1.2 - Allele Frequency
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Introduction to Gene Pools and Allele Frequency
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Today, weβre going to talk about gene pools and allele frequency. Letβs start with the term 'gene pool.' Can anyone tell me what a gene pool is?
I think itβs like all the genes that a group of organisms can pass on to their offspring?
Exactly! A gene pool includes all the different genes and their alleles in an interbreeding population. Now, how about allele frequency? How do we calculate that?
By counting how many times a particular allele appears?
Correct! We use the formula: Number of copies of the specific allele divided by the total number of alleles for that gene. Can anyone give me an example?
If there are 160 A alleles and 40 a alleles in a population of 100, thatβs 200 alleles total, so A would be 0.8?
Yes! Great example. Remember, allele frequency helps us understand genetic diversity in populations.
Evolution and Changes in Allele Frequency
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Now that we understand allele frequency, let's discuss how evolution impacts it. Can anyone name some factors that can change allele frequencies over time?
Mutation introduces new alleles, right?
Exactly! What else?
Gene flow, when alleles move between populations?
Right again! We also have genetic drift, particularly in small populations. What do we mean by natural selection?
Natural selection is when individuals better adapted to their environment survive and reproduce more.
Yes! And sexual selection can also influence allele frequency based on mate preferences. Important concepts!
Hardy-Weinberg Principle and Its Applications
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Letβs dive into the Hardy-Weinberg Principle, which states that allele and genotype frequencies remain constant in a population without evolutionary influences. What are the conditions for this equilibrium?
Large population size, random mating, no mutations, no migration, and no natural selection?
Correct! If these conditions are met, the frequencies help us predict carriers for genetic traits. Why might these numbers change?
Because in real life, those conditions arenβt always met, right?
Exactly! Deviations indicate an evolutionary change is occurring. Always check those conditions!
Introduction & Overview
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Quick Overview
Standard
This section explores allele frequency, which quantifies allele prevalence in a population's gene pool. It covers the calculation of allele frequency, evolutionary forces influencing these frequencies, and the significance of genetic diversity for population survival. Understanding allele frequency is key to grasping concepts in evolutionary biology.
Detailed
Allele Frequency
Overview
Allele frequency is a fundamental concept in genetics and population biology that measures how common a particular allele is within a gene pool of an interbreeding population. This section delves into the definition of a gene pool, how to calculate allele frequency, the evolutionary significance of allele changes, and the Hardy-Weinberg Principle.
Key Concepts
- Gene Pool: Refers to the total collection of genes and their alleles within a population. High genetic diversity (a large gene pool) allows for better adaptation and reduces extinction risk, while low diversity makes populations more susceptible to diseases.
- Allele Frequency: Calculated by the formula:
\[ \text{Allele Frequency} = \frac{\text{Number of copies of the specific allele}}{\text{Total number of all alleles for that gene in the population}} \]
For example, if an allele A appears 160 times in a population of 100 individuals, the frequency of A would be 0.8, while that of its counterpart a would be 0.2.
3. Evolution and Changes in Allele Frequency: Evolution results from changes in allele frequencies over generations influenced by factors like mutation, gene flow, genetic drift, natural selection, and sexual selection.
4. Hardy-Weinberg Equilibrium: This principle states that allele and genotype frequencies remain constant in a population under certain conditions (large size, random mating, no mutation, migration, or natural selection).
5. Applications of Allele Frequencies: Understanding allele frequencies helps in predicting genetic disease carriers and examining evolutionary changes that deviate from expected frequencies.
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Definition of Allele Frequency
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Chapter Content
Allele frequency refers to how common a particular allele is within a gene pool. It is calculated using the formula:
$$\text{Allele Frequency} = \frac{\text{Number of copies of the specific allele}}{\text{Total number of all alleles for that gene in the population}}$$
Detailed Explanation
Allele frequency is a measure of how prevalent a specific allele is within a population's gene pool. It helps us understand the genetic diversity of a population. To calculate it, you divide the number of copies of a specific allele by the total number of alleles for that gene. This gives a fraction that represents the frequency of the allele.
Examples & Analogies
Think of a bag of colored marbles representing a population: If you have 160 red marbles and 40 blue marbles, you can find the frequency of the red marbles by dividing the number of red marbles (160) by the total number of marbles (200). This is similar to calculating the allele frequency in a population.
