Spindle microtubules that never attach to a chromosome are called:

1. The spindle contains several classes of microtubule with different jobs. 2. Some grip chromosomes at the kinetochore and some do not. 3. Spindle microtubules that do not engage the chromosomes are called polar microtubules. 4. They push against each other to elongate the cell instead. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 10 'Cell Reproduction', sections 10.1-10.5_