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MCAT

Unit 2: Lesson 1

Foundation 1: Biomolecules

Neurofibromin mutations in mice populations

Problem

Neurofibromin is a protein encoded by the NF1 gene on chromosome 17. Under normal circumstances, neurofibromin acts as a tumor suppressor in nerve cells. Certain mutations in the NF1 gene result in dysfunction of neurofibromin. As a result individuals with these mutations have an increased risk of developing certain benign and malignant tumors.
Neurofibromatosis type 1 is a hereditary disease in humans that is caused by a mutation in the NF1 gene. The disease is inherited in a dominant pattern, and manifests itself in the form of skin hyperpigmentation and numerous neurofibromas, a type of benign cutaneous nerve sheath tumors. In rare cases a neurofibroma may turn into a malignant tumor called a malignant peripheral nerve sheath tumor (MPNST). This process is known as malignant transformation.
In order to study neurofibromatosis type 1, a mouse model of the disease has been developed. The phenotypic patterns of the disease in the model mice includes neurofibromas and MPNSTs.
A researcher is studying the rate of phenotypic expression of neurofibromatosis in mice with NF1 mutation. To complete her study, she creates a large population of mice by initially mating a healthy female mouse with a homozygous diseased male mouse. The initial set of offspring is known as the first filial (F1) generation. The following generations mate at random until the population reaches 10,000 mice. The results of the study are stratified between mice with and without the NF1 mutation. The variables included are the number of mice with neurofibromas and the number of mice with MPNSTs. The results of this study are recorded in Table 1.
Table 1: Results of phenotypic expression in mice with and without NF1 mutation
Total numberNumber of mice with neurofibromasNumber of mice with MPNSTs
Mice with NF1 mutation64006400320
Mice without NF1 mutation360052
If two mice from the F1 generation of the study were crossed, what percentage of their offspring would have neurofibromatosis type 1?
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