A team of biology graduate students are performing research on epigenetics and chromosome inactivation. The goal is to silence all the genes on a chromosome at once. The team chooses to develop a model based on a known human gene that can accomplish this task in vivo. Which of the genes listed below would be a suitable model for their research?
Q72
A 4-year-old girl is brought to the emergency department after falling off a chair and injuring her right leg. During the past 2 years, she has had two long bone fractures. She is at the 5th percentile for height and 20th percentile for weight. Her right lower leg is diffusely erythematous. The patient withdraws and yells when her lower leg is touched. A photograph of her face is shown. An x-ray of the right lower leg shows a transverse mid-tibial fracture with diffusely decreased bone density. Which of the following is the most likely cause of this patient's symptoms?
Q73
An investigator is studying the effect of chromatin structure on gene regulation. The investigator isolates a class of proteins that compact DNA by serving as spools upon which DNA winds around. These proteins are most likely rich in which of the following compounds?
Q74
A 1-year-old boy brought in by his mother presents to his physician for a routine checkup. On examination, the child is happy and playful and meets normal cognitive development markers. However, the child’s arms and legs are not meeting development goals, while his head and torso are. The mother states that the boy gets this from his father. Which of the following is the mutation associated with this presentation?
Q75
An 11-year-old male with light purple eyes presents with gradual loss of bilateral visual acuity. Over the past several years, vision has worsened from 20/20 to 20/100 in both eyes. He also has mild nystagmus when focusing on objects such as when he is trying to do his homework. He is diagnosed with a disease affecting melanin production in the iris. If both of his parents are unaffected, which of the following represents the most likely probabilities that another male or female child from this family would be affected by this disorder?
Q76
A baby is delivered at 39 weeks without complications. Upon delivery, there are obvious craniofacial abnormalities, including micrognathia, cleft lip, and cleft palate. On further inspection, downward slanting eyes and malformed ears are seen. The child has an APGAR score of 9 and 9 at 1 and 5 minutes respectively. There are no signs of cyanosis or evidence of a heart murmur. Which of the following is the most likely underlying cause of this patient’s presentation at birth?
Q77
A previously healthy 42-year-old man comes to the emergency room with constipation and diffuse, worsening abdominal pain for 2 days. He has no history of major medical illness. His father died in a car accident at the age of 32 years, and his mother has type 2 diabetes mellitus. A diagnosis of bowel obstruction is suspected and he is taken to the operating room for exploratory laparotomy. A partial resection of the colon is performed. The gross appearance of the patient's colonic tissue is shown. Microscopic examination shows tubular, tubulovillous, and villous adenomas. Assuming the patient's partner is not a carrier of the condition, which of the following is the likelihood that this patient’s children will develop this condition?
Q78
Researchers are investigating oncogenes, specifically the KRAS gene that is associated with colon, lung, and pancreatic cancer. They have established that the gain-of-function mutation in this gene increases the chance of cancer development. They are also working to advance the research further to study tumor suppressor genes. Which of the genes below is considered a tumor suppressor gene?
Q79
An investigator is studying the incidence of sickle cell trait in African American infants. To identify the trait, polymerase chain reaction testing is performed on venous blood samples obtained from the infants. Which of the following is required for this laboratory technique?
Q80
A 16-year-old boy is brought to the emergency department after losing consciousness. He had no preceding chest pain or palpitations. His father has cataracts and had frontal balding in his twenties but has no history of cardiac disease. His paternal grandfather also had early-onset balding. His pulse is 43/min. Physical examination shows frontal hair loss, temporal muscle wasting, and testicular atrophy. Neurologic examination shows bilateral foot drop and weakness of the intrinsic hand muscles. An ECG shows bradycardia with third-degree atrioventricular block. The severity of this patient's symptoms compared to that of his father is most likely due to which of the following genetic properties?
Molecular Genetics US Medical PG Practice Questions and MCQs
Question 71: A team of biology graduate students are performing research on epigenetics and chromosome inactivation. The goal is to silence all the genes on a chromosome at once. The team chooses to develop a model based on a known human gene that can accomplish this task in vivo. Which of the genes listed below would be a suitable model for their research?
A. NF1
B. Hox
C. XIST (Correct Answer)
D. SRY
E. Hedgehog
Explanation: ***XIST***
- The **XIST gene** (X-inactive specific transcript) is a key player in **X-chromosome inactivation** in females, leading to the transcriptional silencing of one of the two X chromosomes.
