Genetics Chapter Quiz: Traits and Allele Sharing

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Questions and Answers

Which of the following traits is considered a quantitative trait?

Hypertension

Obesity

Height (correct)

Short stature

How many alleles on average do siblings share at a given locus?

0.75 alleles

0.5 alleles

1 allele (correct)

2 alleles

What does familial aggregation refer to in relation to disease?

The total number of alleles shared among large family groups

The genetic risk of disease unrelated to family history

The likelihood of an affected individual having more affected relatives than expected (correct)

The frequency of disease in unrelated individuals

Which of the following best describes the relationship between monozygotic twins in terms of shared alleles?

They share all their alleles at every locus. Signup and view all the answers

What is the expected average number of alleles shared between a parent and child at every locus?

50% of alleles Signup and view all the answers

What effect does increasing familial relatedness have on the probability of disease?

It increases the probability due to shared alleles. Signup and view all the answers

What is a primary way to measure familial aggregation of a disease?

Comparing disease frequency in affected relatives with prevalence in the general population Signup and view all the answers

Which of the following statements about allele sharing is true?

Parent-child pairs share exactly one allele per locus. Signup and view all the answers

What characteristics distinguish multifactorial disorders from single-gene disorders?

They are caused by complex interactions among multiple genetic variants. Signup and view all the answers

What does the term 'qualitative trait' imply in the context of multifactorial disorders?

It describes diseases that are either present or absent. Signup and view all the answers

Which of the following correctly describes how multifactorial disorders cluster among family members?

They tend to cluster because family members share more genetic and environmental factors. Signup and view all the answers

Which example is regarded as a quantitative trait in multifactorial disorders?

Blood pressure measurement. Signup and view all the answers

Which of the following diseases is an example of a multifactorial disorder?

Alzheimer disease. Signup and view all the answers

What does 'complex inheritance' refer to in the context of multifactorial disorders?

Inheritance that results from interactions between multiple genes and environmental influences. Signup and view all the answers

Which of these is a primary cause of disease susceptibility in multifactorial disorders?

Environmental exposure combined with genetic variations. Signup and view all the answers

Why is the identification of qualitative traits sometimes challenging?

They often involve symptomatic representations. Signup and view all the answers

What does a positive correlation between cholesterol measurements in patients and their relatives indicate?

Higher cholesterol levels in patients are associated with higher levels in their relatives. Signup and view all the answers

How is heritability (H²) defined in the context of quantitative traits?

The fraction of phenotypic variance due to allelic variation. Signup and view all the answers

What does a higher heritability value (H²) suggest about a trait?

Genetic differences play a substantial role in the trait's variability. Signup and view all the answers

Which of the following is a characteristic of multifactorial congenital malformations?

They can be caused by both genetic factors and environmental exposures. Signup and view all the answers

What is the prevalence of congenital heart defects (CHDs) at birth?

Approximately 4 to 8 per 1000 births. Signup and view all the answers

Which mental illness is noted as one of the most severe among the described disorders?

Bipolar disease Signup and view all the answers

What percentage of the human population is affected by schizophrenia worldwide?

Approximately 1% Signup and view all the answers

Which of the following factors is NOT mentioned as a genetic contributor to congenital malformations?

Nutritional deficiencies Signup and view all the answers

What is the most significant risk factor for developing Alzheimer disease?

Age, sex, and family history Signup and view all the answers

What percentage of the United States population is affected by Alzheimer disease?

1% to 2% Signup and view all the answers

Which of the following best characterizes Alzheimer disease?

A chronic, progressive loss of memory and cognitive functions Signup and view all the answers

What is the greatest challenge currently faced in the field of medical genetics regarding complex diseases?

Understanding interactions between genetic variants and environmental factors Signup and view all the answers

How does the risk for Alzheimer disease change with age?

It increases substantially once a person reaches 65 years of age Signup and view all the answers

What does a relative risk ratio (λr) value of 1 indicate?

There is no difference in disease likelihood between relatives and the general population. Signup and view all the answers

How does population prevalence affect the relative risk ratio (λr)?

Higher population prevalence may lead to misinterpretation of familial aggregation. Signup and view all the answers

Which aspect is NOT typically considered in a case-control study assessing familial aggregation?

Genetic mutations specific to cases Signup and view all the answers

What does a larger value of λr indicate regarding familial aggregation?

Increased likelihood that relatives share alleles predisposing to the disease. Signup and view all the answers

What does the coefficient of correlation (r) measure in the context of familial correlation?

The similarity of a physiological measurement among relatives. Signup and view all the answers

In a case-control study, what is compared regarding family history?

