Please draw a map indicating the relative positions of Genes A, B, C and D based on the following dihybrid cross data:

Rf between (cM):

a and b = 6

a and c = 50

a and d = 27

b and c = 50

b and d = 21

c and d = 50

Question

Please draw a map indicating the relative positions of Genes A, B, C and D based on the following dihybrid cross data:

Rf between (cM):

a  and  b  =  6

a  and  c  =  50

a  and  d  =  27

b  and  c  =  50

b  and  d  =  21

c  and  d  =  50

BlackTom AI · Accepted Answer

First, restate what the question is asking and what the data represent in a clear way so we can reason about the mapping.
The task asks you to draw a map showing the relative positions of Genes A, B, C, and D based on the given recombination fractions (centiMorgans) between each pair. The data show RF values between all pairs: A–B = 6 cM, A–C = 50 cM, A–D = 27 cM, B–C = 50 cM, B–D = 21 cM, C–D = 50 cM. In other words, some pairs are very close (low RF) and others appear effectively unlinked (RF ≈ 50%). With this in mind, evaluate the two statements.

Option A: I understand this question and know how to answer it
This claim would be true if you can translate the RFs into a rough gene order. A logical way to approach it is:
- Interpret the smallest RF as indicating the closest genetic distance and likely adjacency. Here, A–B = 6 cM is the smallest, so A and B are very close on the same chromosome.
- Note the pairs with RF = 50 cM (A–C, B–C, C–D are all 50, and C–D is 50 while A–D is 27 and B–D is 21). A recombination fraction around 50% typically means independent assortment and no tight linkage; this helps to place C and D away from the AB block or on different segments with respect to certain pairings.
- Compare the remaining distances: A–D = 27 cM and B–D = 21 cM suggest D is closer to the AB block than C is, but not as close as A–B. This information supports a tentative order such as A–B being adjacent, with D near them and C being farther away or on a different region depending on the exact three-point map considerations.
- From a conceptual standpoint, you should be able to sketch a map where A and B are close, D is moderately close to that AB cluster, and C is far from the AB cluster (due to multiple 50 cM values), recognizing that 50 cM suggests near-random assortment.
If you can articulate this approach and produce a plausible order consistent with the given RFs, you are demonstrating understanding and the ability to answer.

Option B: I do NOT understand this question and do NOT know how to do it
This statement would be true if you could not extract the meaning of RF values or translate them into a gene order, or if you were unsure how to handle the pairs with RF ≈ 50%.
- Misinterpretation to avoid: RF ≈ 50% does not always mean the genes are completely unlinked in all cases; it often indicates independent assortment or very large distances, but in a three- or four-point cross, relative positioning still matters and can be inferred by comparing multiple pairwise RFs.
- A common error would be assuming all 50% values imply the genes are on separate chromosomes or that no information can be extracted at all. In fact, the pattern here provides a consistent arrangement: A and B are tightly linked (6 cM), with D closer to the AB bloc than C, which shows many 50 cM pairings that help place C away from the AB-D cluster.
- Another pitfall is attempting to force a too-precise three-point map without considering the limited data. The data permit a plausible ordering or at least a partial map, even if the exact linear arrangement requires more data or recombination events to resolve conclusively.

Summary of the distinctions:
- If you can outline a principled approach using the smallest RF to anchor A and B, use the moderate RFs to place D relative to that block, and interpret 50 cM values as indicating distance or separation for C, you are demonstrating understanding and can proceed to draw the map. This supports Option A.
- If you feel you cannot interpret these RF patterns or you think the data are insufficient to draw any map, you would be aligned with Option B, but that stance ignores the informative pattern (6, 27, 21) that guides a reasonable arrangement.

01:447:380:17 GENETICS Week 10- In Person problem set_Fa25

Please draw a map indicating the relative positions of Genes A, B, C and D based on the following dihybrid cross data: Rf between (cM): a and b = 6 a and c = 50 a and d = 27 b and c = 50 b and d = 21 c and d = 50

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