Cystic fibrosis chromosome defect kn which number of chromosoem
Reading File
Finding Sources
Cystic fibrosis is caused by a defect on Chromosome 7 — specifically at locus 7q31.2 (the long arm of chromosome 7).
Key details:
| Feature | Detail |
|---|---|
| Chromosome | 7 (long arm, locus 7q31.2) |
| Gene affected | CFTR — Cystic Fibrosis Transmembrane Conductance Regulator |
| Inheritance | Autosomal recessive |
| Most common mutation | ΔF508 (deletion of phenylalanine at position 508) |
| Protein function | CFTR is a chloride/bicarbonate ion channel on epithelial cells |
The defective CFTR protein leads to abnormal chloride and bicarbonate transport, causing thick, viscous secretions in the lungs, pancreas, liver, and other organs.
Sources: Ganong's Review of Medical Physiology, Robbins Pathologic Basis of Disease
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Reading File
🧬 Topic: Mendelian Inheritance Patterns
(High-yield for medicine, genetics, and exams)
What Is It?
Inheritance patterns describe how traits and diseases are passed from parents to children. Gregor Mendel's work with peas gave us the foundation. There are 5 main patterns in humans.
The 5 Inheritance Patterns
1. ✅ Autosomal Dominant (AD)
- Only one defective copy of the gene is needed to cause disease
- Affects males and females equally
- Affected parent → 50% chance of passing to each child
- Examples: Huntington's disease, Marfan syndrome, Achondroplasia (dwarfism)
🔑 Key clue: Disease appears in every generation (vertical transmission)
2. ✅ Autosomal Recessive (AR)
- Two defective copies needed to cause disease
- Parents are often carriers (one bad copy, no symptoms)
- 25% chance child is affected if both parents are carriers
- Examples: Cystic fibrosis (CFTR, chr 7), Sickle cell disease, PKU, Tay-Sachs
🔑 Key clue: Parents appear normal but child is sick; common in consanguineous (related) families
3. ✅ X-Linked Recessive
- Gene is on the X chromosome
- Males (XY) are always affected if they carry one copy (only one X)
- Females (XX) are usually carriers (protected by second X)
- Examples: Hemophilia A & B, Duchenne Muscular Dystrophy, Color blindness, G6PD deficiency
🔑 Key clue: Males affected >> females; no father-to-son transmission (father gives Y to sons)
4. ✅ X-Linked Dominant
- One defective copy on X causes disease in both males and females
- Often lethal in males (so more females seen affected)
- Examples: Fragile X syndrome, Rett syndrome, Incontinentia pigmenti
🔑 Key clue: Affected father passes to all daughters but NO sons
5. ✅ Mitochondrial Inheritance
- Mitochondria have their own DNA
- Passed only through the mother (egg contains mitochondria; sperm does not)
- All children of an affected mother may be affected
- Examples: MELAS, Leber's hereditary optic neuropathy (LHON)
🔑 Key clue: Maternal only — father NEVER passes it on
Quick Comparison Table
| Pattern | Copies Needed | Sex Bias | Famous Disease |
|---|---|---|---|
| Autosomal Dominant | 1 | None | Huntington's |
| Autosomal Recessive | 2 | None | Cystic Fibrosis |
| X-Linked Recessive | 1 (in males) | Males >> Females | Hemophilia |
| X-Linked Dominant | 1 | Females > Males | Fragile X |
| Mitochondrial | Any | None (maternal only) | MELAS |
Memory Trick 🧠
"AR needs a PAIR — you need TWO bad copies to care" "AD — only ONE to be SAD" "X-linked recessive — boys bear the BRUNT" "Mito = MOM only"
Connect Back to Cystic Fibrosis
CF is Autosomal Recessive — both parents carry one silent CFTR mutation on chromosome 7. When two carriers have children, the odds are:
- 25% affected (two bad copies)
- 50% carrier (one bad copy, healthy)
- 25% completely normal
Want me to go deeper on any of these patterns, do a practice quiz, or move to a new topic?
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