Student Exploration: Microevolution
Vocabulary: allele, cystic fibrosis, deleterious, dominant allele, fitness, genotype, heterozygote superiority, heterozygous, homozygous, incompletely dominant, malaria, predator, recessive allele, sickle cell anemia
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
Many people from warm regions carry an allele that provides resistance to malaria. Two copies of this allele, however, causes a deadly blood disorder called sickle cell anemia.
Suppose two parents are healthy carriers of the sickle-cell allele. The genotype of each parent is AS (A is the normal allele, and S is the sickle-cell allele).
How likely is it for a child of these parents to have sickle cell anemia (SS)?
Do you think the allele for sickle cell anemia would be common in regions where malaria did not exist? Explain why or why not.
If natural selection does not favor one trait over another, the frequencies of various alleles in a population will tend to be stable over long periods of time. But what happens when one allele confers an advantage or disadvantage to an individual? These scenarios and others can be explored with the Microevolution Gizmo™.
The feather color of the parrots in the Gizmo is controlled by two alleles, D and d. The D allele is incompletely dominant over d. What is the feather color of each parrot genotype?
The fitness of parrots is determined by how well they blend into the background trees. Set the Fitness of DD slider to 100% and the other fitness sliders to 60%.
Click Begin, and then click Predator. Which parrots were killed by predators? Light Green and Yelllow because they did not blend in with the tree.
Deleterious dominant alleles
Get the Gizmo ready:
Set the DD and dd sliders to 34%.
Introduction: A deleterious allele is one that significantly lowers the fitness of an individual. If the deleterious allele is a dominant allele (D), then both homozygousDD and heterozygous Dd individuals will be at a disadvantage.