyloidosis: frequency 2pq
    • Genotype Genotype The genetic constitution of the individual, comprising the alleles present at each genetic locus. Basic Terms of Genetics aa AA Amyloidosis: frequency q2
  • With the aid of the Hardy-Weinberg equation, population geneticists are able to calculate what percentage of a certain disease is contained in a gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics. If gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics A and gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics a are distributed in a population that is constant, the following applies: 
$$p+q=1 (=100\%)$$

Sample calculation

In a population, the dominant allele Allele Variant forms of the same gene, occupying the same locus on homologous chromosomes, and governing the variants in production of the same gene product. Basic Terms of Genetics is present with a frequency of 60% in the gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics pool. What is the distribution of the possible genotypes within the population?

  • p = 60%, q = 40%, because q + p = 100%
  • p2 + 2pq + q2 = 1
  • (0.6)2 + 2 × (0.6 × 0.4) + (0.4)2 = 1
  • 0.36 + 0.48 + 0.16 = 1
  • p2 = 36%, pq = 48%, q2 = 16
  • Answer: AA AA Amyloidosis is 36%; Aa AA Amyloidosis is 48%, and aa AA Amyloidosis is 16%.
Hardy-weinberg proportions

The calculated Hardy-Weinberg proportions given 2 alleles in a genetic pool

Image by Lecturio.

Natural Selection

  • Over longer periods of time, the gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics pool of a population changes via several mechanisms, most commonly natural selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions.
  • Natural selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions favors individuals with a genetic composition that improves the chances of survival and reproduction:
    • A trait that gives a reproductive advantage will be passed down at a higher rate than traits that do not give a reproductive advantage.
    • These genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure will occupy a growing share of the gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics pool over time.
    • If the genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure that offer survival advantages are dominant, they spread rapidly.
    • Dominant genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure that are disadvantageous to the individual disappear quickly.
    • Recessive genes Genes A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. DNA Types and Structure persist longer in a population.
Natural selection

An example of natural selection Selection Lymphocyte activation by a specific antigen thus triggering clonal expansion of lymphocytes already capable of mounting an immune response to the antigen. B cells: Types and Functions occurring in bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology to perpetuate antibiotic resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing

Image: “Antibiotic resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing” by Wykis. License: Public Domain

Clinical Relevance

  • Sickle cell anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types: an example of a regionally frequent gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics defect that offers its carriers Carriers The Cell: Cell Membrane a selective advantage. Sickle cell anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types is especially prevalent in sub-Saharan Africa, where around 80% of the disease occurs. Sickle cell anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview and Types is an autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritance condition. Heterozygous carriers Carriers The Cell: Cell Membrane, who carry the HbS HbS An abnormal hemoglobin resulting from the substitution of valine for glutamic acid at position 6 of the beta chain of the globin moiety. The heterozygous state results in sickle cell trait, the homozygous in sickle cell anemia. Sickle Cell Disease gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics, have a higher resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing to malaria Malaria Malaria is an infectious parasitic disease affecting humans and other animals. Most commonly transmitted via the bite of a female Anopheles mosquito infected with microorganisms of the Plasmodium genus. Patients present with fever, chills, myalgia, headache, and diaphoresis. Plasmodium/Malaria than non- carriers Carriers The Cell: Cell Membrane do. Thus, through selective advantage, the carriers Carriers The Cell: Cell Membrane in malaria Malaria Malaria is an infectious parasitic disease affecting humans and other animals. Most commonly transmitted via the bite of a female Anopheles mosquito infected with microorganisms of the Plasmodium genus. Patients present with fever, chills, myalgia, headache, and diaphoresis. Plasmodium/Malaria-endemic regions receive a high share of the HbS HbS An abnormal hemoglobin resulting from the substitution of valine for glutamic acid at position 6 of the beta chain of the globin moiety. The heterozygous state results in sickle cell trait, the homozygous in sickle cell anemia. Sickle Cell Disease gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics in the gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics pool of the population. These heterozygous individuals are able to produce enough hemoglobin for normal function while receiving the benefit of less- severe malaria Severe malaria Plasmodium/Malaria infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
  • Tay-Sachs disease Tay-Sachs disease Tay-Sachs disease is an autosomal recessive lysosomal storage disorder caused by genetic mutations in the hexosaminidase A (HEXA) gene, leading to progressive neurodegeneration. Classic symptoms in infants include rapid degeneration of cognitive and neuromuscular abilities, progressive blindness, and a macular cherry-red spot on physical examination. Tay-Sachs Disease: founder effect is displayed through Tay-Sachs disease Tay-Sachs disease Tay-Sachs disease is an autosomal recessive lysosomal storage disorder caused by genetic mutations in the hexosaminidase A (HEXA) gene, leading to progressive neurodegeneration. Classic symptoms in infants include rapid degeneration of cognitive and neuromuscular abilities, progressive blindness, and a macular cherry-red spot on physical examination. Tay-Sachs Disease. The founder effect is seen when a smaller group isolates itself from a population, splits off, and reproduces, thereby decreasing genetic variation. Ashkenazi Jews have a higher-than-normal chance of Tay-Sachs disease Tay-Sachs disease Tay-Sachs disease is an autosomal recessive lysosomal storage disorder caused by genetic mutations in the hexosaminidase A (HEXA) gene, leading to progressive neurodegeneration. Classic symptoms in infants include rapid degeneration of cognitive and neuromuscular abilities, progressive blindness, and a macular cherry-red spot on physical examination. Tay-Sachs Disease and other lipid storage disorder, which is partially attributed to the high incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency of a certain chromosome Chromosome In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. Basic Terms of Genetics with a high allele Allele Variant forms of the same gene, occupying the same locus on homologous chromosomes, and governing the variants in production of the same gene product. Basic Terms of Genetics frequency in the early founding population.
  • Antibiotic resistance Resistance Physiologically, the opposition to flow of air caused by the forces of friction. As a part of pulmonary function testing, it is the ratio of driving pressure to the rate of air flow. Ventilation: Mechanics of Breathing: commonly occurs through horizontal gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics transfer, which refers to the exchange of genetic information from 1 organism to another. Horizontal transfer of genetic information occurs between concurrently living organisms, not through sexual reproduction.

References

  1. Griffiths, AJF, Miller, JH, Suzuki, DT, et al. (2000). Chapter 24: Population genetics. In An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman. https://www.ncbi.nlm.nih.gov/books/NBK21961/
  2. Charlesworth, B, & Charlesworth, D. (2017). Population genetics from 1966 to 2016. Heredity. 118(1), 2–9. https://doi.org/10.1038/hdy.2016.55
  3. Casillas, S, & Barbadilla, A. (2017). Molecular population genetics. Genetics. 205(3), 1003–1035. https://doi.org/10.1534/genetics.116.196493
  4. Belsky, DW, Moffitt, TE, & Caspi, A. (2013). Genetics in population health science: Strategies and opportunities. American Journal of Public Health. 103 Suppl 1(Suppl 1), S73–S83. https://doi.org/10.2105/AJPH.2012.301139

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