Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization

Problem 15b

Chapter 10, Problem 15b

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.

Verified step by step guidance

Step 1: Understand the concept of a paracentric inversion. A paracentric inversion occurs when a segment of a chromosome is reversed, but the inversion does not include the centromere. In this problem, the inversion affects the region from D to J.

Step 2: Recognize the consequences of crossing over in the inverted region. When a crossover occurs between F and G in the inverted region, it can lead to the formation of a dicentric chromosome (with two centromeres) and an acentric fragment (without a centromere). These structures are typically non-viable.

Step 3: Analyze the gametes formed. After the crossover, the resulting chromatids will include: (1) a normal chromatid, (2) an inverted chromatid, (3) a dicentric chromatid, and (4) an acentric fragment. The dicentric and acentric products are usually lost during cell division due to their structural instability.

Step 4: Determine the viability of the gametes. The normal and inverted chromatids are viable because they retain a single centromere and complete genetic information. The dicentric and acentric products are non-viable due to their inability to segregate properly during meiosis.

Step 5: Summarize the outcome. The viable gametes are those carrying either the normal chromosome or the inverted chromosome. The gametes containing the dicentric chromosome or acentric fragment are non-viable.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chromosomal Inversion

A chromosomal inversion occurs when a segment of a chromosome is reversed end to end. In the case of a paracentric inversion, the inverted segment does not include the centromere. This structural alteration can affect gene expression and recombination during meiosis, particularly when crossovers occur within the inverted region.

Crossover and Recombination

Crossover is a genetic process during meiosis where homologous chromosomes exchange segments of genetic material. This event increases genetic diversity in gametes. However, in the presence of inversions, crossovers can lead to the formation of nonviable gametes due to the production of unbalanced chromosomal arrangements, which can result in lethal combinations.

Viable Gametes

Viable gametes are those that can successfully participate in fertilization and develop into a viable organism. In the context of inversions and crossovers, certain gametes may carry duplications or deletions of genetic material, rendering them nonviable. Identifying which gametes are viable requires analyzing the resulting chromosomal arrangements post-crossover.

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Gamete Development

Related Practice

Textbook 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

Diagram the alignment of chromosomes during prophase I.

Textbook 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 A and B. Identify the gametes that are formed by this crossover event, and indicate which, if any, gametes are viable.

Textbook Question

Dr. Ara B. Dopsis has an idea he thinks will be a boon to agriculture. He wants to create the 'pomato,' a hybrid between a tomato (Lycopersicon esculentum) that has 12 chromosomes and a potato (Solanum tuberosum) that has 48 chromosomes. Dr. Dopsis is hoping his new pomato will have tuber growth like a potato and the fruit production of a tomato. He joins a haploid gamete from each species to form a hybrid and then induces doubling of chromosome number.

How many chromosomes will the polyploid have after chromosome doubling?

Textbook Question

Can Dr. Dopsis be sure the polyploid will have the characteristics he wants? Why or why not?

Textbook Question

The accompanying chromosome diagram represents a eukaryotic chromosome prepared with Giemsa stain. Indicate the heterochromatic and euchromatic regions of the chromosome, and label the chromosome's centromeric and telomeric regions.

Do you expect the centromeric region to contain heterochromatin? Why or why not?

Textbook Question

What term best describes the shape of this chromosome?

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