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.
US Airways, owned by the America Airlines Group operates a network of 193 destinations in 24 countries in North America, South America, Europe and the Middle East. It operates 3,028 daily flights including the US Airways Shuttle which provides an hourly service between Boston, New York City and Washington D.C. 10.