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Module 6 Mendelian Genetics

Lesson 3.6.7

3.6.7 page 3

Reflect and Connect

 

The incredible effect of temperature on the gender of Gecko hatchings is experimental evidence that genes are affected by the environment. Apply your understanding of the concepts of this lesson to the following questions.

 

Diploma Connection

 

Answer the following questions from a previous Biology 30 Diploma Exam.

 

Use the following information to answer the next question.

 

Sickle cell anemia is an autosomal recessive genetic disorder. Because individuals affected by sickle cell anemia have defective hemoglobin proteins, their blood cannot transport oxygen properly. There appears to be a relationship between the incidence of malaria and sickle cell anemia. Individuals with sickle cell anemia and carriers of the sickle cell allele have some resistance to malaria. Malaria is caused by the parasite Plasmodium and is transmitted between humans by mosquitoes.

  1. If scientists are successful in significantly reducing or eliminating malaria, the best prediction for what will happen to the allele for sickle cell anemia in the population is that it will

    1. not be affected by the elimination of malaria
    2. increase as its selective advantage is increased
    3. be reduced as its selective advantage is decreased
    4. quickly disappear as its selective advantage is increased

Use the following information to answer the next question.

 

Melanin pigments range in colour from yellow to reddish-brown to black. The amount and the colour of melanin in the skin account for differences in human skin coloration.

 

Albinism is a genetic disorder that results in unpigmented skin and other tissues. About 1 in 20 000 humans has albinism. In humans, it can be caused by an autosomal recessive allele (a). Its dominant allele (A) results in normal pigmentation.

 

  1. The fact that exposure to sunlight increases melanin production in many humans and produces a tan demonstrates that

    1. some people have mutations that prevent melanin production
    2. the expression of some genes is influenced by the environment
    3. the environment causes mutations that increase the chance of survival
    4. the environment causes mutations that have no effect on the chance of survival

Use the following information to answer the next question.

 

Sickle cell anemia is caused by the sickle cell allele (HbS) of a gene that contributes to hemoglobin (Hb) production. The abnormal hemoglobin (hemoglobin-S) produced causes red blood cells to become deformed and block capillaries; tissue damage results. Affected individuals homozygous for the sickle cell gene rarely survive to reproductive age. Heterozygous individuals produce both normal hemoglobin and a small percentage of hemoglobin-S. These individuals are more resistant to malaria than individuals who are homozygous for the allele for normal hemoglobin (HbA). Their red blood cells are prone to sickling when there is a deficiency of oxygen.

  1. Which of the following conclusions can be drawn from all of the information provided on sickle cell anemia?

    1. The sickle cell gene will eventually disappear because of its interaction with malaria.
    2. Malaria causes heterozygous individuals to be less fertile than homozygous individuals.
    3. In Africa, sickle cell anemia will disappear since it is lethal in the homozygous condition.
    4. In Africa, carriers for sickle cell anemia have an advantage over homozygous individuals

      1. Lesson Summary

         

        During this lesson, you were to explore the following focusing question:

        • How does the environment affect the expression of genes?

        Through your research for the discussion post, and from your exploration of temperature and gecko hatchings, you should see that there can be a strong and dynamic influence by the environment on gene expression. This influence accounts for some of the variance in traits like height. Whether this environmental effect on the expression of genes is stronger than the very inheritance of those genes is still up for debate.