G1 and G2  DNA  molecules 
 
 

                           homologous pair  
 
Examine the figures above. The top figure shows a homologous pair of DNA molecules during  the G1 stage and how  they will appear during G2 stage after DNA synthesis. The lower figure shows the homologous pair of chromosomes after the G2 stage  with letters representing genes attached. Included in this figure are the letters (T, t and ) which represent genes (segments of DNA that control traits that are inheritable). Note, in this figure there are two different sets of genes located on a homologous pair of chromosomes ( T's and G's).  In this example let us use   "T" represents a gene that causes a plant to grow tall (normal) and "t" represents a gene that prevents normal growth (dwarf) in height. Note that the genes on homologous  pair of chromosomes  may be different (T and t) because the cell received one of each chromosome from each of its parents; however the genes on the chromatids formed by the parent DNA must be identical (TT or tt).  Write in your notes an explanation of the differences between  genes on homologous chromosomes and sister chromatids. 
 

13. Which of the following shows the correct gene sequence found on the homologous pair of chromosomes above during the G1 stage G2 stage. 
 

                               G1                                          G2 

        a)               Tt and gg                            TTtt   and gggg 
        b)               Tt and Gg                           TTtt   and GGgg 
        c)               Tt and Gg                           TTTT and gggg 

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