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: Translocations

Genetics

6. Chromosomal Variation

Chromosomal Rearrangements: Translocations

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3:42 minutes

Problem 15a

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.

Verified step by step guidance

Understand the problem: A paracentric inversion is a type of chromosomal rearrangement where a segment of a chromosome is inverted but does not include the centromere. Here, the normal chromosome and its homolog with the inversion are given. The task is to diagram their alignment during prophase I of meiosis.

Recall that during prophase I, homologous chromosomes pair up and align to form a synaptonemal complex. This pairing requires homologous regions to align, even if one chromosome has an inversion.

To align the inverted segment with the normal chromosome, the inverted chromosome must form a loop. This is called an inversion loop. The loop allows the inverted sequence to align with the corresponding sequence on the normal chromosome.

Diagram the alignment: Start by drawing the normal chromosome as a straight line with the sequence ABC • DEFGHIJK. Then, draw the homolog with the inversion as a straight line, but include a loop in the region where the inversion occurs (djihgfe). Ensure that the sequences align properly within the loop.

Label the diagram clearly: Mark the centromere (·) on both chromosomes, and indicate the inverted region on the homolog. This will help visualize how the chromosomes align during prophase I.

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Key Concepts

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

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that have the same genes at the same loci but may carry different alleles. During prophase I of meiosis, these chromosomes align closely to facilitate genetic recombination, which is crucial for genetic diversity.

Paracentric Inversion

A paracentric inversion is a chromosomal rearrangement where a segment of a chromosome is inverted but does not include the centromere. This can affect the alignment and pairing of homologous chromosomes during meiosis, potentially leading to complications in gamete formation and genetic variation.

Prophase I of Meiosis

Prophase I is the first stage of meiosis, where homologous chromosomes pair up and exchange genetic material through a process called crossing over. This stage is critical for ensuring proper segregation of chromosomes and increasing genetic diversity in the resulting gametes.

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Related Practice

Textbook Question

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

How many chromosomes do you expect to see in karyotypes of the parents?

746

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Textbook Question

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

Explain how this is possible.

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Textbook Question

A woman who sought genetic counseling is found to be heterozygous for a chromosomal rearrangement between the second and third chromosomes. Her chromosomes, compared to those in a normal karyotype, are diagrammed to the right. This woman is phenotypically normal. Does this surprise you? Why or why not? Under what circumstances might you expect a phenotypic effect of such a rearrangement?

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

Paracentric inversion

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Multiple Choice

Which type of chromosomal rearrangement occurs when part of a chromosome breaks off and attaches to a nonhomologous chromosome?

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Multiple Choice

Which of the following represents the chromosomal segregation into gametes after a reciprocal translocation caused by adjacent-1 segregation? N=Normal chromosome T = Tanslocated chromosome

Which of the following ways reciprocal translocated chromosomes are sorted produces viable gametes?