AP Biology 6.6 Gene Expression and Cell Specialization
Practise AP Biology 6.6 questions by connecting regulatory DNA and differential gene expression with specialized cell functions and phenotype.
- Syllabus
- Effective Fall 2025
- Course
- AP Biology
Exam points
- explain how promoters, operators, enhancers and transcription factors initiate or repress transcription
- explain how signaling molecules and tissue-specific regulators produce differential gene expression
- connect differential expression with cell specialization, embryonic development and stem-cell potential
- predict how regulatory-region mutations or altered transcription-factor binding change phenotype and cancer risk
Covered syllabus points
6.6 Gene Expression and Cell Specialization question 1
Lactase is the enzyme needed to digest lactose, the sugar found in milk. Most mammals produce lactase when they are young but once nursing ends. In humans however, many people continue to produce lactase into adulthood and are referred to as lactase-persistent. Which of the following mutations is most likely to cause lactase persistence in humans?
Figure 1. The relative concentrations of both the cyclin and CDK components of MPF
A
A nucleotide substitution in the coding region of the lactase gene that interferes with the interaction between lactase and lactose
B
A mutation that turns off the expression of transcription factors that activate the expression of lactase
C
A mutation that increases the binding of transcription factors to the promoter of the lactase gene
D
The insertion of a single nucleotide into the lactase gene that results in the formation of a codon
6.6 Gene Expression and Cell Specialization question 2
Housekeeping genes encode proteins involved in universally important processes such as transcription, translation, and glycolysis. Because these genes appear to be expressed in all cells at constant levels, the expression of housekeeping genes is often used as a control when comparing how the expression of other genes varies under different conditions.
Researchers studying the effect of pesticides on declining bee populations wanted to determine whether the expression of four housekeeping genes (GAPDH, RPL32, RPS5, and TBP-AF) was in fact constant in bees across different variables. The researchers collected samples of mRNA for each of the four genes and compared how their expression varied across the developmental stage of the bee, the sex of the bee, and the cell type from which the sample was taken. The mRNA from the samples was reverse transcribed to produce DNA copies of each gene. PCR was then used to amplify the DNA, and the Cq value was determined. The Cq value is the number of PCR cycles needed to produce a specified number of DNA copies. A high Cq value for a sample indicates the gene was expressed at a low level.
To analyze whether any of the examined variables affected expression of the housekeeping genes, researchers examined the range of Cq values for each gene in response to each variable. Genes with a wide range of Cq values were determined to be affected by the variable, while genes with a narrow range of Cq values were determined to be unaffected by the variable.
Figure 1. The effect of developmental stage, sex, and cell type on the Cq value of four housekeeping genes
Explain how expression of a gene such as GAPDH can vary from one cell type to another within the same bee.
Write your responses to this question only on the designated pages in the separate Free Response booklet.
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