1. Module 8

1.12. Lesson 3

Lesson 3

Module 8—Populations, Individuals, and Gene Pools

 

Lesson 3—Hardy-Weinberg Calculations

The photo shows a child with a nebulizer.

© Vyacheslav Osokin/9330657/Fotolia

 

Get Focused

 

Cystic fibrosis, or CF, is an inherited autosomal recessive disease where the body produces abnormally thick, sticky mucus in the lungs, leading to difficulty breathing, respiratory infections, and failure to grow and thrive. Thick mucus blocks the ducts of the pancreas so fat-digesting enzymes cannot reach the intestine, leading to poor weight gain and inability to absorb fat-soluble vitamins.

 

CF is caused by a mutant allele of the CFTR gene. Those with the disease have inherited two copies of the mutant allele, one from each parent. CF occurs once in every 2500 Caucasian births. In the past, victims of CF did not live long enough to reproduce. With intensive therapy, lung transplants, and medication, those with CF are now living long enough to have babies and pass on the CF allele. For people with CF, in 1969, the median age of survival in North America was 14 years; in 2005, it was 36 years. Although this is great news for people with CF and for their families, population geneticists are interested in what this means for the frequency of the CF allele and the incidence of the disease in future populations.

 

We know that one in 2500 Canadians are born with CF (are homozygous recessive) and one in 25 carry the gene (are heterozygous). It would be interesting to know what the frequency of the recessive CF allele is relative to the normal dominant allele. Can we calculate these frequencies? Furthermore, can we find out if these frequencies are changing with the improved survival of CF patients? The answer is found in the Hardy-Weinberg principle.

 

In this lesson the following focusing questions will be examined:

  • How can the Hardy-Weinberg equation, involving allele and genotype frequencies in populations, graphs, and population data, be used to study changes in population over time?

  • How do we analyze and interpret this data to make predictions and decisions about population management?

frequency: how common something is; usually expressed as a decimal percentage; e.g., an incidence of “2 in 5” gives the same information as a frequency of 0.4 or 40%


Hardy-Weinberg equation: an equation used to determine the frequency of genotypes: p2 + 2pq + q2 = 1, where p = frequency of the dominant allele and q = frequency of the recessive allele

 

If the frequency of genotypes is known, the equation can be used to work backwards to find the frequency of alleles in the gene pool.


 

Module 8: Lesson 3 Assignment

 

Download a copy of Module 8: Lesson 3 Assignment to your computer now. Part 2 of the assignment involves a study of the action of natural selection and the Hardy-Weinberg conditions. You will also do some eating, so you might want to read the assignment now to select your “materials” for the lab. You will receive further instructions on how to complete this assignment later in the lesson.

 

In addition to your lesson work, any summary notes, sample calculations, diagrams, charts, or tables should be stored in the course folder for your teacher’s feedback and as study notes to help you prepare for exams.

 

You must decide what to do with the questions that are not marked by the teacher. Remember that these questions provide you with the practice and feedback that you need to successfully complete this course. You should respond to all of the questions and place those answers in your course folder.

 

Remember 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.