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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1:15 minutes

Problem 22b

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. What can you predict about the probability of abnormality/normality of their future children?

Verified step by step guidance

Understand the genetic abnormality: The husband has a chromosomal inversion on one of his chromosome 1 homologs. This means a segment of the chromosome has been flipped in orientation, which can lead to complications during meiosis due to improper alignment and crossing over.

Explain the concept of inversion: Inversions are structural chromosomal abnormalities that can be classified as pericentric (involving the centromere) or paracentric (not involving the centromere). In this case, the problem does not specify the type, but the large size of the inversion (70% of the chromosome) increases the likelihood of complications.

Analyze meiosis and gamete formation: During meiosis, homologous chromosomes pair and exchange genetic material through crossing over. In individuals with an inversion, the inverted chromosome may form a loop to align with its normal homolog. Crossing over within the inverted region can produce unbalanced gametes, leading to zygotes with duplications or deletions of genetic material.

Predict the outcomes for offspring: The couple's children could inherit one of four types of gametes from the husband: (1) a normal chromosome 1, (2) the inverted chromosome 1, (3) a chromosome with a duplication and deletion due to crossing over within the inversion, or (4) another chromosome with a different duplication and deletion. Gametes with duplications and deletions often result in miscarriage or severe developmental abnormalities.

Estimate the probability of normality: The probability of having a normal child depends on the proportion of viable gametes. If crossing over occurs within the inversion, a significant fraction of gametes may be unbalanced. However, if no crossing over occurs, the child could inherit either the normal or inverted chromosome 1, which may not cause issues if the inversion is balanced. Genetic counseling and further analysis can provide more precise probabilities.

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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. This can disrupt gene function and may lead to abnormal phenotypes, especially if the inversion affects critical genes. In this case, the husband's chromosome 1 has a significant inversion, which could impact the genetic stability of gametes and increase the risk of abnormalities in offspring.

Karyotype Analysis

Karyotype analysis is a laboratory technique that examines the number and structure of chromosomes in an individual's cells. It helps identify chromosomal abnormalities, such as aneuploidy or structural changes like inversions. In this scenario, the normal karyotype of 46 chromosomes indicates no major numerical abnormalities, but the presence of an inversion on chromosome 1 raises concerns about potential genetic risks for future children.

Genetic Counseling

Genetic counseling is a process that provides individuals or couples with information about genetic conditions and the risks of inheritance. It is particularly important for families with a history of genetic disorders or abnormalities. In this case, the wife's suggestion to seek genetic counseling is crucial, as it can help them understand the implications of the husband's chromosomal inversion and assess the probability of having children with genetic abnormalities.

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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

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.

560

views

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?

446

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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?

380

views

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. How would you explain the high incidence of past stillbirths?

567

views

Textbook Question

In the tomato, Solanum esculentum, tall (D−)(D−) is dominant to dwarf (dd) plant height, smooth fruit (P−) is dominant to peach fruit (pp), and round fruit shape (O−) is dominant to oblate fruit shape (oo). These three genes are linked on chromosome 1 of tomato in the order dwarf–peach–oblate. There are 12 map units between dwarf and peach and 17 map units between peach and oblate. A trihybrid plant (DPO/dpo) is test-crossed to a plant that is homozygous recessive at the three loci (dpo/dpo). The accompanying table shows the progeny plants. Identify the mechanism responsible for the resulting data that do not agree with the established genetic map.

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Textbook Question

A pair of homologous chromosomes in Drosophila has the following content (single letters represent genes):

Chromosome 1RNMDHBGKWU

Chromosome 2RNMDHBDHBGKWU

How does the pairing diagrammed in part (b) differ from the pairing of chromosomes in an inversion heterozygote?

364

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Textbook Question

What roles have inversions and translocations played in the evolutionary process?

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