You have identified several recessive mutations on a chromosome. These mutations

Question

You have identified several recessive mutations on a chromosome. These mutations include eyeless, Dpy-1 and hairy. You have a female worm that is heterozygous for eyeless, hairy, and dpy-1 and testcross the animal (i.e., mate the het to an animal homozygous for eyeless, hairy, dpy-1. Among the 1000 F1 progeny from the testcross, the following phenotypes were observed: Dpy-1, eyeless, hairy 450 wild type 470 hairy, dpy-1 40 eyeless 40 eyeless, hairy 34 dpy-1 36 eyeless, dpy-1 4 hairy 6 a) What gene is in the middle? b) What is the order of genes on the chromosome and the map distances between the genes? c) Calculate the interference?

Explanation / Answer

Let's write the genotype for the given progeny with mutations and wildtype being:

h for hairy, H for wildtype

e for eyeless, E for wildtype

d for dpy-1, D for wildtype

Always remember that there are parental genotype which are the ones that are most frequently found. The DCO or double crossover gametes will be present in the lowest requency. Then we have two sets of SCO or single crossover. Using this information and the above symbols we will make a table for the genotypes and the number of offsprings belonging to that genotype.

Now for the given progeny the genotype, observed number of offsprings and the type of gamete will be:

Type of Gamete

a) To determine the gene in the middle we compare each parental and double crossover event. The uncommon gene will then be the gene that will be in the middle.

First Parental genotype- d e h

First Double crossover- d e H

In this case we can see that h is the uncommon gene

Now comparing the next parental genotype and double crossover

Second parental genotype - D E H

Second Double Crossover- D E h

In this case as well we can see that h is the uncommon gene. Hence the gene in the middle is h.

b) Now from the above part and the given table we can determine that the gene order is:

d h e

In order to calculate the distance between the given genes we will use the following formula:

SCO+ DCO/Total number of Offsprings * 100 = Distance between genes in map units

or we can write it as:

[100*((SCO+ DCO)Total number of offsprings)] = Distance between genes

Now using the above formula. The distance between d and h will be:

[100*((34+36+4+6)/1000)] = 8 map units or 8 cM.

In the same way the distance between h and e will be:

[100*((30+40+4+6)/1000)] =  8 map units or 8 cM.

Thus, the map distance between d and h is 8 cM and the map distance between h and e is 8 cM.

Genotype Observed No. of offsprings

Type of Gamete

d e h 450 Parental D E H 470 Parental d E h 30 SCO between genes h and e D e H 40 SCO between genes h and e D e h 34 SCO between genes d and h d E H 36 SCO between genes d and h d e H 4 Double Crossover D E h 6 Double Crossover Total 1000

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

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