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How do we know that specific mutant phenotypes are due to changes in chromosome number or structure?
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Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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TOC.tableOfContents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Klug10th EditionEssentials of GeneticsISBN: 9780135588789Non è quello che usi tu?Cambia libro di testo
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Klug 10th EditionCh. 6 - Chromosome Mutations: Variation in Number and ArrangementProblema 1a
Klug 10th EditionCh. 6 - Chromosome Mutations: Variation in Number and ArrangementProblema 1aCapitolo 6, Problema 1a
How do we know that the extra chromosome causing Down syndrome is usually maternal in origin?
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Understand that Down syndrome is caused by trisomy 21, meaning there is an extra copy of chromosome 21 in the affected individual.
Recognize that to determine the origin of the extra chromosome, scientists analyze genetic markers called polymorphisms or short tandem repeats (STRs) on chromosome 21 from the child and both parents.
Collect DNA samples from the child with Down syndrome and both parents, then perform genotyping to identify which alleles (versions of a gene) are present on chromosome 21 in each individual.
Compare the child's alleles on chromosome 21 to those of the parents to see whether the extra chromosome 21 came from the mother or the father by identifying which parent's alleles are duplicated.
Review population studies that show a higher frequency of maternal nondisjunction events (errors in chromosome separation during meiosis) leading to the extra chromosome 21, thus concluding that the extra chromosome is usually maternal in origin.
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Nondisjunction during Meiosis
Nondisjunction is the failure of chromosome pairs to separate properly during meiosis, leading to gametes with an abnormal number of chromosomes. In Down syndrome, nondisjunction typically results in an extra copy of chromosome 21. Studying when and how nondisjunction occurs helps determine the parental origin of the extra chromosome.
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09:06
Meiosis Steps
Parental Origin Analysis Using Genetic Markers
Genetic markers such as microsatellites or single nucleotide polymorphisms (SNPs) are used to trace the origin of chromosomes. By comparing the child's chromosome 21 markers with those of the mother and father, researchers can identify whether the extra chromosome came from the mother or father, revealing that most cases are maternal in origin.
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07:11Mapping with Markers
Maternal Age Effect
The risk of nondisjunction increases with maternal age, which correlates with the higher incidence of Down syndrome in children born to older mothers. This age-related increase supports the conclusion that the extra chromosome 21 usually originates from errors in the mother’s egg cells during meiosis.
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03:38Maternal Effect
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How do we know that the mutant Bar-eye phenotype in Drosophila is due to a duplicated gene region rather than to a change in the nucleotide sequence of a gene?
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