Calculating Allele Frequency: An Example
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Chapter Content
For example, if a gene has two alleles, A and a, and in a population of 100 individuals (each with two alleles), there are 160 A alleles and 40 a alleles:
Frequency of A = $$\frac{160}{200} = 0.8$$
Frequency of a = $$\frac{40}{200} = 0.2$$
Detailed Explanation
In this example, we have a population of 100 individuals where each individual has two alleles. There are 160 copies of allele A and 40 copies of allele a. To find the frequency of allele A, we calculate 160 divided by the total of 160 + 40 (which is 200). The result, 0.8, shows that 80% of the alleles in the population are A. For allele a, we use a similar calculation, resulting in a frequency of 0.2 or 20%.
Examples & Analogies
Imagine a class of students where 80% of students prefer one subject over another. If you count 80 students favoring math (A) and 20 favoring art (a), you can say most students favor math, similar to how allele frequencies indicate which alleles are more common in a population.
Factors Influencing Allele Frequencies
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Chapter Content
Evolution involves changes in allele frequencies over time. Factors influencing these changes include:
β Mutation: Introduces new alleles into the gene pool.
β Gene Flow: Movement of alleles between populations through migration.
β Genetic Drift: Random changes in allele frequencies, especially in small populations.
β Natural Selection: Differential survival and reproduction of individuals based on advantageous traits.
β Sexual Selection: Preference for certain traits during mate selection, affecting allele frequencies.
Detailed Explanation
Several factors can cause changes in allele frequencies in a population over time. Mutation is the creation of new alleles, which can introduce genetic variation. Gene flow occurs when individuals from other populations migrate and breed, changing allele frequencies. Genetic drift refers to random changes in allele frequencies that can have a larger effect on small populations. Natural selection favors individuals with traits that enhance survival and reproduction, leading to changes in allele frequencies. Sexual selection influences which traits are passed on based on mate preferences.
Examples & Analogies
Consider a wildlife reserve where a disease affects the majority of rabbits. Only the rabbits that are naturally resistant survive (natural selection), leading to a shift in allele frequency towards resistance. Meanwhile, if new rabbits come in from another area (gene flow), or if a few rabbits randomly die off (genetic drift), these also change the genetic makeup of the population over time.
Key Concepts
-
Gene Pool: Refers to the total collection of genes and their alleles within a population. High genetic diversity (a large gene pool) allows for better adaptation and reduces extinction risk, while low diversity makes populations more susceptible to diseases.
-
Allele Frequency: Calculated by the formula:
-
\[ \text{Allele Frequency} = \frac{\text{Number of copies of the specific allele}}{\text{Total number of all alleles for that gene in the population}} \]
-
For example, if an allele A appears 160 times in a population of 100 individuals, the frequency of A would be 0.8, while that of its counterpart a would be 0.2.
-
Evolution and Changes in Allele Frequency: Evolution results from changes in allele frequencies over generations influenced by factors like mutation, gene flow, genetic drift, natural selection, and sexual selection.
-
Hardy-Weinberg Equilibrium: This principle states that allele and genotype frequencies remain constant in a population under certain conditions (large size, random mating, no mutation, migration, or natural selection).
-
Applications of Allele Frequencies: Understanding allele frequencies helps in predicting genetic disease carriers and examining evolutionary changes that deviate from expected frequencies.
Examples & Applications
In a population of 100 individuals with 160 A alleles and 40 a alleles, the allele frequency for A is 0.8 and for a is 0.2.
Mutation introduces new alleles, changing allele frequencies and influencing evolution.
Memory Aids
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Rhymes
In a gene pool, alleles do flow, how often they are found will surely show!
Stories
Imagine a village where everyone shares their plants. Some plants are tall, others short. The tall ones survive storms better, so more tall plants grow each season. This story illustrates natural selection affecting allele frequencies.
Memory Tools
M-GNE-NI: Mutation, Gene Flow, Natural Selection, Genetic Drift, and Sexual Selection β the factors influencing allele frequencies.
Acronyms
HARDY
Huge population
All alleles accounted
Random mating
No mutations
No migration
No selection β conditions for Hardy-Weinberg.
Flash Cards
Glossary
- Gene Pool
The total collection of genes and their alleles found within a population.
- Allele Frequency
The relative frequency of a particular allele in a population's gene pool.
- Evolution
The change in allele frequencies within a population over generations.
- HardyWeinberg Equilibrium
A principle stating that allele and genotype frequencies remain constant in a population under specific conditions.
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