Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

6. Chromosomal Variation

Chromosomal Rearrangements: Inversions

Genetics

6. Chromosomal Variation

Chromosomal Rearrangements: Inversions

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1:11 minutes

Problem 11

Textbook Question

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

Verified step by step guidance

Step 1: Understand the difference between paracentric and pericentric inversions. A paracentric inversion occurs when the inverted segment does not include the centromere, while a pericentric inversion includes the centromere within the inverted segment.

Step 2: Analyze the image provided. The illustration shows a chromosomal inversion where segments of the chromosome are rearranged. In the case of crossing over within a paracentric inversion, the resulting gametes may include acentric fragments (lacking a centromere) and dicentric chromosomes (with two centromeres), which are often non-viable.

Step 3: For crossing over within a pericentric inversion, the inversion includes the centromere. The recombination results in gametes with duplications and deletions of genetic material, but these gametes retain centromeres, making them potentially viable but genetically imbalanced.

Step 4: Compare the genetic composition of gametes. In paracentric inversions, crossing over leads to structural abnormalities (acentric and dicentric chromosomes), whereas in pericentric inversions, crossing over results in genetic imbalances due to duplications and deletions.

Step 5: Conclude that the type of inversion (paracentric vs. pericentric) significantly impacts the viability and genetic composition of gametes derived from crossing over events within inversion heterozygotes.

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Key Concepts

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

Tetrads and Crossing Over

Tetrads are structures formed during meiosis when homologous chromosomes pair up. Crossing over occurs when segments of DNA are exchanged between these paired chromosomes, leading to genetic recombination. This process increases genetic diversity in gametes, which is crucial for evolution and adaptation.

Paracentric Inversion

Paracentric inversion is a chromosomal rearrangement where a segment of a chromosome is inverted, but the inversion does not include the centromere. When crossing over occurs in paracentric inversions, it can lead to the formation of acentric fragments, which can result in gametes with missing genetic information, affecting viability.

Pericentric Inversion

Pericentric inversion involves the inversion of a chromosome segment that includes the centromere. During crossing over in pericentric inversions, the resulting gametes can have duplications and deletions of genetic material. This can lead to viable but genetically unbalanced offspring, impacting traits and fitness.

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Related Practice

Multiple Choice

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after an paracentric inversion?

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after a pericentric inversion?

From the following list, identify the types of chromosome changes you expect to show phenotypic consequences.

Pericentric inversion

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Textbook Question

Inversions are said to 'suppress crossing over.' Is this terminology technically correct? If not, restate the description accurately.

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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.

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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 F and G. Identify the gametes that are formed following this crossover, and indicate which, if any, gametes are viable.

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Textbook Question

The outcome of a single crossover between nonsister chromatids in the inversion loop of an inversion heterozygote varies depending on whether the inversion is of the paracentric or pericentric type. What differences are expected?

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Textbook Question

A couple planning their family are aware that through the past three generations on the husband's side a substantial number of stillbirths have occurred and several malformed babies were born who died early in childhood. The wife has studied genetics and urges her husband to visit a genetic counseling clinic, where a complete karyotype-banding analysis is performed. Although the tests show that he has a normal complement of 46 chromosomes, banding analysis reveals that one member of the chromosome 1 pair (in group A) contains an inversion covering 70 percent of its length. The homolog of chromosome 1 and all other chromosomes show the normal banding sequence. Would you advise the woman that she will have to bring each pregnancy to term to determine whether the fetus is normal? If not, what else can you suggest?

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