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.
The biggest airlines flying to United States: American Airlines flights to United States, Delta flights to United States, Southwest Airlines flights to United States. Regions in the USA - United States. Airlines flying to the USA - United States - by city.
For information about the fleet of American's regional operations, see American Eagle (airline brand). American Airlines primarily operates a mix of Airbus and Boeing (including McDonnell Douglas) narrow-body and wide-body aircraft, as well as one narrow-body type from Embraer. American is currently in the process of the largest fleet renewal in its history, with over 270 aircraft remaining on order from Airbus and Boeing.