Much like a ball of yarn is made of strands of strings, this x- shaped structure is made of what?

The X-shaped structure is made of strands of DNA.

Explanation:

The chromosomes are thread-like structures located in the nucleus of each cell in the body. In a human cell, there are 23 pairs of chromosomes found in the nucleus. Each chromosome is made up of strands of DNA tightly coiled many times around proteins called histones which gives support to its structure.

The chromosomes are X-shaped and are observed only in a cell undergoing division by mitosis or meiosis. Each of these X-shaped chromosomes consists of two identical sister chromatids. The sister chromatids are connected to each other by a region of the chromosome called the centromere. The centromere are located around the depression point of the chromosome which divides the sister chromatids into two regions: long arm called the q arm and a shorter arm called the p arm. During mitosis, spindle fibers attach to this region, and they eventually pull the sister chromatids apart to form two separate chromosomes, one for each daughter cell.

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