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Quizzes > Science

Pedigree analysis quiz: Interpret inheritance patterns

Quick, free pedigree chart quiz to test your knowledge. Instant results.

Editorial: Review CompletedCreated By: Kiroette CallyUpdated Aug 26, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for a pedigree genetics quiz on a golden yellow background

This quiz helps you read pedigree charts and identify autosomal, X-linked, dominant, and recessive traits. Work through clear family trees with instant feedback to build speed and accuracy for class or exams. For more practice, try punnett square practice, a genotype vs phenotype quiz, or a dominant or recessive quiz.

In a standard pedigree chart, which shape represents a male individual?
Triangle
Diamond
Square
Circle
In pedigree charts, males are traditionally depicted as squares while females are circles. This convention helps geneticists quickly identify sex-specific inheritance patterns in a family tree. Recognizing these symbols is fundamental to interpreting pedigree analyses.
What does a filled (shaded) symbol indicate in a pedigree chart?
Unaffected individual
Carrier of trait
Affected individual
Unknown status
In pedigrees, a shaded or filled symbol signifies that the individual exhibits the trait under study. Carriers are often shown as half-shaded in some conventions. Understanding this allows for quick interpretation of affected versus unaffected family members.
In a pedigree chart, a horizontal line connecting a male and a female symbol represents what?
Mating or marriage
Genetic linkage
Adoption
Sibling relationship
A horizontal line between a male and female symbol indicates mating or partnership in pedigree diagrams. Vertical lines descending from that pair show their offspring. This layout helps trace the inheritance of traits across generations.
In a pedigree, a vertical line descending from a couple to a symbol below indicates what?
Mutation event
Carrier status
Offspring
Interrupted inheritance
Vertical lines from parents to a symbol signify the offspring in a pedigree chart. This arrangement visually organizes family members by generation. Recognizing this structure is key to interpreting family inheritance patterns.
What does a double line between two individuals in a pedigree chart usually represent?
Identical twins
Foster relationship
Consanguineous mating
Adoption
A double line indicates consanguinity, meaning the couple shares a common ancestor. Consanguineous matings increase the probability of autosomal recessive disorders. Identifying consanguinity is important for risk assessment in genetic counseling.
If a trait appears in every generation of a pedigree, which mode of inheritance is most likely?
X-linked recessive
Mitochondrial
Autosomal dominant
Autosomal recessive
Autosomal dominant traits typically appear in each generation since only one mutant allele is necessary for expression. Affected individuals have a 50% chance of passing the trait to offspring. In contrast, autosomal recessive traits can skip generations.
When a trait skips generations and appears among siblings, which inheritance pattern does this suggest?
Y-linked
Autosomal dominant
X-linked dominant
Autosomal recessive
Autosomal recessive traits often skip generations because two mutant alleles are required for expression. Carriers are typically unaffected but can pass the allele to offspring. Affected siblings arise when both parents carry and transmit the recessive allele.
In X-linked recessive inheritance, which gender is more frequently affected?
Neither
Both equally
Female
Male
Males have only one X chromosome, so a single mutant allele on that chromosome will cause disease. Females have two X chromosomes, so they are more often carriers. This results in a higher prevalence of X-linked recessive disorders in males.
Which parent transmits mitochondrial DNA to offspring?
Both parents equally
Father
Neither parent
Mother
Mitochondrial DNA is inherited exclusively from the mother because the egg contributes the cytoplasm and mitochondria. Sperm mitochondria are typically destroyed after fertilization. This maternal inheritance pattern is consistent across all offspring.
Which statement best describes Y-linked inheritance?
Trait appears in both sexes but only transmitted by fathers
Trait appears only in males and is passed from father to all sons
Trait skips generations
Trait is transmitted by mothers only
Y-linked traits are located on the Y chromosome and can only be present in males. Affected fathers will transmit the trait to all of their sons. No daughters are affected since they do not inherit a Y chromosome.
In a pedigree chart, what does an open (unshaded) symbol signify?
Carrier status
Unaffected individual
Unknown status
Affected individual
Open or unshaded symbols represent individuals who do not exhibit the trait being studied. This visual distinction helps to track affected versus unaffected family members. Carriers may be indicated differently depending on the pedigree convention.
In pedigree analysis, how is the proband (index case) indicated?
Dotted line
Arrow pointing to the individual
Bold border
Double circle
The proband is the first affected family member who seeks medical attention for a genetic disorder and is marked with an arrow. Identifying the proband is crucial for tracing inheritance patterns in pedigree analysis. This standard notation helps genetic counselors organize family history.
What is the probability that two unrelated carriers of an autosomal recessive allele will have an affected child?
75%
25%
100%
50%
When both parents are carriers of an autosomal recessive allele (Aa x Aa), there is a 1 in 4 chance (25%) that a child will inherit two mutant alleles (aa) and express the trait. The Punnett square for this cross shows one affected genotype among four. Carrier and unaffected probabilities fill the remaining squares.
