Show calculations in the blue booklet if more room is needed. AaDdNn was test cr
ID: 173003 • Letter: S
Question
Show calculations in the blue booklet if more room is needed. AaDdNn was test crossed with aaddnn. An earlier two-point cross suggested genes 'd' are 'n' were 15 cM apart. Complete the chart for the three-point test cross shown below are then answer the following questions (You are expected to rearrange the data if needed.) a.) Are these genes linked or on separate chromosomes? b.) If the genes were completely linked, what would be the expected numbers of DCOs? c.) If the genes assorted independently, what would be the expected numbers of each phenotype? d.) What gene is the middle gene? e.) Do these results agree with the findings from the earlier two-point test cross?Explanation / Answer
1. From the above data
the parental combinations are: n+a+d+=302 single cross1 between (n-a) : n+a-d- =55, and n-a+d+ = 50
n-a-d- = 293 single cross 2between (a-d) n+a+d- =131, and n-a-d+ = 124
Double cross-over n-a-d+ =21
(non-parentals) n+a+d- =24
From the above the gene "a" flips to give double cross, so gene 'a' is in the middle. The correct order the gene is n+a+d+/n-a-d-.
R.F between (n-a) = single cross1 + double cross/1000*100 = 55+50+21+24/1000*100 = 15cM
R F between (a-d) = single cross2 + double cross/1000*100 = 131+124+21+24/1000*100 = 30cM
R F between (n-d) = single cross1 + single cross2 + 2* Double cross/1000*100
= 55+50+131+124+2*90/1000*100 = 45cM
The order of gens is n-----------------a----------------------------------d
15cM 30cM =45cM
With two-point test cross the data does not agree. Because distance between d-a is 30cM but according three-point test cross the distance is 45cM.
The distance between genes are more so there is chance of link between the genes. So they are closely linked.