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Chapter 8: Problem 11

Contrast the genetic composition of gametes derived from tetrads of inversion heterozygotes where crossing over occurs within a paracentric versus a pericentric inversion.

Short Answer

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Short Answer: Crossing over within both paracentric and pericentric inversions in inversion heterozygotes adversely affects the genetic composition of the resulting gametes. In paracentric inversions, unbalanced and likely inviable gametes are produced due to the formation of dicentric and acentric chromatids. In pericentric inversions, gametes with unbalanced gene dosage are formed due to the presence of chromosomes with gene duplications and deletions, potentially leading to genetic disorders or inviability.

Step by step solution

01

Understand inversion heterozygotes and inversions

Inversion heterozygotes are individuals carrying one copy of a normal chromosome and one copy with an inversion. Inversions are chromosomal mutations where a segment of the chromosome is reversed. There are two types of inversions: paracentric and pericentric inversions.
02

Describe paracentric inversion

In a paracentric inversion, the centromere is not included in the inverted segment. This means that both breakpoints of the inversion are on the same arm of the chromosome.
03

Describe pericentric inversion

In a pericentric inversion, the centromere is included within the inverted segment. The breakpoints for the inversion occur on different arms of the chromosome.
04

Understand crossing over within paracentric inversion

When crossing over occurs within a paracentric inversion in a heterozygote, a loop is formed by synapsis of inverted and non-inverted chromosomes, and reciprocal exchange may happen. After the exchange during prophase I of meiosis, two types of chromatids are formed: dicentric (two centromeres) and acentric (no centromere) chromatids. These chromatids will not be properly segregated during anaphase I of meiosis, leading to unbalanced gametes that most likely will not survive.
05

Understand crossing over within pericentric inversion

When crossing over occurs within a pericentric inversion in a heterozygote, a loop is also formed by synapsis of inverted and non-inverted chromosomes. However, after the exchange during prophase I of meiosis, chromosomes with duplications and deletions of certain genes are formed. The resulting gametes will have an unbalanced genetic composition, which may lead to genetic disorders or inviability.
06

Compare genetic composition of gametes from paracentric and pericentric inversion

In both cases, the genetic composition of gametes is affected by crossing over within inversions. For paracentric inversions, the formation of dicentric and acentric chromatids leads to unbalanced and most likely inviable gametes. For pericentric inversions, the formation of chromosomes with duplications and deletions of certain genes results in gametes with unbalanced gene dosage, which may lead to genetic disorders or inviability.

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Most popular questions from this chapter

Human adult hemoglobin is a tetramer containing two alpha \((\alpha)\) and two beta \((\beta)\) polypeptide chains. The \(\alpha\) gene cluster on chromosome 16 and the \(\beta\) gene cluster on chromosome 11 share amino acid similarities such that 61 of the amino acids of the \(\alpha\) -globin polypeptide (141 amino acids long) are shared in identical sequence with the \(\beta\) -globin polypeptide \((146\) amino acids long \() .\) How might one explain the existence of two polypeptides with partially shared function and structure on two different chromosomes?

The mutations called bobbed in Drosophila result from variable reductions (deletions) in the number of amplified genes coding for rRNA. Researchers trying to maintain bobbed stocks have often documented their tendency to revert to wild type in successive generations. Propose a mechanism based on meiotic recombination which could account for this reversion phenomenon. Why would wild-type flies become more prevalent in Drosophila cultures?

What are inversion heterozygotes? How can meiotic pairing occur in these organisms? What will be the consequence?

What are the possible consequences of genome and gene duplication in the evolutionary process?

What are the possible reasons behind translocations?
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