In an X-linked dominant disorder, what is the expected pattern when an affected father mates with an unaffected mother?
All daughters affected, no sons affected
Half of sons and half of daughters affected
All sons affected, no daughters affected
No children affected
In X-linked dominant inheritance, an affected father (X*Y) passes his mutant X chromosome to all daughters (X*X) making them affected. Sons inherit the Y chromosome from the father and a normal X from the mother, so none are affected. This father-to-daughter transmission is diagnostic.
Which observation in a pedigree strongly suggests autosomal recessive inheritance?
Only males affected
All children of affected mothers are affected
Trait appears among siblings of unaffected parents
Trait in every generation
Autosomal recessive traits often emerge in offspring of two carrier parents who themselves are unaffected. This results in the phenotype skipping generations and appearing among siblings rather than direct parent-child transmission. Observation of affected siblings from unaffected couples is characteristic.
Which pedigree pattern indicates an X-linked recessive disorder?
All daughters of affected fathers are unaffected
Many more males affected with no father-to-son transmission
Equal numbers of affected males and females
Trait present in every generation
X-linked recessive traits disproportionately affect males since they have only one X chromosome. Affected fathers cannot pass the mutant allele to sons (no father-to-son transmission) but all carrier daughters. A skewed male-to-female ratio and this transmission pattern are diagnostic.
A carrier mother of an X-linked recessive disorder and an unaffected father have a son. What is the probability the son is affected?
75%
25%
50%
0%
Carrier females (X*X) have a 50% chance of transmitting the mutant X chromosome to a son (X*Y), leading to the disease. Sons inheriting the normal X (XY) are unaffected. Punnett square analysis clarifies this risk for each male offspring.
What is the probability that a child of a carrier mother and unaffected father is a carrier daughter for an X-linked recessive trait?
0%
50%
25%
100%
Carrier mothers (X*X) have a 50% chance of passing the mutant X to daughters. Daughters who inherit the mutant X and a normal X from the father become carriers. Sons either are affected or unaffected but cannot be carriers.
Consanguinity in a pedigree increases the risk of which type of inheritance?
Autosomal dominant
Autosomal recessive
X-linked dominant
Mitochondrial
Consanguineous matings raise the probability that both parents carry the same recessive allele inherited from a common ancestor. This increases the chance of autosomal recessive disorders manifesting in offspring. Genetic counselors pay special attention to consanguinity when assessing risk.
If the proband's genotype is aa for an autosomal recessive trait, what is the probability that an unaffected sibling is a carrier?
1/3
1/4
2/3
1/2
When two carrier parents (Aa x Aa) have an affected child (aa), the remaining two unaffected children have either AA or Aa. Excluding the aa outcome leaves three possibilities: AA, Aa, Aa. Two of these are carriers, so the probability an unaffected sibling is a carrier is 2/3.
Which feature in a pedigree is most indicative of mitochondrial inheritance?
Affected mothers transmit to all offspring, while affected fathers do not transmit
Trait appears only in males
Affected fathers transmit to all sons only
Trait skips multiple generations
Mitochondrial DNA is inherited exclusively from the mother, so all children of an affected mother inherit the trait. Fathers cannot pass mitochondrial mutations to offspring. This distinctive transmission pattern signals mitochondrial inheritance.
Why are there no male 'carriers' in X-linked dominant inheritance?
Dominant alleles skip male expression
Affected males express the trait fully since only one X chromosome is present
Males have an extra X chromosome
Trait is lethal in males
In X-linked dominant disorders, a single copy of the mutant allele in males (who have one X) leads to full expression of the trait. There is no normal allele to mask the effect, so males are always affected rather than being carriers. Heterozygous females may show variable expressivity.
Which observation suggests genomic imprinting?
Phenotype depends on whether the allele is inherited from the mother or father
Equal expression in both sexes
Phenotype only in homozygotes
Trait exhibits 100% penetrance
Genomic imprinting results in parent-of-origin specific gene expression, so the same allele can produce different phenotypes depending on maternal or paternal inheritance. This epigenetic phenomenon is distinct from classical Mendelian inheritance. Disorders like Prader-Willi and Angelman illustrate imprinting effects.
What term describes when individuals carry a disease-causing genotype but do not exhibit the phenotype?
Anticipation
Incomplete penetrance
Locus heterogeneity
Variable expressivity
Incomplete penetrance occurs when not all individuals with a mutant genotype display the associated phenotype. This can complicate pedigree analysis since some carriers appear unaffected. Penetrance is quantified as the proportion of individuals with the genotype who exhibit the phenotype.
Which term describes varying severity of phenotype among individuals with the same genotype?
Allelic heterogeneity
Genetic anticipation
Incomplete penetrance
Variable expressivity
Variable expressivity refers to differences in the severity or range of symptoms observed among individuals with the same disease-causing genotype. This variability can be due to modifier genes, environment, or stochastic factors. Recognizing variable expressivity is crucial in clinical genetics.
Which genetic phenomenon is characterized by earlier onset or increased severity in successive generations?
Epistasis
Locus heterogeneity
Anticipation
Genetic imprinting
