The letters X and Y represent missing events. Which option correctly replaces the letters X and Y? In X, the homologous chromosomes separate, which increases genetic diversity because of Y.

1. X: anaphase I
Y: independent assortment
2. X: prophase II
Y: crossing-over
3. X: anaphase II
Y: nondisjunction
4. X: prophase I
Y: nondisjunction

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.

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