Why a single ovum is produced by oogenesis

The other ova become polar bodies.

Explanation: After meiosis I and II in oogenesis, there should be 4 eggs, but there aren't because the other eggs 3 eggs become these small cells called polar bodies that end up dying out through apoptosis. The reason why polar bodies are made is because they take out extra DNA that the single ovum is supposed to have.

So only 1 egg is made and the rest are polar bodies that get rid of extra DNA and then die by apoptosis.

where is the diagram?

if you insert the diagram ill be able to you

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.