Back To Course

TExES Life Science 7-12 (238): Practice & Study Guide32 chapters | 254 lessons | 28 flashcard sets

Are you a student or a teacher?

Try Study.com, risk-free

As a member, you'll also get unlimited access to over 75,000 lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed.

Try it risk-freeWhat teachers are saying about Study.com

Already registered? Log in here for access

Your next lesson will play in
10 seconds

Lesson Transcript

Instructor:
*Angela Hartsock*

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

In this lesson we will define Hardy-Weinberg equilibrium and break down the Hardy-Weinberg equation to figure out if a population of hypothetical beetles is evolving.

Let's say we're studying a large group of beetles, 86% of which are green, 14% are brown. What will the percentage be in future generations? Why? Now we're thinking in terms of population genetics. **Population genetics** is the study of the allelic, genotypic, and phenotypic variation in a population. It tells us something about how populations are evolving and can help us make predictions about what's driving evolution.

The **Hardy-Weinberg equilibrium** gives us a tool to observe how populations evolve (or don't). It states that the frequencies of alleles and genotypes will stay the same through the generations as long as there are no evolutionary influences. In other words, our beetles will stay 86% green over time as long as the following requirements are met:

- Mating must be random
- Population size must be large, so one individual isn't accounting for a significant portion of the gene pool
- No migration, meaning individuals can't be entering or leaving the population
- No random mutations in the genes being studied
- No natural selection on the genes being studied

As long as our beetles follow these tenets, they will be in a Hardy-Weinberg equilibrium. You can imagine that on our unpredictable planet this kind of stability isn't the norm. So what good is this concept? Well, it gives us a sort of baseline. If the population deviates from the equilibrium, we'll know something is up in terms of evolution.

The **Hardy-Weinberg equation** allows us to calculate and predict genotype frequencies in large populations satisfying the equilibrium requirements. The Hardy-Weinberg equation is:

For a gene with two possible alleles, *p* and *q* represent the allelic frequency. Since we're dealing with frequencies and probabilities, the equation adds up to 1.

Let's use a diagram to see how this equation works with our beetles. There are only two alleles controlling the green and brown phenotype: 'A,' the dominant green allele, and 'a,' the recessive brown allele. We have 1,000 beetles in our parent population: 360 are green with the genotype AA, 480 are green with the genotype Aa, and 160 are brown with the genotype aa. So we can calculate the frequency of each genotype by dividing the number of each genotype by 1,000, giving us 0.36, 0.48, and 0.16.

But what's the frequency of each allele? Remember, each genotype includes the two inherited alleles. For the AA and aa genotypes, every individual has two identical alleles, so the allelic frequency for those members can just be carried over from the genotype frequencies (0.36 and 0.16). For the Aa genotype, half the alleles will be A and half will be a, so we will split that frequency (0.48) in half for each allele and add it to the frequencies from our AA and aa individuals.

The frequency of 'A:' 0.24 + 0.36 = 0.6

The frequency of 'a:' 0.24 + 0.16 = 0.4

Now we can say that the frequency of 'A' is 0.6 and the frequency of 'a' is 0.4. If we randomly pick a beetle from our population, there is a 60% chance it carries an 'A' allele and a 40% chance it carries an 'a' allele.

The power of the Hardy-Weinberg equation comes when our population starts producing offspring. Now we can look at our offspring to see if the allele frequencies match the parent generation. We can use the Hardy-Weinberg equation to predict what our allele frequencies would be in the absence of evolutionary pressure on our allele of interest. Every mother and father in our parent generation has a 60% chance of passing on an 'A' allele (assigned as *p* in our equation) and a 40% chance of passing on an 'a' allele (assigned as *q* in our equation).

- The probability of getting an AA individual is the probability of 'A' (0.6) times the probability of 'A' (0.6), or
*p*squared. - The probability of getting an aa individual is the probability of 'a' (0.4) times the probability of 'a' (0.4), or
*q*squared. - For the Aa individuals, multiply the probability of 'A' (0.6) by the probability of 'a' (0.4), or
*p*times*q*. Multiply that by 2, since there are two options for obtaining this genotype, depending on which allele comes from Mom or Dad.

The frequency for each genotype in the offspring population exactly matches the genotype frequencies in the parent population. Not too exciting, huh? But remember, genotype frequencies only stay consistent if there are no evolutionary pressures on our allele. If there is an evolutionary agent, however, you get to put on your scientist hat and try to figure out what factor is driving the change.

An **evolutionary agent** is any force that alters the genetic structure of a population. Some examples of evolutionary agents include mate choice, genetic drift, and natural selection. **Mate choice** is when one sex starts to prefer certain traits in their mate. Like if the lady beetles in our population started to prefer the cute brown boy beetles instead of the green. We can then predict that over time the 'a' allele would become more frequent in our population.

