Module 8

Module 8—Populations, Individuals, and Gene Pools

 

Lesson 1: Hardy-Weinberg Principle—the Gene Pool

 

Get Focused

 

In Unit C you focused on how individuals inherit their genes. In Unit D you will focus on how each living organism is part of a functioning population.

 

The Old Order Amish are a human population that immigrated to the United States from Switzerland in the 1800s in an attempt to escape modern technology and culture. They live apart in closed rural colonies, reproducing within their own communities and living much the same as farmers did 100 years ago. The Amish are of interest to population geneticists because of the prevalence of Ellis-van Creveld syndrome, a homozygous recessive condition that results in polydactyly, or extra digits on the hands and/or feet. Polydactyly is much more common in the Old Order Amish than in any other human population.   

 

Unlike the extra finger or toe that can be clearly seen in polydactyly, most of the time it is difficult to see the slight variations that exist between members of a population. Similarly, if there were two alleles for a gene, a dominant and recessive allele, it would be difficult to determine which allele or which genotype is most common in the population because the recessive allele is hidden in heterozygotes. It would also be difficult to determine whether the frequency of one genotype is increasing or decreasing, and what that might mean for the population’s success and survival.

 

Population biologists track this information. By knowing the frequency of alleles, genotypes, and phenotypes in a population, biologists can determine how a population is changing. A biologist might look at frequencies and ask the following questions:

• Why are there more and more homozygous recessives and fewer individuals with the dominant phenotype?
  
  
• Does it mean the population is being pressured by disease or predators?
  
  
• Is the population evolving in response to climate change? Why is one allele increasing over the other? Why is the other allele disappearing?

The ability to quantitatively measure the composition of a gene pool is an important skill for a biologist.

 

In this lesson the following focusing questions will be examined:

•  How do biologists quantitatively describe the composition of a population’s gene pool?
  
  
• What are the five conditions of the Hardy-Weinberg principle that affect frequency of alleles in a population’s gene pool, resulting in microevolution?
  
  
• What happens when conditions of the Hardy-Weinberg principle are not met?

Module 8: Lesson 1 Assignment

 

Download a copy of the Module 8: Lesson 1 Assignment to your computer now. You will receive further instructions on how to complete this assignment later in the lesson.

 

The other questions in this lesson are not marked by the teacher; however, you should still answer these questions. The “Self-Check” and “Try This” questions are placed in this lesson to help you review important information and build key concepts that may be applied in future lessons.

 

After a discussion with your teacher, you must decide what to do with the questions that are not part of your assignment. For example, you may decide to submit to your teacher the responses to “Try This” questions that are not marked. You should record the answers to all of the questions in this lesson and place those answers in your course folder.

 

Remember that you also have the option of trying additional questions from the textbook for further practice. Consult with your teacher for the answers to these questions. The Key will also provide you with many Diploma-Exam-style multiple-choice, numerical-response, and written-response questions that will be an excellent review of the module. Practising your responses to these types of questions is good preparation for the Diploma Exam.

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