Mendelian Genetics, Probability, Pedigrees, and Chi-Square Statistics Published July 2012
Revised October 2013
www.BioInteractive.org Page 1 of 10
TEACHER MATERIALS
The Making of the Fittest:
Natural Selection in Humans
MENDELIAN GENETICS, PROBABILITY, PEDIGREES,
AND CHI-SQUARE STATISTICS
OVERVIEW
This classroom lesson uses the information presented in the short film
The Making of the Fittest: Natural Selection in
Humans (http://www.hhmi.org/biointeractive/making-fittest-natural-selection-humans) to take students through a series
of questions pertaining to the genetics of sickle cell disease and its relationship to malaria resistance. We divided the
questions into sections: “Mendelian Genetics and Probability,” “Pedigrees,” and “Chi-Square Statistics.” Within each
section, the questions sequentially move from a basic level to a more advanced level in order to develop the skills of the
students.
KEY CONCEPTS AND LEARNING OBJECTIVES
• Having two of the same alleles of a given gene means an individual is homozygous; if the alleles are not identical, then
the individual is heterozygous.
• The sickle cell allele arose as a random mutation in the hemoglobin gene.
• Individuals who are homozygous for the sickle cell allele have sickle cell disease; individuals who are homozygous for
the normal hemoglobin allele do not have sickle cell disease but can contract malaria.
• Individuals who are heterozygous for the sickle cell allele are protected against malaria but do not get sickle cell
disease. Heterozygous individuals have a mix of normal and abnormal hemoglobin molecules.
Students will be able to
• use Punnett squares to predict the frequencies of genotypes in the next generation based on the genotypes of the
parents;
• understand the rules of probability as they relate to genetics problems;
• analyze pedigrees to deduce genotypes, phenotypes, and probabilities; and
• use the chi-square statistical analysis test to determine the significance of genetics data.
CURRICULUM CONNECTIONS
HS-LS3-1, HS-LS3-2, HS-LS3-3, HS-LS4-2, HS-LS4-3, HS-LS4-4
LS1.A, LS2.A, LS3.A, LS3.B, LS4.B, LS4.C
ELA-Literacy.RST.9-10.7, ELA-Literacy.RST.11-12.4, ELA-Literacy.RST.11-12.7
Math.Content.HSS-IC.A.1, Math.Content.HSS-MD.B.6
1.A.2, 3.A.3, 3.C.1, 3.C.2, 4.C.1
Topic 1, 4.1, 4.3, 5.4, 10.2
KEY TERMS
chi-square statistical analysis, codominance, dominant, genotype, hemoglobin, heterozygous, homozygous, incomplete
dominance, independent assortment, malaria, Mendelian genetics, pedigree, phenotype, probability, recessive, red
blood cells, sickle cell anemia, sickle cell disease
TIME REQUIREMENTS
This lesson was designed to be completed within one to two 50-minute class periods if the chi-square statistics section is
not included; if the chi-square statistics section is included, additional time may be required depending on the pace and
background of the students.