**Genetic drift** is a random process that results in certain individuals and their alleles being lost from the population. This is unlikely in a large population, but it cannot be discounted. For example, if a disease killed a disproportionately large number of green beetles, we would notice a direct effect on our allele frequencies and those of subsequent generations. Finally, **natural selection** represents environmental changes that result in a selective advantage for one or more genotypes. If a bird species is able to see the green beetles on the bark of trees better, the green beetles will often not survive long enough to reproduce. Therefore, the brown beetles will pass on their alleles more frequently.

**Hardy-Weinberg equilibrium** tells us that allelic frequencies will stay the same given no evolutionary agents. The **Hardy-Weinberg equation** allows us to calculate and predict genotype frequencies in large populations. This equation is only valid when a population satisfies the equilibrium requirement: random mating, a large population size, no migration, no random mutations, and no natural selection. We can use the equation to predict what allele frequencies will be over generations. If we observe deviations from those predicted frequencies, that clues us in that evolution is happening and we can go in search of the **evolutionary agents**, which are any force that alters the genetic structure of a population, influencing our gene. Evolutionary agents include **mate choice**, which is when one sex starts to prefer certain traits in their mate; **genetic drift**, which is a random process that results in certain individuals and their alleles being lost from the population; and **natural selection**, which represents environmental changes that result in a selective advantage for one or more genotypes.

To unlock this lesson you must be a Study.com Member.

Create your account

Are you a student or a teacher?

Already a member? Log In

BackWhat teachers are saying about Study.com

Already registered? Log in here for access

Did you know… We have over 160 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

You are viewing lesson
Lesson
2 in chapter 20 of the course:

Back To Course

TExES Life Science 7-12 (238): Practice & Study Guide32 chapters | 254 lessons | 28 flashcard sets

- SIE Exam Study Guide
- Indiana Real Estate Broker Exam Study Guide
- Grammar & Sentence Structure Lesson Plans
- Foundations of Science Lesson Plans
- Career, Life, & Technical Skills Lesson Plans
- Business Costs, Taxes & Inventory Valuations
- Using Math for Financial Analysis
- Assessments in Health Education Programs
- Governmental Health Regulations
- Understanding Health Education Programs
- AFOQT Prep Product Comparison
- ACT Prep Product Comparison
- CGAP Prep Product Comparison
- CPCE Prep Product Comparison
- CCXP Prep Product Comparison
- CNE Prep Product Comparison
- IAAP CAP Prep Product Comparison

- Curt Lemon in The Things They Carried
- Religion in Jane Eyre: Analysis & Examples
- Intrapreneurship in the Hospitality Industry
- Saadat Hasan Manto: Biography & Works
- Looking for Alaska Discussion Questions
- Indiana Real Estate Recovery Fund: Purpose & Claim Process
- Indiana Real Estate Brokers: Duties & Responsibilities
- Quiz & Worksheet - Achievements of President Jackson
- Quiz & Worksheet - State & Federal Rights in the Civil War
- Quiz & Worksheet - Agile Environments
- Quiz & Worksheet - Assessing Nutritional & GI Status
- Analytical & Non-Euclidean Geometry Flashcards
- Flashcards - Measurement & Experimental Design
- Kindergarten Math Worksheets & Printables
- Guided Reading Lesson Plans

- Western Civilization Study Guide
- FTCE Biology Grades 6-12 (002): Practice & Study Guide
- American Revolution Study Guide
- UExcel Contemporary Mathematics: Study Guide & Test Prep
- Holt McDougal Modern Biology: Online Textbook Help
- ILTS Mathematics: Spatial Visualization
- MTLE Earth & Space Science: Climate
- Quiz & Worksheet - Features of Company Mission Statements
- Quiz & Worksheet - Issues in Contemporary U.S. Policing
- Quiz & Worksheet - A Constitution's Impact on Government
- Quiz & Worksheet - Risk Assessment Methods
- Quiz & Worksheet - Power of a Quotient Property

- Organic Molecules: Functional Groups, Monomers & Polymers
- Hurricane Katrina: Facts, Timeline, Damage & Aftermath
- Common Core Standards in Delaware
- How to Calculate College GPA
- Illinois Common Core Social Studies Standards
- How Many Questions are on the TABE Test?
- Illinois Common Core Social Studies Standards
- Money Games for Kids
- Critical Thinking Games for Kids
- Columbus Day Activities for Kids
- Science Fiction Picture Books
- Common Core Standards in Rhode Island (RI)

- Tech and Engineering - Videos
- Tech and Engineering - Quizzes
- Tech and Engineering - Questions & Answers

Browse by subject