- This gene produces a **long non-coding RNA** that coats and silences an entire chromosome, making it a perfect model for studying whole-chromosome gene silencing.
*NF1*
- The **NF1 gene** encodes neurofibromin, a tumor suppressor protein, and is associated with **neurofibromatosis type 1**.
- Its role is primarily in cell growth regulation, not in the large-scale silencing of an entire chromosome.
*Hox*
- **Hox genes** are a group of related genes that control the body plan of an embryo along the **anterior-posterior (head-tail) axis** during early developmental stages.
- While critical for development, they do not function in general chromosome silencing mechanisms.
*SRY*
- The **SRY gene** (sex-determining region Y) is responsible for initiating **male sex determination** in mammals.
- It triggers the development of testes but does not play a role in silencing entire chromosomes; its function is specific to sexual differentiation.
*Hedgehog*
- The **Hedgehog signaling pathway** is an important regulator of development, cell differentiation, and tissue patterning.
- It is involved in various cellular processes and diseases like cancer but does not have a role in the epigenetic silencing of an entire chromosome.
Question 72: A 4-year-old girl is brought to the emergency department after falling off a chair and injuring her right leg. During the past 2 years, she has had two long bone fractures. She is at the 5th percentile for height and 20th percentile for weight. Her right lower leg is diffusely erythematous. The patient withdraws and yells when her lower leg is touched. A photograph of her face is shown. An x-ray of the right lower leg shows a transverse mid-tibial fracture with diffusely decreased bone density. Which of the following is the most likely cause of this patient's symptoms?
A. Type 2 collagen defect
B. Type 1 collagen defect (Correct Answer)
C. Type 5 collagen defect
D. Type 4 collagen defect
E. Type 3 collagen defect
Explanation: **Type 1 collagen defect**
- The recurrent **long bone fractures** from minor trauma, **short stature** (5th percentile for height), and diffusely **decreased bone density** on X-ray are classic signs of **osteogenesis imperfecta (brittle bone disease)**.
- **Osteogenesis imperfecta** is primarily caused by mutations in genes encoding type I collagen (COL1A1 and COL1A2), which is essential for bone strength.
*Type 2 collagen defect*
- Defects in **type II collagen** are most commonly associated with **chondrodysplasias**, which primarily affect cartilage and bone development, leading to skeletal dysplasias like **achondrogenesis** and **spondyloepiphyseal dysplasia**.
- While these conditions involve skeletal abnormalities, the hallmark features of osteogenesis imperfecta (recurrent fractures, blue sclerae, dentinogenesis imperfecta) are not typical with isolated type II collagen defects.
*Type 5 collagen defect*
- Defects in **type V collagen** are associated with **Ehlers-Danlos syndrome, classical type**, which primarily involves **skin hyperextensibility**, joint hypermobility, and tissue fragility, but not typically severe recurrent fractures from minor trauma due to bone fragility.
- While bone fragility can occur in some Ehlers-Danlos types, it's not the primary feature, and the clinical picture does not align as strongly as with type I collagen defects.
*Type 4 collagen defect*
- Defects in **type IV collagen** are primarily associated with **Alport syndrome**, which affects the **glomerular basement membrane** of the kidneys, leading to **progressive renal disease**, hearing loss, and ocular abnormalities.
- It does not cause recurrent long bone fractures or diffuse decreased bone density as seen in this patient.
*Type 3 collagen defect*
- Defects in **type III collagen** are associated with **Ehlers-Danlos syndrome, vascular type**, which is characterized by fragile blood vessels and organs, leading to a high risk of arterial rupture and internal organ perforation.
- While it can involve some tissue fragility, it does not typically present with recurrent long bone fractures and decreased bone density as the primary symptom.
Question 73: An investigator is studying the effect of chromatin structure on gene regulation. The investigator isolates a class of proteins that compact DNA by serving as spools upon which DNA winds around. These proteins are most likely rich in which of the following compounds?
A. Phosphate
B. Disulfide-bonded cysteine
C. Lysine and arginine (Correct Answer)
D. Heparan sulfate
E. Proline and alanine
Explanation: ***Lysine and arginine***
- DNA is **negatively charged** due to its phosphate backbone. Proteins that compact DNA (like **histones**) must be **positively charged** to electrostatically interact with and bind to DNA.
