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.
United makes this list of the best airlines at #60 in the world and #4 in the United States. It's the largest airline in the world by number of destinations served, spanning Asia, Australia, Africa, Europe, and the Americas, and it offers some seriously budget-friendly fares from Chicago, Houston, and other convenient hubs.