Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

Example Input: Heme is critical for a variety of cellular processes, but excess intracellular heme may result in oxidative stress and membrane injury. Feline leukemia virus subgroup C receptor (FLVCR1), a member of the SLC49 family of four paralogous genes, is a cell surface heme exporter, essential for erythropoiesis and systemic iron homeostasis. Disruption of FLVCR1 function blocks development of erythroid progenitors, likely due to heme toxicity. Mutations of SLC49A1 encoding FLVCR1 are noted in patients with a rare neurodegenerative disorder: posterior column ataxia with retinitis pigmentosa. FLVCR2 is highly homologous to FLVCR1 and may function as a cellular heme importer. Mutations of SLC49A2 encoding FLVCR2 are observed in Fowler syndrome, a rare proliferative vascular disorder of the brain. The functions of the remaining members of the SLC49 family, MFSD7 and DIRC2 (encoded by the SLC49A3 and SLC49A4 genes), are unknown, although the latter is implicated in hereditary renal carcinomas. SLC48A1 (heme responsive gene-1, HRG-1), the sole member of the SLC48 family, is associated with the endosome and appears to transport heme from the endosome into the cytosol.
Example Output: Which SLC family is FLVCR1 a member of?

Example Input: The apolipoprotein E type 4 allele is a susceptibility gene for late-onset Alzheimer's disease. Apolipoprotein E is found in neurons, some of which contain paired helical filaments made of the microtubule-associated protein tau. Previous studies have demonstrated that the apoE3 isoform, but not the apoE4 isoform, binds tau with high avidity. Because the microtubule-associated protein MAP2c also effects microtubule assembly and stability, we examined interactions between apoE isoforms and MAP2c. Similar to the tau-binding results, apoE3, but not apoE4, bound MAP2c. Binding was detectable down to 10(-9) M MAP2c and 10(-8) M apoE3. Isoform-specific interactions of apoE with the microtubule-associated proteins MAP2c and tau might affect intracellular maintenance of microtubules and could contribute to a time-dependent pathogenesis of Alzheimer's disease.
Example Output: Which ApoE isoform is associated with atherosclerosis and Alzheimer's disease?

Example Input: The genetic information of the cell, or DNA, is stored in the nucleus. During mitosis, two nuclei (plural for nucleus) must form, so that one nucleus can be in each of the new cells after the cell divides. In order to create two genetically identical nuclei, DNA inside of the nucleus must be copied or replicated. This occurs during the S phase of the cell cycle. During mitosis, the copied DNA is divided into two complete sets, so that after cytokinesis, each cell has a complete set of genetic instructions. To begin mitosis, the DNA in the nucleus wraps around proteins to form chromosomes. Each organism has a unique number of chromosomes. In human cells, our DNA is divided up into 23 pairs of chromosomes. Replicated DNA forms a chromosome made from two identical sister chromatids, forming an "X" shaped molecule ( Figure 1.1). The two chromatids are held together on the chromosome by the centromere. The centromere is also where spindle fiber microtubules attach during mitosis. The spindles separate sister chromatids from each other. During mitosis, the two sister chromatids must be divided. This is a precise process that has four individual phases to it. After the sister chromatids separate, each separate chromatid is now known as a chromosome. Each resulting chromosome is made of DNA from just one chromatid. So, each chromosome after this separation is made of "1/2 of the X." Through this process, each daughter cell receives one copy of each chromosome. The four phases of mitosis are prophase, metaphase, anaphase and telophase ( Figure 1.2). 1. Prophase: The chromatin, which is unwound DNA, condenses forming chromosomes. The DNA becomes so tightly wound that you can see them under a microscope. The membrane around the nucleus, called the nuclear envelope, disappears. Spindles also form and attach to chromosomes to help them move. 2. Metaphase: The chromosomes line up in the center, or the equator, of the cell. The chromosomes line up in a row, one on top of the next. 3. Anaphase: The two sister chromatids of each chromosome separate as the spindles pull the chromatids apart, resulting in two sets of identical chromosomes. 4. Telophase: The spindle dissolves and nuclear envelopes form around the chromosomes in both cells. An overview of the cell cycle and mito- sis: during prophase the chromosomes condense, during metaphase the chromo- somes line up, during anaphase the sister chromatids are pulled to opposite sides of the cell, and during telophase the nuclear envelope forms. This is a representation of dividing plant cells. Cell division in plant cells differs slightly from animal cells as a cell wall must form. Note that most of the cells are in interphase. Can you find examples of the different stages of mitosis?
Example Output:
what holds the two chromatids together?