- **Lysine** and **arginine** are positively charged amino acids that are abundant in histones, facilitating this interaction.
*Phosphate*
- **Phosphate** groups are negatively charged and are a major component of the **DNA backbone** itself, not the proteins that compact DNA.
- Proteins rich in phosphate would be negatively charged, which would inhibit DNA binding due to **electrostatic repulsion**.
*Disulfide-bonded cysteine*
- **Cysteine residues** can form disulfide bonds, which are important for maintaining the **tertiary and quaternary structure** of many proteins.
- However, disulfide bonds do not primarily contribute to the basicity or positive charge required for DNA binding; rather, they play a crucial role in protein **folding and stability**.
*Heparan sulfate*
- **Heparan sulfate** is a **glycosaminoglycan** that is negatively charged and found on cell surfaces and in the extracellular matrix.
- It plays roles in cell signaling and adhesion but is not a component of the core histone proteins that compact DNA.
*Proline and alanine*
- **Proline** and **alanine** are common amino acids, but they are **nonpolar** or **neutral** at physiological pH.
- They do not contribute a significant **positive charge** to proteins, which is essential for binding to the negatively charged DNA.
Question 74: A 1-year-old boy brought in by his mother presents to his physician for a routine checkup. On examination, the child is happy and playful and meets normal cognitive development markers. However, the child’s arms and legs are not meeting development goals, while his head and torso are. The mother states that the boy gets this from his father. Which of the following is the mutation associated with this presentation?
A. FBN1 gene mutation
B. GAA repeat
C. Deletion of DMD
D. Underactivation of FGFR3
E. Overactivation of FGFR3 (Correct Answer)
Explanation: ***Overactivation of FGFR3***
- This presentation describes **achondroplasia**, a form of dwarfism characterized by **shortened limbs** (micromelia) due to impaired endochondral ossification, with a relatively normal-sized trunk and head.
- Achondroplasia is caused by a **gain-of-function mutation** in the **fibroblast growth factor receptor 3 (FGFR3)** gene, leading to its overactivation and inhibition of chondrocyte proliferation.
*FBN1 gene mutation*
- A mutation in the **FBN1 gene** is associated with **Marfan syndrome**, which is characterized by disproportionately long limbs (arachnodactyly), not short limbs.
- Marfan syndrome also typically involves skeletal (pectus abnormalities), ocular (lens dislocation), and cardiovascular (aortic root dilation) manifestations, which are not described.
*GAA repeat*
- A **GAA trinucleotide repeat expansion** in the Frataxin gene causes **Friedreich's ataxia**, a neurodegenerative disorder.
- Its symptoms include progressive ataxia, dysarthria, and cardiomyopathy, which are entirely different from the skeletal disproportion described.
*Deletion of DMD*
- A deletion in the **DMD gene** causes **Duchenne muscular dystrophy**, an X-linked recessive disorder characterized by progressive muscle weakness and degeneration.
- This condition primarily affects muscle function and is not associated with disproportionate limb shortening as the primary developmental issue.
*Underactivation of FGFR3*
- **Underactivity** or loss of function of **FGFR3** would lead to effects opposite to achondroplasia, such as excessive bone growth or craniosynostosis syndromes, rather than limb shortening.
- The phenotype of achondroplasia is specifically due to the constant activation and inhibitory signaling of FGFR3 on cartilage growth.
Question 75: An 11-year-old male with light purple eyes presents with gradual loss of bilateral visual acuity. Over the past several years, vision has worsened from 20/20 to 20/100 in both eyes. He also has mild nystagmus when focusing on objects such as when he is trying to do his homework. He is diagnosed with a disease affecting melanin production in the iris. If both of his parents are unaffected, which of the following represents the most likely probabilities that another male or female child from this family would be affected by this disorder?
A. Male: 25% Female: 25%
B. Same as general population
C. Male: 50% Female: 50%
D. Male: 50% Female: 0% (Correct Answer)
E. Male: 100% Female: 0%
Explanation: ***Male: 50% Female: 0%***
- The symptoms (light purple eyes, gradual vision loss, nystagmus, defective melanin production) are characteristic of **ocular albinism**. This condition is typically **X-linked recessive**.
- If the patient's mother is a **carrier** (XAXa) and the father is unaffected (XAY), there is a **50% chance** that a male child will inherit the affected X chromosome (XaY) and thus be affected, and a **0% chance** for a female child to be affected if the father is unaffected (all female children would either be carriers XAXa or unaffected XAXA).