Anticipation is observed in disorders like Huntington disease and myotonic dystrophy, where trinucleotide repeat expansions increase in size across generations. This leads to earlier onset or more severe manifestations in offspring. Tracking anticipation requires detailed pedigree and molecular analysis.
A cross between two heterozygotes for a recessive lethal allele often yields which phenotypic ratio among surviving offspring?
2 affected : 1 unaffected
3 affected : 1 unaffected
1 affected : 1 unaffected
All unaffected
When homozygous recessive (aa) is lethal, those embryos do not survive. A cross Aa x Aa theoretically produces offspring genotypes in a 1 AA : 2 Aa : 1 aa ratio, but the aa genotype is lethal. Excluding aa yields a 2:1 ratio of heterozygotes to homozygous normals among survivors.
What does allelic heterogeneity refer to?
Mutations in different genes cause the same phenotype
Different mutations in the same gene cause similar phenotypes
One gene influences multiple traits
Genes are located on different chromosomes
Allelic heterogeneity occurs when different mutations (alleles) at the same genetic locus produce the same or similar disease phenotype. Cystic fibrosis is an example where many CFTR gene mutations can cause the disorder. This concept is distinct from locus heterogeneity.
What is locus heterogeneity?
Multiple genes interact to produce one trait
Mutations in different genes lead to the same phenotype
Different mutations in the same gene produce varied phenotypes
Gene expression varies by tissue
Locus heterogeneity describes the situation where mutations in different genes can cause the same clinical condition. For example, genetically distinct forms of retinitis pigmentosa arise from mutations in multiple different genes. This can complicate molecular diagnosis strategies.
What term describes the survival advantage of heterozygous genotype in certain populations?
Heterozygote advantage
Founder effect
Penetrance
Expressivity
Heterozygote advantage refers to the phenomenon where carriers of a single mutant allele have a selective advantage, such as protection against malaria in sickle cell trait (HbAS). This maintains the allele at higher frequencies in certain populations. It exemplifies balancing selection in evolution.
What is the coefficient of inbreeding (F) for children of first cousins?
1/4
1/8
1/16
1/32
The coefficient of inbreeding (F) measures the probability that an individual's two alleles at a locus are identical by descent. For first-cousin offspring, F = 1/16 because their parents share 1/8 of their genes, and the offspring have half that probability for alleles from a common ancestor. This guides risk assessment in consanguineous families.
Which term describes variable phenotype due to differing mutant mitochondrial proportions?
Allelic heterogeneity
Mitochondrial heteroplasmy
Genetic anticipation
Locus heterogeneity
Mitochondrial heteroplasmy refers to the presence of a mixture of normal and mutant mitochondrial DNA within cells. The proportion of mutant mitochondria can vary between tissues and individuals, leading to variable expressivity of mitochondrial diseases. Understanding heteroplasmy is key for predicting disease severity.
Prader-Willi syndrome is most commonly caused by which genetic event?
Mutation in the CFTR gene
Trinucleotide repeat expansion
Deletion of the maternal 15q11-q13 region
Deletion of the paternal 15q11-q13 region
Prader-Willi syndrome often results from a deletion of the paternal allele on chromosome 15q11-q13, coupled with maternal imprinting of that region. This parent-of-origin effect leads to absence of paternal gene expression. Alternative mechanisms include maternal uniparental disomy.
Angelman syndrome typically arises from which genetic alteration?
Deletion of the paternal 15q11-q13 region
Point mutation in the INS gene
Deletion of the maternal 15q11-q13 region
Duplication of 15q11-q13
Angelman syndrome is often caused by deletion or inactivation of the maternal copy of the 15q11-q13 region, with the paternal allele being imprinted (silenced). This leads to loss of maternal UBE3A expression in the brain. Other causes include paternal uniparental disomy of chromosome 15.
Which formula is used to calculate the LOD (logarithm of odds) score in linkage analysis?
P(data | ?) - P(data | ? = 0.5)
log2[P(data | ?) / P(data | ? = 0.5)]
log10[P(data | ? = 0.5) / P(data | ?)]
log10[P(data | ?) / P(data | ? = 0.5)]
The LOD score compares the likelihood of observed data under a given recombination fraction (?) versus no linkage (? = 0.5). It is calculated as the base-10 logarithm of the ratio of these probabilities. A positive LOD indicates evidence for linkage.
In linkage analysis, a LOD score of -2 or less indicates what?
Significant evidence against linkage
Strong evidence for linkage
Equivocal evidence for linkage
No information on linkage
A LOD score ? -2 is considered significant evidence against linkage between two loci, suggesting they assort independently. Conventionally, a LOD ? 3 indicates significant evidence for linkage. Values between -2 and 3 are inconclusive.
Which recombination fraction (?) corresponds to a genetic distance of 25 centimorgans (cM)?
0.25
1.0
0.1
0.5
By definition, 1 cM approximates a 1% recombination frequency. Therefore, 25 cM corresponds to a recombination fraction (?) of 0.25. ? = 0.5 represents independent assortment (50%). This calculation is fundamental in constructing linkage maps.
What LOD score is generally accepted as significant evidence of linkage in human genetic studies?
-2 or less
3 or greater
1 or greater
0
A LOD score of 3 corresponds to an odds ratio of 1000:1 in favor of linkage, which is the conventional threshold for declaring significant linkage in human genetics. Scores between -2 and 3 are inconclusive, while ? -2 argue against linkage. This threshold balances type I and type II errors.
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Study Outcomes

