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.
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
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
6. Chromosomal Variation
Chromosomal Rearrangements: Translocations
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Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
Which of the following ways reciprocal translocated chromosomes are sorted produces viable gametes?
A
Adjacent-1 segregation
B
Adjacent-2 segregation
C
Alternative segregation

1
Understand the concept of reciprocal translocation: This occurs when two non-homologous chromosomes exchange segments, leading to a rearrangement of genetic material.
Learn about the different types of segregation patterns during meiosis in translocated chromosomes: Adjacent-1, Adjacent-2, and Alternative segregation.
Adjacent-1 segregation involves the separation of homologous centromeres, leading to gametes with duplications and deficiencies, which are typically inviable.
Adjacent-2 segregation involves the separation of non-homologous centromeres, also resulting in gametes with duplications and deficiencies, which are typically inviable.
Alternative segregation results in the separation of translocated chromosomes from their normal homologs, producing balanced gametes with no duplications or deficiencies, thus viable.
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Chromosomal Rearrangements: Translocations practice set