*Male: 25% Female: 25%*
- This probability pattern would typically suggest an **autosomal recessive** inheritance pattern, where both parents are carriers (Aa x Aa), and there is a 25% chance for any child to be affected regardless of sex.
- However, ocular albinism most commonly follows an X-linked recessive pattern, and the described clinical features (e.g., light purple eyes due to melanin defect in the iris) are highly suggestive of ocular albinism.
*Same as general population*
- This would only be true if the disorder was not genetic or if the parents' carrier status did not increase the risk for subsequent children.
- Given the heritable nature of albinism and the specific family history (parents unaffected, one affected child), the risk for subsequent children is significantly higher than the general population.
*Male: 50% Female: 50%*
- This pattern would occur in an **autosomal dominant** disorder with 100% penetrance, where one parent is affected (Aa x aa), or in some specific scenarios of X-linked inheritance if the father was affected and the mother was a carrier.
- Ocular albinism is X-linked recessive, not autosomal dominant, and the father is stated to be unaffected.
*Male: 100% Female: 0%*
- This genetic pattern is highly unlikely unless the mother was fully mosaic for the condition or an extremely rare and specialized inheritance pattern was at play.
- In a typical X-linked recessive inheritance with an unaffected father and a carrier mother, there is always a 50% chance for a male child to be unaffected.
Question 76: A baby is delivered at 39 weeks without complications. Upon delivery, there are obvious craniofacial abnormalities, including micrognathia, cleft lip, and cleft palate. On further inspection, downward slanting eyes and malformed ears are seen. The child has an APGAR score of 9 and 9 at 1 and 5 minutes respectively. There are no signs of cyanosis or evidence of a heart murmur. Which of the following is the most likely underlying cause of this patient’s presentation at birth?
A. Microdeletion at chromosome 22q11.2
B. Mutation in the TCOF1 gene (Correct Answer)
C. Retinoic acid use during gestation
D. Mutation of the SOX9 gene
E. Trisomy 18
Explanation: ***Mutation in the TCOF1 gene***
- This clinical presentation, characterized by craniofacial abnormalities such as **micrognathia**, **cleft lip/palate**, **downward-slanting palpebral fissures**, and **malformed ears**, is highly consistent with **Treacher Collins syndrome**.
- **Treacher Collins syndrome** is an autosomal dominant disorder usually caused by a **mutation in the TCOF1 gene**, which affects cranial neural crest cell development.
*Microdeletion at chromosome 22q11.2*
- This describes **DiGeorge syndrome** (also known as 22q11.2 deletion syndrome), which typically presents with **cardiac defects** (e.g., tetralogy of Fallot), **abnormal facies** (e.g., short palpebral fissures, bulbous nose), **thymic hypoplasia** (T-cell immunodeficiency), **cleft palate**, and **hypocalcemia**.
- While cleft palate is present, the absence of cardiac or immunodeficiency signs makes Treacher Collins syndrome a more likely fit given the specific constellation of craniofacial findings.
*Retinoic acid use during gestation*
- **Retinoic acid embryopathy** (isotretinoin teratogenicity) can cause a range of birth defects, including **craniofacial dysmorphism** (e.g., microtia, micrognathia), **cardiac malformations**, and **central nervous system abnormalities** (e.g., hydrocephalus).
- While some features overlap, the specific pattern of severe craniofacial abnormalities without mention of CNS or cardiac issues makes Treacher Collins syndrome a stronger diagnosis.
*Mutation of the SOX9 gene*
- A **mutation in the SOX9 gene** is associated with **Campomelic Dysplasia**, a severe skeletal dysplasia characterized by **bowing of long bones**, short stature, and **sex reversal** in XY individuals.
- Although it can present with some facial anomalies (e.g., flat face, micrognathia), the absence of skeletal bowing and the specific combination of craniofacial defects make another diagnosis more likely.
*Trisomy 18*
- **Trisomy 18** (Edwards syndrome) typically presents with severe **growth retardation**, **developmental delay**, **micrognathia**, **rocker-bottom feet**, **clenched hands with overlapping fingers**, and often serious **cardiac defects**.
- While micrognathia is present, the full spectrum of features for Trisomy 18 is not described, and the specific craniofacial abnormalities strongly point away from this diagnosis.