The frequency of positive family history among cases compared to controls. Signup and view all the answers

A higher relative risk ratio is often interpreted in the context of:

A genetic predisposition leading to elevated disease occurrence among relatives. Signup and view all the answers

Which of the following statements is true regarding familial aggregation?

The likelihood of disease among relatives can be influenced by genetic factors. Signup and view all the answers

What is the primary characteristic of digenic inheritance as illustrated by retinitis pigmentosa?

It involves the effect of alleles at two different loci. Signup and view all the answers

How does the environmental influence interact with genetic factors in hypercoagulability states?

It enhances the risk of thrombophilia when combined with genetic factors. Signup and view all the answers

In Hirschsprung disease, what is primarily lacking in the affected areas of the colon?

Intrinsic ganglion cells Signup and view all the answers

Which type of diabetes is commonly associated with familial aggregation?

Type 1 diabetes Signup and view all the answers

What defines the phenotypic expression of retinitis pigmentosa in affected families?

Affected individuals are double heterozygotes for mutations at two loci. Signup and view all the answers

What is the consequence of having an aganglionic colon in Hirschsprung disease?

Severe constipation and megacolon Signup and view all the answers

In the context of digenic inheritance for retinitis pigmentosa, what is the key genetic characteristic of affected individuals?

They are heterozygous for two different mutant alleles. Signup and view all the answers

Which of the following is a defining characteristic of type 2 diabetes in familial cases?

It typically represents a higher percentage of cases than type 1 diabetes. Signup and view all the answers

Study Notes

Common Multifactorial Disorders

Common diseases like birth defects, heart attacks, cancers, neurological disorders, diabetes, and Alzheimer's disease significantly impact human health, affecting about two-thirds of individuals.
These diseases often run in families. Relatives of affected individuals show a higher incidence than the general population but don't follow Mendelian inheritance patterns.
Multifactorial disorders result from complex interactions of multiple genetic variants and environmental exposures, possibly including random events.

Qualitative and Quantitative Traits

Qualitative traits are either present or absent (e.g., lung cancer). Diagnosis is usually straightforward, but fine details may require special tests.
Quantitative traits are measurable physical or biochemical quantities in a range (e.g., height, blood pressure). Diagnoses like short stature, high blood pressure, or obesity involve values falling outside the typical range within a population.

Familial Aggregation

Close relatives share more genetic material and environmental exposures than unrelated individuals from a population, increasing their likelihood of similar disease outcomes if there's a genetic predisposition.
Relative Risk Ratio (λ): Compares the prevalence of a disease in relatives of an affected person to the prevalence in the general population; a value greater than 1 indicates a higher risk for the relative compared to the general population risk.
Family History Case-Control Studies: Compare cases (individuals with a disease) to controls (similar individuals without the disease) to assess the family history of each. They are used for possible genetic contributions by examining frequency of positive family histories amongst the cases and the controls.

Heritability and Twin Studies

Heritability (H²): A measure of the genetic contribution to phenotypic variation in a population (0 to 1).
Twin studies: MZ twins share the exact same genetic material, while DZ twins share 50%. Comparing disease concordance rates in MZ vs. DZ twins provides evidence for genetic involvement in a condition.
Disease concordance rates less than 100% in MZ twins imply environmental or other factors play a role. Similar concordance between reared together vs apart also implies a genetic component.

Examples of Multifactorial Diseases

Congenital Heart Defects (CHDs): A group of conditions with both genetic and nongenetic influences/environmental factors, such as teratogenic exposures.
Schizophrenia and Bipolar Disorders: Mental disorders with notable familial aggregation and a complex genetic and environmental contribution.
Type 1 Diabetes Mellitus (T1D): An autoimmune disease where the genetic component involves the major histocompatibility complex (MHC), in particular genes that regulate immune response. It is more prevalent in certain ethnic groups and appears to have a complex interplay of genetics and environment contributing to disease development.
Coronary Artery Disease (CAD): A common cause of morbidity and mortality that demonstrates both genetic (e.g., factor V Leiden, prothrombin) and environmental (diet, exercise, smoking) risk factors. Family and twin studies clearly indicate that genetics does play a role.
Hirschsprung Disease: A developmental issue in the enteric nervous system in the gut. Several regions across the genome, including RET, may be involved in this genetic disease.
Alzheimer's Disease: A progressive neurodegenerative disorder that is more common in older populations. It includes genetic risk factors, notably apolipoprotein E (APOE), but environmental factors or other genetic contributions also play a role.

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Description

This quiz covers key concepts in genetics, focusing on quantitative traits, familial aggregation, and allele sharing between siblings and twins. Test your understanding of how genetic relatedness influences disease probability and allele inheritance. Ideal for students studying genetics and heredity.