A normal chromosome and its homolog carrying a paracentric inversion are shown here. The dot (·) represents the centromere.
Normal ABC • DEFGHIJK
Inversion abc • djihgfe
Assume a crossover takes place in the region between F and G. Identify the gametes that are formed following this crossover, and indicate which, if any, gametes are viable.

Question

A normal chromosome and its homolog carrying a paracentric inversion are shown here. The dot (·) represents the centromere.

Normal ABC • DEFGHIJK

Inversion abc • djihgfe

Assume a crossover takes place in the region between F and G. Identify the gametes that are formed following this crossover, and indicate which, if any, gametes are viable.

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together which of the following gametes is produced following a crossover between a normal chromosome and its homologue. Having a perent inversion. The answer options are a two viable gams each with a duplication and a deletion. Option B two viable gams, one with the duplication and one with the deletion. Option C two nonviable gams, one with the duplication and one with the deletion. And option D two nonviable gams both with duplication and deletion. Recall that in a paracentric inversion, a segment of chromosome is rotated 100 and 80 degrees. And the centromere is involved on the screen is a picture or drawing of a perry centric inversion. The normal chromosome is a blue line and has gene order ABC D. The centromere represented by a black dot is located between genes B and C. The inversion chromosome which is represented by a red line has gene order A CBD. So the inversion is involving genes B and C. Now this does involve the centromere as it is located between genes C and B on the inversion chromosome crossing over involving a per centric inversion is achieved by an inversion loop. And then then, and a drawing of that inversion loop is on the screen. In order to match the gene order of the normal chromosome in blue, the inversion chromosome in red has to create that loop. Now, this inversion loop results in some unique crossover products. And I am putting those products up on the screen now. So a drawing of those products is on the screen. Let's go ahead and review them. The first is a normal chromosome. The second and the third products are recombinant for the second product gene A is duplicated and gene D is deleted in the third product gene A is deleted and gene D is duplicated. So both recombinant products have a duplication and deletion. The fourth or final product is the inversion chromosome with the incorrect gene order. Now, of these four products, the normal and the inversion chromosome will go on to produce viable Gams as all the genetic information is present. However, in the recombinant products that both contain a duplication and deletion, which I am circling in orange. Both of these products have missing genetic information and this would result in nonviable gams. Therefore, the correct answer is option D two nonviable gams, both with duplication and deletion. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.

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Key Concepts

Chromosomal Inversion

Crossover and Recombination

Viable Gametes