Question 77: A previously healthy 42-year-old man comes to the emergency room with constipation and diffuse, worsening abdominal pain for 2 days. He has no history of major medical illness. His father died in a car accident at the age of 32 years, and his mother has type 2 diabetes mellitus. A diagnosis of bowel obstruction is suspected and he is taken to the operating room for exploratory laparotomy. A partial resection of the colon is performed. The gross appearance of the patient's colonic tissue is shown. Microscopic examination shows tubular, tubulovillous, and villous adenomas. Assuming the patient's partner is not a carrier of the condition, which of the following is the likelihood that this patient’s children will develop this condition?
A. 50% (Correct Answer)
B. 25%
C. 100%
D. 0%
E. 75%
Explanation: ***50%***
- The image and clinical scenario are highly suggestive of **familial adenomatous polyposis (FAP)**, an autosomal dominant condition characterized by hundreds to thousands of colonic adenomas.
- Since FAP is an **autosomal dominant** disorder, an affected individual (heterozygous for the gene) has a **50% chance** of passing the mutated gene to each child, regardless of whether the partner is a carrier.
*25%*
- A 25% likelihood would be expected in **autosomal recessive inheritance** if both parents are carriers.
- FAP does not follow an autosomal recessive inheritance pattern; it is an **autosomal dominant** disease.
*100%*
- A 100% likelihood would occur only if the affected parent were **homozygous for the mutation** (extremely rare and typically lethal) or in certain non-Mendelian inheritance patterns.
- In typical FAP cases, the affected parent is heterozygous, resulting in a 50% chance of transmission to offspring, not 100%.
*0%*
- A 0% likelihood would imply that the condition is not hereditary or that the affected parent cannot transmit the disease, which is incorrect for FAP.
- FAP is a **hereditary condition** with a clear autosomal dominant inheritance pattern, so there is always a 50% risk of transmission per child.
*75%*
- A 75% likelihood does not correspond to any standard Mendelian inheritance pattern.
- This percentage does not fit the **autosomal dominant pattern** observed in FAP, which consistently shows 50% transmission risk per child.
Question 78: Researchers are investigating oncogenes, specifically the KRAS gene that is associated with colon, lung, and pancreatic cancer. They have established that the gain-of-function mutation in this gene increases the chance of cancer development. They are also working to advance the research further to study tumor suppressor genes. Which of the genes below is considered a tumor suppressor gene?
A. Her2/neu
B. BRAF
C. BCL-2
D. JAK2
E. Rb (Correct Answer)
Explanation: ***Rb***
- The **retinoblastoma (Rb)** gene is a classic example of a **tumor suppressor gene**. Its protein product, Rb, plays a critical role in regulating the **cell cycle** by preventing uncontrolled cell division.
- When **Rb is mutated or inactivated**, cells can divide without proper checks, leading to tumor formation, particularly in cases like retinoblastoma.
*Her2/neu*
- **Her2/neu** (also known as ERBB2) is an **oncogene** that encodes a receptor tyrosine kinase involved in cell growth and differentiation.
- Its overexpression or amplification is associated with certain cancers, notably **breast cancer**, but it is not a tumor suppressor.
*BRAF*
- **BRAF** is an **oncogene** that codes for a serine/threonine kinase involved in the RAS/MAPK signaling pathway, which regulates cell growth.
- **Gain-of-function mutations** in BRAF are frequently found in melanoma, thyroid cancer, and colorectal cancer, promoting uncontrolled cell proliferation.
*BCL-2*
- **BCL-2** is an **anti-apoptotic gene**, meaning it prevents programmed cell death. While its overexpression can contribute to cancer by allowing abnormal cells to survive, it is not classified as a tumor suppressor gene.
- Instead, BCL-2 is considered an **oncogene** because mutations or overexpression promote cell survival and inhibit apoptosis.
*JAK2*
- **JAK2** (Janus Kinase 2) is a **proto-oncogene** encoding a tyrosine kinase involved in cytokine receptor signaling, which regulates hematopoiesis.
- **Gain-of-function mutations**, such as JAK2 V617F, are frequently found in **myeloproliferative neoplasms** (e.g., polycythemia vera, essential thrombocythemia, myelofibrosis), leading to uncontrolled blood cell production.
Question 79: An investigator is studying the incidence of sickle cell trait in African American infants. To identify the trait, polymerase chain reaction testing is performed on venous blood samples obtained from the infants. Which of the following is required for this laboratory technique?
