
Objective: Students reason backward from pedigree evidence to the underlying mode of transmission of rare traits, reinforcing the student’s understanding of genetic transmission.
Each problem presents a family pedigree displaying a rare trait and asks the student:
• to determine whether the trait is dominant or recessive.
• to determine whether the trait is autosomal or xlinked.
The problems include traits that are (a) recessive autosomal, (b) recessive xlinked, (c) recessive indeterminate linkage, (d) dominant autosomal, (e) dominant indeterminate linkage, or (f) indeterminate dominance and linkage. 


Objective: Students develop an understanding of transmission probabilities involving carriers of recessive traits.
Each problem presents a family pedigree displaying a rare recessive trait and asks the student:
• to determine the dominance and linkage of the trait;
• the probability that various unaffected family members is a carrier of the allele for the trait;
• the probability that an unobserved family member will be affected by the trait.
The problems include traits that are recessive autosomal or recessive xlinked. 


Objective: This lesson extends basic Mendelian transmission to two genes and gene interactions that result in epistasis.
Each problem describes three parents that are true breeding for a single phenotypic trait. Each trait is governed by two genes, which have two alleles. The student:
• performs three crosses on the parent strains along with intercrosses on the resulting F1 progeny;
• determines the genotypes of the three true breeding strains and the genotype and phenotype of
the fourth possible truebreeding strain;
• determines the genotypes of all the F1 and F2 progeny;
• draws an inference about how the two genes interact to determine the phenotype. 


Objective: Students reason about how crossovers in meiosis reveal the order and intergene distances on chromosomes.
In each problem, students analyze the offspring resulting from a test cross with an organism that is heterozygous for three genes. Students:
• classify offspring phenotypes (parental, singlecrossover, or doublecrossover)
• identify the middle gene in the parental genotype
• calculate the recombination frequencies between each pair of genes along with the distances in
centimorgans between the pairs of genes. 


Objective: Students analyze populations and determine whether they are in HardyWeinberg equilibrium.
Each problem presents three phenotype numbers for a trait that is determined by a single gene with a dominant and recessive allele. The student:
• calculates the underlying allele frequencies;
• calculates the observed and expected genotype frequencies;
• calculates a chisquare test comparing observed and expected numbers to determine if the population is in equilibrium. 


Objective: Students calculate the shortterm impact of genotype fitness scenarios and reason about the longterm consequences for the population.
Each problem presents the homozygous recessive frequency in a population and describes selection pressure(s) on one or more genotype classes. The student:
• calculates allele frequencies, remaining genotype frequencies, and surviving genotype numbers in the
current generation;
• calculates the allele frequencies, genotype frequencies, and surviving genotype numbers in the next generation;
• summarizes how the genotype frequencies are changing across these generations and why;
• then views a graph displaying genotype frequencies across tens of generations;
• describes the long term impact of the selection pressures on genotype frequencies. 


Objective: Students model the interactions among the four components of various systems that regulate transcription.
Each problem describes a system that regulates transcription of a gene. The student:
• completes a summary description of the system;
• indicates how the presence or absence of the effector affects synthesis in the normally functioning system;
• indicates the impact of mutations to the three constituent genes, and whether extrachromosomal wild
type copies of the gene restores normal function.
The problems cover positive and negative inducible regulation, and negative repressible regulation. 


Objective: Students design experiments to determine the functioning of a gene regulation system. Each problem presents three genes and two possible effectors in a regulatory system. The student designs experiments to :
• examine the effect of the two possible effectors on gene expression to determine the actual effector in the system and to determine whether the system is inducible or repressible;
•examine the impact of selectively knocking out one gene at a time, and the impact of substituting a plasmid functional copy of the gene, to determine whether this is a positive or negative regulatory system and to identify the role of each gene. 


Objective: Students reason about how two genes act together to create offspring phenotype categories for a single trait. This activity is intended to precede the Gene Interaction and Epistasis module. Some problems describe the genes’ function and the student:
• summarizes how the genes interact in words;
• indicates the phenotypes of the truebreeding genotypes;
• indicates the offspring genotypes and phenotypes that result from crossing two truebreeding strains and intercrossing the offspring;
• describes in words how the genes interact to determine each phenoytpe.
In other problems, students are given the results of crossing truebreeding strains and intercrossing the offspring. The student:
• summarizes how the genes appear to interact in words;
• indicates the phenotypes of the truebreeding genotypes;
• explains the F2 phenotypes, phenotype ratios, and genotypes in the cross and describes how the genes interact to determine each phenotype. 


Objective: Students are given the frequencies of unordered tetrad types resulting from a cross and determine whether two genes are linked to each other or to the centromere. If so, students calculate the corresponding map distance. The student:
• classifies the tetrad types;
• reasons about the quantitative relationships among the tetrad types;
• draws qualitative linkage conclusions about the genes;
• calculates map distance when possible



Objective: Students calculate the probability that a child will be affected by each of two rare traits. Each problem presents: (a) the mode of transmission of each trait (autosomal or Xlinked, dominant or recessive); (b) the frequency in the population of dominant traits and the carrier frequency of recessive traits; and (c) the phenotypes of each parent. The student:
• calculates the probability of inheriting an allele for each trait from each parent;
• the probability the child is affected by each trait;
• the probability the child is affected by both traits.

