Pedigree Quiz
Questions: 16 · 10 minutes
1. A woman is a carrier of an X-linked recessive variant, and the father does not carry the variant on his X chromosome. What is the probability that any one son inherits the variant?
0%
25%
50%
100%
2. One parent is heterozygous for a fully penetrant autosomal dominant variant, and the other parent does not carry it. What is each child’s probability of inheriting the variant?
25%
33%
100%
50%
3. An unaffected couple has an affected son and an affected daughter. Assume the trait is rare, fully penetrant, and caused by one gene. Which pattern is most consistent?
Autosomal dominant
Autosomal recessive
Mitochondrial
X-linked dominant
4. A dominant-looking trait seems to skip one generation in a pedigree. Which factor could plausibly explain this without changing the underlying dominant inheritance?
An individual inherited the variant but did not express the trait because of incomplete penetrance
All dominant alleles became recessive in that generation
Males cannot inherit dominant alleles from their mothers
The allele moved from an autosome to a sex chromosome
5. Under a simple autosomal recessive model, two affected parents both have genotype aa. What is expected for their children?
Only sons will be affected
Each child has a 50% chance of being affected
No children will be affected, but all will be carriers
All children will be affected
6. Two offspring branch from the same point in a pedigree. An additional line connects their two diagonal branches. What does that added line conventionally indicate?
They are ordinary siblings born in different pregnancies
They have different biological fathers
They both carry an autosomal recessive variant
They are monozygotic, or identical, twins
7. In a standard human pedigree, which symbol usually represents a male?
A diamond
A circle
A square
A triangle
8. A trait appears only in males, and affected fathers consistently pass it to all their sons. Which inheritance pattern best fits?
X-linked recessive
Y-linked
Mitochondrial
Autosomal recessive
9. Two carriers of the same autosomal recessive variant have a child. What is the probability that the child inherits neither copy of the variant?
0%
25%
75%
50%
10. A pedigree shows clear transmission of a trait from an affected father to his affected son. Which conclusion is most defensible under a standard single-gene model?
The trait is not X-linked
The son's mother must express the trait
The trait must be autosomal dominant
Every daughter of the father must be unaffected
11. What does a horizontal line directly connecting two individuals usually indicate in a pedigree?
They are reproductive partners
They show the same trait
They are identical twins
One is the other's child
12. Why can a pedigree showing biological parents who are close relatives raise suspicion of an autosomal recessive condition?
Related parents always express the same recessive traits
Their sons inherit two X chromosomes more often
Close relationship converts recessive alleles into dominant alleles
They are more likely to share a rare variant inherited from a common ancestor
13. What does an arrow pointing to one person in a pedigree usually identify?
The oldest person in the generation
The proband or person who brought the family to attention
A confirmed carrier in every notation system
The person who introduced the variant into the family
14. A man has an X-linked recessive condition. He has a daughter with a woman assumed not to carry the familial variant. What is the daughter’s expected status under the standard model?
She cannot inherit the variant
She will usually express the condition because her father is affected
She will be an obligate carrier of the paternal variant
She has a 25% chance of carrying the variant
15. An affected father passes a trait to all his daughters and none of his sons. An affected heterozygous mother can pass it to children of either sex. Which pattern best fits?
Autosomal recessive
Y-linked
X-linked dominant
Mitochondrial
16. Which family pattern is characteristic of mitochondrial inheritance in the simplified pedigree model?
Affected mothers can pass the variant to children of any sex, while affected fathers do not transmit it
Affected fathers pass the variant to all daughters only
Either parent passes the variant to exactly half of all children
Affected fathers pass the variant to all sons only