During which stage of meiosis does crossing over usually occur?

a. prophase i

b. metaphase i

c. prophase ii

d. metaphase ii

A. Prophase l

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Explanation:

Prophase I of meiosis I is a process that involves five different stages during which genetic material in the form of alleles crosses over and recombines to form non-identical haploid chromatids. Prophase I is the first stage of meiosis I, followed by prophase II, anaphase I, anaphase II, metaphase I and metaphase II.

Prophase is the starting stage of cell division in eukaryotes. Prophase, in both mitosis and meiosis, is recognized by the condensing of chromosomes and separation of the centrioles in the centrosome. This organelle controls the microtubules in the cell, and each centriole is one half of the organelle. During prophase, they separate to provide microtubule centers in each new cell. Organelles, chromosomes, and many other substances and structures are moved about the cell by microtubules and associated proteins. These structures together are known as molecular motors and drive many cell processes. Prophase begins cell division by separating the centers for these molecular motors, and condensing the chromosomes.

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organisms that are both used in toothpaste as well as cause malaria are protista and monera.

the answer to your question is b