A healthy couple with a history of three previous spontaneous abortions has just had a child with cri-du-chat syndrome, a disorder caused by a terminal deletion of chromosome 5. Their physician orders karyotype analysis of both parents and of the child. The karyotype results for chromosomes 5 and 12 are shown here. Why does this parent have a normal phenotype?
Table of contents
- 1. Introduction to Genetics42m
- 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: Deletions
Multiple Choice
In the context of chromosomal rearrangements, what is the most accurate description of what happens when a piece of DNA is missing from a chromosome?
A
A deletion occurs, removing one or more genes from the chromosome, which can change gene dosage and phenotype.
B
An inversion occurs, reversing the orientation of a chromosomal segment without changing the total amount of DNA.
C
A duplication occurs, producing an extra copy of a chromosomal segment and increasing gene dosage.
D
A balanced reciprocal translocation occurs, exchanging segments between nonhomologous chromosomes without net loss of DNA.
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Verified step by step guidance1
Step 1: Understand the concept of chromosomal rearrangements, which are structural changes in chromosomes that can affect the DNA sequence and gene content.
Step 2: Identify the specific type of rearrangement described by the loss of a DNA segment from a chromosome. This means a portion of the chromosome is missing, leading to fewer genes than normal.
Step 3: Recognize that when a piece of DNA is missing, this is called a deletion. Deletions remove one or more genes, which can alter gene dosage (the number of copies of a gene) and potentially affect the organism's phenotype.
Step 4: Differentiate deletions from other rearrangements: inversions reverse a segment without loss, duplications add extra copies, and balanced reciprocal translocations exchange segments without net loss of DNA.
Step 5: Conclude that the most accurate description for a missing piece of DNA is a deletion, as it directly involves the removal of genetic material and can have significant biological consequences.
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