The answer is 20. Duplicated chromosome has two sister chromatids, identical copies of the chromosome. These two chromatids are joined at the region called centromere. Therefore, one duplicated chromosome has one centromere and two sister chromatids. If there are 20 duplicated chromosomes in a cell, there will be 20 centromeres.
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Considered among the most revolutionary airliners, the Douglas DC-3 is the most produced airliner in history. First flying in 1935, it remains in active service today. Pictured on its maiden voyage in 1968, the Boeing 737 is the most produced jet airliner in history. An airliner is a type of aircraft for transporting passengers and air cargo. Such aircraft are most often operated by airlines.