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Chapter 8: Problem 21

A chromosome initially has the following segments: $$\underline{\mathrm{AB} \cdot \mathrm{CDEFG}}$$ Draw the chromosome, identifying its segments, that would result from each of the following mutations. a. Tandem duplication of DEF b. Displaced duplication of DEF c. Deletion of \(\mathrm{FG}\) d. Paracentric inversion that includes DEFG e. Pericentric inversion of BCDE

Short Answer

Expert verified
Chromosomal changes: a. AB 路 CDEFDEF G; b. AB 路 CDEFGDEF; c. AB 路 CDE; d. AB 路 CGFED; e. AEDC 路 BFG.

Step by step solution

01

Understanding Chromosome Segments

The chromosome initially consists of segments: \(\underline{\mathrm{AB} \cdot \mathrm{CDEFG}}\). Each letter represents a different segment within the chromosome.
02

Tandem Duplication of DEF

For tandem duplication, the segment \(\mathrm{DEF}\) appears next to its original location. Thus the chromosome becomes \(\underline{\mathrm{AB} \cdot \mathrm{CDEF}\underline{DEF} \mathrm{G}}\).
03

Displaced Duplication of DEF

Displaced duplication means that the duplicated segment \(\mathrm{DEF}\) is not immediately adjacent to its original. If \(\mathrm{DEF}\) is displaced to the end, the chromosome becomes \(\underline{\mathrm{AB} \cdot \mathrm{CDEFGDEF}}\).
04

Deletion of FG

Deletion removes a segment from the chromosome. After deletion of \(\mathrm{FG}\), the chromosome becomes \(\underline{\mathrm{AB} \cdot \mathrm{CDE}}\).
05

Paracentric Inversion Including DEFG

In a paracentric inversion, a segment is inverted and flipped, but the centromere is not involved. Here, \(\mathrm{DEFG}\) is inverted, resulting in \(\underline{\mathrm{AB} \cdot \mathrm{CGFED}}\).
06

Pericentric Inversion of BCDE

In a pericentric inversion, a segment including the centromere is inverted. Assuming \(\mathrm{CDE}\) involves the centromere, after inversion, the chromosome becomes \(\underline{\mathrm{AEDC} \cdot \mathrm{BFG}}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Tandem Duplication
Tandem duplication is a type of chromosomal mutation where a segment of the chromosome is copied and inserted directly adjacent to the original segment. For example, if we consider a chromosome represented by the segments \(\mathrm{AB \cdot CDEFG}\), a tandem duplication involving the segment \(\mathrm{DEF}\) would result in the chromosome becoming \(\mathrm{AB \cdot CDEF\underline{DEF}G}\). This mutation means that the segment \(\mathrm{DEF}\) is repeated side by side, causing an extension of the chromosome length. Tandem duplications can have significant effects on an organism, depending on the gene functions within the duplicated segment.
  • Provides extra copies of genes, potentially leading to increased production of the gene products.
  • May lead to genetic disorders if the duplication disrupts a crucial regulatory region of the chromosome.
Displaced Duplication
Displaced duplication occurs when a segment of a chromosome is duplicated and the copy is inserted elsewhere within the same chromosome or even different chromosome, but not directly adjacent to the original. In the given example of \(\mathrm{AB \cdot CDEFG}\), if the segment \(\mathrm{DEF}\) is duplicated and displaced, it might result in a chromosome looking like \(\mathrm{AB \cdot CDEFGDEF}\). This kind of duplication introduces additional genetic material at a different location, which might lead to various structural and functional consequences.
  • Can alter gene expression if regulatory sequences are affected by the displacement.
  • May contribute to evolutionary changes over generations by modifying genetic content that could adapt more favorably to environmental conditions.
Paracentric Inversion
A paracentric inversion involves a segment of a chromosome being reversed, or inverted, without including the centromere. Importantly, only one arm of the chromosome is affected by this inversion. Given the sequence \(\mathrm{AB \cdot CDEFG}\), if we perform a paracentric inversion on \(\mathrm{DEFG}\), the sequence changes to \(\mathrm{AB \cdot CGFED}\). Such inversions can influence genetic stability and fertility since they can cause problems during meiosis when the chromosomes must align.
  • Results in regions of inversion loops during meiosis, potentially leading to gametes with deletions or duplications.
  • May suppress recombination in the inversion area, affecting genetic diversity.
Pericentric Inversion
A pericentric inversion is a chromosomal rearrangement that involves the inversion of a segment of the chromosome along with the centromere. In the initial sequence \(\mathrm{AB \cdot CDEFG}\), if \(\mathrm{BCDE}\) (assuming \(\mathrm{CDE}\) includes the centromere) undergoes a pericentric inversion, the chromosome becomes \(\mathrm{AEDC \cdot BFG}\). This type of inversion impacts both arms of the chromosome and can cause considerable genetic consequences.
  • Can lead to unbalanced gametes during meiosis, which may result in non-viable or defective offspring.
  • Alters the structure of chromosomes which might disrupt important genes if breakpoints involve coding regions.

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Most popular questions from this chapter

Junctional epidermolysis bullosa (JEB) is a severe skin disorder that results in blisters over the entire body. The disorder is caused by autosomal recessive mutations at any one of three loci that help to encode laminin \(5,\) a major component in the dermal-epidermal basement membrane. Leena Pulkkinen and colleagues described a male newborn who was born with JEB and died at 2 months of age (L. Pulkkinen et al. 1997. American Journal of Human Genetics \(61: 611-619\) ); the child had healthy, unrelated parents. Chromosome analysis revealed that the infant had 46 normal-appearing chromosomes. Analysis of DNA showed that his mother was heterozygous for a JEB-causing allele at the \(L A M B 3\) locus, which is on chromosome \(1 .\) The father had two normal alleles at this locus. DNA fingerprinting demonstrated that the male assumed to be the father had, in fact, conceived the child. a. Assuming that no new mutations occurred in this family, explain the presence of an autosomal recessive disease in the child when the mother is heterozygous and the father is homozygous normal. b. How might you go about proving your explanation? Assume that a number of genetic markers are available for each chromosome.

What is the difference between primary Down syndrome and familial Down syndrome? How does each type arise?

Explain why recombination is suppressed in individuals heterozygous for paracentric and pericentric inversions.

What is the difference between a paracentric and a pericentric inversion?

How do translocations in which no genetic information is lost or gained produce phenotypic effects?
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