AP Biology 5.4 Non-Mendelian Genetics

Elevated levels of $\mathrm{CO}_{2}$ increase the rate of photosynthesis and growth in plants. Scientists studying the mechanisms involved in these increases examined a variety of species and found that when plants are exposed to elevated levels of $\mathrm{CO}_{2}$, there is an increase in the number of chloroplasts per cell. To investigate whether the elevated levels of $\mathrm{CO}_{2}$ have a similar effect on the number of mitochondria in plant cells, the scientists then selected six of these species to quantify the number of mitochondria per cell when the plants were exposed to both normal and elevated levels of $\mathrm{CO}_{2}$ (Table 1).

The leaves of a particular plant species are typically green, but scientists notice a plant in which the leaves have white stripes. They determine that the stripes result from a mutation in mitochondrial DNA that interferes with the development of chloroplasts. The scientists crossed plants using pollen from the plant with white-striped leaves and ovules from a plant with green leaves. Predict the phenotype(s) of the leaves of offspring produced from this cross. Provide reasoning to justify your prediction. Explain why plants with the same genotype are able to differ in the structure and/or number of certain organelles in response to changes in atmospheric levels of $\mathrm{CO}_{2}$.

Write your responses to this question only on the designated pages in the separate Free Response booklet.