I am just highly confused about the gene order. I know that it can be found usin

Question

I am just highly confused about the gene order. I know that it can be found using the double recombinant cross overs (by switching the last gene with the mddle one)> However, in these types of questions, I just can't figure out the gene order. Everything else makes sense.

Thank you :)

Problem 51 Three recessive genes on chromosome 2 of Drosophila melanogaster are: welt cinnabar, and brown. The numbers of phenotypes from a trihybrid test cross are shown below: Wild type 265 welt ,cinnabar ,brown 239 brown 1557 welt,cinnabar 1509 cinnabar 859 welt brown 829 welt 2368 brown .cinnabar 2365 What is the gene order and map distance between the three genes and what is the percent interference?

Explanation / Answer

Answer:

To determine the gene order, we need the parental genotypes as well as the double crossover genotypes. The least frequent genotypes are the double-crossover genotypes.

These genotypes are:

+ + + and wlcnbr.

Parental genotypes:

wl + + and + br cn

We can determine the order of the genes by analyzing the parental genotypes and the double cross over genotypes. The position (location) of the allele which is different in the parentals and double cross overs is the middle allele.

Because a double crossover switches the gene in the middle with respect to the genetic markers on either side of it, we have, in principle, a way of determining the gene order.

In the example above, comparison of the two genotypes reveals that, wl (welt) undergoes a change in location during the cross over event.

So, gene order in the above example:

cn------ wl------- br

Related Questions

Navigate

• Browse (All)
• Browse I
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.