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Examine the diagram above  showing one homologous pair of chromosomes as they would appear during prophase. Each chromosome consists of two chromatids held together by a centromere. The two chromatids bound together by a centromere are called sister chromatids.  In this figure one of the sister chromatids represent the parental DNA molecule which formed its sister chromatid during DNA replication (S stage). The letters R (upper case) r (lower case) represent two genes for the same trait. For example "R" represents a gene that produces red pigments in the flower of a red rose and "r" represents the gene that produces white pigments in the flower of a white roses. Note that genes of separate homologous do not need to be identical (r and R) but genes on the sister chromatids have to be identical (rr and RR) 
 
 
 
 
 
 

                      chromosomes  
 15. How many chromosomes are represented in this figure? 

       a) 2          b) 4        c) 8         d) 16 

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16. How many chromatids are represented in this figure? 

       a) 2           b) 4        c) 8        d) 16 

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17. How many centromeres are represented in this figure? 

       a) 2           b) 4        c) 8         d) 16 

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