Hardy Weinberg Principle
Hardy Weinberg Principle - Related Videos
06:19
Hardy-Weinberg and Genetic Drift - Concepts
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2019
Evolutionary change is interesting and important to study, but changes in populations occur over long periods of time and in huge physical spaces and are therefore very difficult to measure. In general, studying phenomena like this requires the use of mathematical models which are built using parameters that can be conveniently measured. These models are then used to make predictions about how changes to the system might affect the outcome. For example, changes to the frequency of genetic...
01:53
Hardy-Weinberg and Genetic Drift - Instructor Prep
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2019
Mathematical ModelingExpand Before beginning the mathematical modeling exercise make sure each computer has access to an either on or offline spreadsheet software program. Simulation for Hardy-Weinberg and Genetic DriftExpand Prepare one set of beads for each pair of students by counting out 50 of one color and then 50 of a second color, for a total of 100 beads. Then, place the beads in a paper bag. Students will also need extra beads to adjust the...
15:42
Hardy-Weinberg and Genetic Drift - Student Protocol
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2019
Class Simulation ExpandBegin by opening a new spreadsheet file. Following the Hardy-Weinberg equation where p is the frequency of a dominant allele A in a population, and q is defined as the frequency of a recessive allele B, input frequency p of allele A into cell B2, and frequency q of allele B into cell B3. Assign the value 0.5 to cell C2. Following the 1 – p = q equation, enter the formula “= 1 – C2” into cell C3 to calculate the frequency q of allele B. NOTE: Cells C2 and C3 will represent...
01:49
Hardy-Weinberg Principle
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2026
Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.In the early 20th century,...
08:37
Le Châtelier's Principle
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2023
Source: Laboratory of Dr. Lynne O'Connell — Boston College When the conditions of a system at equilibrium are altered, the system responds in such a way as to maintain the equilibrium. In 1888, Henri-Lewis Le Châtelier described this phenomenon in a principle that states, "When a change in temperature, pressure, or concentration disturbs a system in chemical equilibrium, the change will be counteracted by an alteration in the equilibrium composition." This experiment demonstrates Le Châtelier's...
FAQs
The symbols p and q represent the frequencies of two alleles, while p², 2pq, and q² represent the expected frequencies of the two homozygous genotypes and the heterozygous genotype. Because these genotype frequencies are derived from allele frequencies, researchers can use allele data to estimate the genetic composition expected in the next generation.
Random mating allows allele combinations to form according to their population frequencies rather than through consistent mating preferences. A large population reduces the influence of chance changes in allele frequency. Together, these conditions support stable genotype-frequency expectations and make departures from the model more informative when evaluating whether a population may be evolving.
A difference between observed and expected genotype frequencies suggests that one or more equilibrium conditions may not hold. The comparison can therefore point to evolutionary forces such as mutation, migration, or natural selection, although the model identifies a departure from expectation rather than automatically determining which force caused it.
The principle provides a reference pattern for a population in which allele frequencies remain unchanged across generations. If measured frequencies match the expected pattern, the available data are consistent with equilibrium conditions. If they differ, researchers have evidence that population structure or an evolutionary process may be affecting genetic variation.
Researchers first identify allele frequencies from population observations, then calculate expected genotype frequencies using p², 2pq, and q². They compare those expectations with the genotypes actually recorded. This workflow helps assess genetic variation and reveals whether the population data fit the model or show evidence of evolutionary change.
In inheritance studies, the model links allele frequencies to expected genotype proportions, providing a quantitative framework for examining genetic patterns. In population-structure research, comparing expected and observed frequencies helps identify departures associated with how genetic variation is distributed. These uses make the principle a baseline for interpreting population-level biological data.