A. Single-stranded binding proteins
B. Ligation of Okazaki fragments
C. Primers complementary to target DNA sequences (Correct Answer)
D. Complete genome DNA sequence
E. RNA-dependent DNA polymerase
Explanation: ***Primers complementary to target DNA sequences***
- **Primers** are short, synthetic single-stranded DNA sequences that **bind specifically** to the flanking regions of the target DNA sequence to be amplified.
- In PCR, these primers define the **start and end points** of the DNA segment that will be copied, allowing for the exponential amplification of a specific region of interest.
*Single-stranded binding proteins*
- **Single-stranded binding proteins (SSBs)** are crucial in **DNA replication** to stabilize unwound single-stranded DNA and prevent re-annealing or degradation.
- They are generally **not required** in standard PCR as the DNA strands are separated by heat denaturation, and the rapid cooling in primer annealing prevents re-annealing of the entire template.
*Ligation of Okazaki fragments*
- **Okazaki fragments** are short DNA segments synthesized on the **lagging strand** during **DNA replication**.
- Their ligation by **DNA ligase** is a key step in DNA replication, but it is **not part of the PCR process**, which synthesizes DNA continuously from primers.
*Complete genome DNA sequence*
- While knowing the **complete genome sequence** of an organism would be helpful for understanding the entire genetic makeup, it is **not a prerequisite** for performing PCR.
- PCR only requires knowledge of the **short flanking sequences** where the primers will bind to amplify a specific gene or region.
*RNA-dependent DNA polymerase*
- **RNA-dependent DNA polymerase**, also known as **reverse transcriptase**, is used to synthesize DNA from an RNA template in **reverse transcription PCR (RT-PCR)**.
- While RT-PCR is a variant of PCR, standard PCR, as described for identifying a genetic trait in DNA, **does not require this enzyme**; instead, it uses a **DNA-dependent DNA polymerase** (e.g., Taq polymerase).
Question 80: A 16-year-old boy is brought to the emergency department after losing consciousness. He had no preceding chest pain or palpitations. His father has cataracts and had frontal balding in his twenties but has no history of cardiac disease. His paternal grandfather also had early-onset balding. His pulse is 43/min. Physical examination shows frontal hair loss, temporal muscle wasting, and testicular atrophy. Neurologic examination shows bilateral foot drop and weakness of the intrinsic hand muscles. An ECG shows bradycardia with third-degree atrioventricular block. The severity of this patient's symptoms compared to that of his father is most likely due to which of the following genetic properties?
A. Penetrance
B. Codominance
C. Anticipation (Correct Answer)
D. Loss of heterozygosity
E. Pleiotropy
Explanation: ***Anticipation***
- **Anticipation** describes a genetic phenomenon where the severity of a genetic disorder increases and/or the age of onset decreases in successive generations. This is typical of disorders caused by **trinucleotide repeat expansions**, such as myotonic dystrophy.
- The patient's severe symptoms (third-degree AV block, foot drop, muscle wasting) occurring at a young age, compared to his father's milder symptoms (cataracts, early balding) without cardiac disease, are a classic presentation of anticipation in **myotonic dystrophy type 1 (DM1)**.
*Penetrance*
- **Penetrance** refers to the proportion of individuals with a particular genotype that express the associated phenotype.
- While it explains whether or not a trait is expressed, it does not explain the increasing severity or earlier onset across generations.
*Codominance*
- **Codominance** occurs when two different alleles for a gene are both expressed, and both phenotypes are observable (e.g., AB blood type).
- This concept does not apply to the increasing severity or earlier onset of symptoms observed in this family.
*Loss of heterozygosity*
- **Loss of heterozygosity** is a genetic event where an individual inheriting one mutated allele for a tumor suppressor gene loses the normal allele, leading to disease (e.g., retinoblastoma).
- This mechanism primarily relates to tumor formation and is not relevant to the progressive worsening of symptoms across generations in the context of myotonic dystrophy.
*Pleiotropy*
- **Pleiotropy** refers to a single gene affecting multiple phenotypic traits (e.g., the FBN1 gene in Marfan syndrome affecting skeletal, ocular, and cardiovascular systems).
- While myotonic dystrophy exhibits pleiotropy (affecting multiple systems), pleiotropy itself does not explain the intergenerational increase in severity or decrease in age of onset, which is specifically attributed to anticipation.
