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.
With the United States containing so many world-Â­famous tourist destinations and being home to three giants of the aviation industry (US Airlines, American Airways, and Delta Air Lines), it's no surprise that the country's airports rank among the busiest in the world, weaving a complex network of routes all over the globe.