Single Gene Disorders: Terminology & Concept Recap – Medical Genetics | Lecturio

Summary

This lecture on single gene disorders explores their Mendelian inheritance patterns, emphasizing essential genetic terminology. It introduces concepts like locus, haplotype, and compound heterozygote, highlighting how mutations can arise from different genetic backgrounds. The discussion extends to pleiotropy, demonstrating how one gene can affect multiple traits, and differentiates between penetrance and expressivity, both crucial for genetic counseling. Understanding these factors is vital for predicting disease outcomes and managing familial genetic disorders.

Takeaways

• 😀 Single gene disorders follow Mendelian inheritance patterns.
• 📚 A recommended reference for understanding single gene disorders is 'Mendelian Inheritance in Man' by Victor McKusick.
• 🔍 The term 'locus' refers to the specific location of a gene on a chromosome.
• 🔄 A 'compound heterozygote' has two different mutant alleles from different backgrounds, appearing homozygous for a recessive condition.
• 🔬 Recessive alleles are generally uncommon, often having multiple mutations at a specific locus.
• 🌐 Pleiotropy indicates that one gene can have multiple effects on different traits.
• 📊 'Penetrance' refers to the percentage of individuals with a specific genotype that express the associated phenotype.
• 🌈 'Variable expressivity' means that individuals with the same genotype can exhibit different degrees of expression of the trait.
• 📉 Genetic counseling can be complicated by penetrance and expressivity, making outcome predictions challenging.
• 👨‍👩‍👧‍👦 Pedigrees are often used in genetic counseling to assess and predict genetic disorders within families.

Q & A

What are single gene disorders and how do they relate to Mendelian inheritance?

Single gene disorders are genetic conditions that result from mutations in a single gene and follow Mendelian inheritance patterns, which means they can be passed down through generations according to predictable ratios.

What is the significance of 'Mendelian Inheritance in Man' by Victor McKusick?

This book is a classic reference tool that lists all known single gene disorders and is recommended for future practice, providing essential information for understanding genetic conditions.

What does the term 'locus' refer to in genetics?

A locus refers to the specific physical location of a gene on a chromosome, where various genotypes can be identified.

What is a haplotype?

A haplotype is the combination of alleles at different loci that are inherited together on the same chromosome, representing a specific set of genetic variations.

What is a compound heterozygote?

A compound heterozygote is an individual who appears homozygous for a recessive trait but carries two different mutant alleles that originate from different genetic backgrounds.

How does pleiotropy relate to single gene disorders?

Pleiotropy occurs when one gene influences multiple phenotypic traits, meaning that a single gene can have various effects on the body, as seen in conditions like sickle cell disease.

What is penetrance in the context of genetics?

Penetrance refers to the proportion of individuals with a specific genotype who actually express the associated phenotype, indicating that not all individuals with the gene will show the disorder.

What does variable expressivity mean?

Variable expressivity refers to the different degrees to which a phenotype can be expressed among individuals with the same genotype, meaning symptoms can vary in severity.

Why are penetrance and expressivity important in genetic counseling?

These concepts are crucial for genetic counseling as they complicate predictions about disease outcomes in families, making it challenging to determine the likelihood of expression of a genetic condition.

How can inbreeding or consanguinity affect genetic disorders?

Inbreeding or consanguinity can lead to increased chances of inheriting the same mutation from both parents, potentially resulting in a higher prevalence of recessive genetic disorders within families.