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 over 1,800 flights a day, serving 159 cities across the USA, Canada, Mexico and the Caribbean, Envoy is considered to be the world's largest regional airline system. Envoy is an affiliate member of the Oneworld airline alliance. The name American Eagle Airlines was also used between April 1980 and April 1981 by an unrelated air charter service that suspended operations and filed bankruptcy before flying any scheduled operations.