  1. Interpret Pedigree Symbols -

    Identify and understand standard symbols and notations used in pedigree charts to map family relationships and trait occurrences.

  2. Differentiate Inheritance Modes -

    Distinguish between autosomal dominant, autosomal recessive, and X-linked inheritance patterns in various family trees.

  3. Analyze X-Linked Traits -

    Examine pedigree examples to determine how X-linked traits are transmitted through maternal and paternal lines.

  4. Predict Trait Transmission -

    Apply probability concepts to forecast the likelihood of specific genetic traits appearing in future generations.

  5. Apply Pedigree Analysis Techniques -

    Use systematic approaches to solve pedigree genetics quiz scenarios and accurately infer genotypes of family members.

  6. Evaluate Real-World Pedigrees -

    Assess sample pedigrees from real or simulated cases to reinforce your understanding of genetics inheritance quiz principles.

Cheat Sheet

  1. Autosomal Inheritance Patterns -

    Autosomal dominant traits appear in every generation, while autosomal recessive traits can skip generations; practice with Punnett squares (e.g., Aa × Aa yields a 1:2:1 genotypic ratio). Remember "Dominant Does Display," a quick mnemonic that dominant traits will always show if at least one allele is present. Reviewing examples like cystic fibrosis (recessive) vs. Huntington's disease (dominant) from university genetics courses helps solidify these patterns.

  2. X-Linked Traits Interpretation -

    X-linked recessive traits often affect males more severely since they have only one X chromosome (e.g., colorblindness). Use the phrase "X Marks the Spot" to recall that the defective allele is on the X chromosome - females need two copies to express, while males need only one. Checking pedigree squares (males) and circles (females) for shaded symbols will help you ace the X-linked traits quiz section.

  3. Pedigree Symbols & Conventions -

    Standard symbols include squares for males, circles for females, shaded shapes for affected individuals, and arrows indicating the proband; knowing these conventions lets you quickly interpret any pedigree genetics quiz. Annotate each generation with Roman numerals (I, II, III) and individuals with Arabic numerals (1, 2, 3) to track inheritance clearly. Reliable guides from genetics textbooks and NIH resources reinforce these symbolic rules.

  4. Calculating Carrier Risks -

    When parents are unaffected but have an affected child, use conditional probability (e.g., a 2/3 chance a sibling is a carrier in autosomal recessive pedigrees) to predict risk. Constructing small Punnett squares and applying Bayes' theorem helps refine carrier probability estimates in complex families. Practice problems from reputable university problem sets will sharpen your pedigree analysis quiz skills.

  5. Recognizing Non-Mendelian Patterns -

    Mitochondrial inheritance passes exclusively from mother to all children, so look for maternal-line only transmission - no male-to-offspring transmission ever. Remember "Maternal Mitos Always Matter" as a mnemonic to distinguish these traits from autosomal or X-linked patterns. Reviewing case studies in genetics journals ensures you spot exceptions on your genetics inheritance quiz.

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