Duchenne muscular dystrophy (DMD; OMIM 310200) and Becker muscular dystrophy (BMD; OMIM 300376) are both X-linked recessive conditions that result from different mutations of the same gene, known as dystrophin, on the long arm of the chromosome. BMD and DMD are quite different clinically. DMD is a very severe disorder that first appears at a young age, progresses rapidly, and is often fatal in the late teens to 20s. BMD, on the other hand, is much milder. Often symptoms don't first appear until the 40s or 50s, the progression of the disease is slow, and fatalities due to BMD are infrequent. Go to https://www.ncbi.nlm.nih/omim and survey the information describing the gene mutations causing these two conditions. Discuss the information you find with a few others in a small group, and write a single summary explaining your findings.
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
2. Mendel's Laws of Inheritance
Sex-Linked Genes
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Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
Which sex is more likely to express a recessive X-linked genetic disorder?
A
Females
B
Both sexes equally
C
Males
D
Neither sex

1
Understand that X-linked genetic disorders are caused by mutations in genes located on the X chromosome.
Recall that females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
Since the disorder is recessive, a female must have two copies of the mutated gene (one on each X chromosome) to express the disorder, whereas a male only needs one copy (on his single X chromosome) to express it.
Recognize that because males have only one X chromosome, any recessive mutation on that chromosome will be expressed, making males more likely to show the disorder.
Conclude that males are more likely to express a recessive X-linked genetic disorder due to their single X chromosome, while females are typically carriers unless both X chromosomes carry the mutation.
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Sex-Linked Genes practice set
