11. The figure below shows a pedigree of a family over three generations with respect
to a genetic disorder. What sort of inheritance is depicted in this pedigree?
a. Autosomal recessive trait
b. Autosomal dominant trait
c. Sex linked trait
d. Codominant trait
The pedigree in the image shows an autosomal dominant trait (Option B) because affected individuals appear in every generation and both sexes are equally affected, with roughly 50% of the offspring of an affected heterozygous parent showing the disorder.
Introduction: autosomal dominant trait pedigree genetic disorder
Pedigree analysis is a core genetics skill used to infer how a genetic disorder is inherited in a family across multiple generations. In this question, the pedigree shows affected individuals in all three generations, with males and females equally likely to be affected, pointing strongly to an autosomal dominant trait. Recognizing these patterns quickly is essential for solving pedigree‑based MCQs in CSIR NET and other competitive exams.
Why option B is correct: autosomal dominant trait
For a trait to be autosomal dominant, three characteristic features appear in a pedigree.
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The trait is present in every generation; dominant traits typically do not skip generations because a single mutant allele is sufficient to express the phenotype.
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An affected individual almost always has at least one affected parent, and when a heterozygous affected parent mates with a normal partner, about 50% of the offspring are affected, matching the pattern described in the slide (~50% affected offspring).
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Males and females are affected in similar proportions, which indicates that the gene lies on an autosome rather than on a sex chromosome.
In the given pedigree, affected individuals are observed in each generation, and both sons and daughters can inherit the disorder from either parent, which fits all the classical rules of autosomal dominant inheritance, so option B is the correct choice.
Why option A is wrong: autosomal recessive trait
Autosomal recessive traits show a very different pedigree pattern from what is seen here.
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Recessive traits often “skip” generations because carriers (heterozygotes) are phenotypically normal; unaffected parents can have affected children when both pass on the recessive allele.
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In many autosomal recessive pedigrees, affected individuals tend to cluster among siblings, and the disorder may suddenly appear in a generation where two carriers mate, rather than being present in every generation.
Since the pedigree in the question shows affected individuals in each generation and resembles a vertical transmission pattern, it does not match the typical features of autosomal recessive inheritance, so option A is rejected.
Why option C is wrong: sex‑linked trait
Sex‑linked traits, especially X‑linked ones, produce a strong sex bias in the pedigree that is not seen here.
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X‑linked recessive disorders usually affect many more males than females, and affected males often inherit the trait from carrier mothers, with no male‑to‑male transmission.
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X‑linked dominant traits often show more affected females than males, and an affected father passes the trait to all daughters but none of his sons; such characteristic patterns are not indicated in this question.
Because the slide explicitly tells that both sexes are equally affected and there is no consistent sex bias or father‑to‑daughter–only transmission, the trait is very unlikely to be sex‑linked, making option C incorrect.
Why option D is wrong: codominant trait
Codominant inheritance refers to a situation where both alleles in a heterozygote are fully and simultaneously expressed, as in the classic ABO blood group system.
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In codominant traits, heterozygotes show a distinct phenotype that simultaneously expresses both alleles rather than simply showing “affected” versus “unaffected,” and pedigrees usually classify three phenotypic categories rather than the binary diseased/normal pattern shown here.
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The question describes a simple presence or absence of a genetic disorder, which follows a dominant–recessive pattern rather than a codominant one, so codominance does not explain the observed inheritance.
Therefore, codominant trait (option D) is not compatible with the pedigree, and the only consistent explanation remains autosomal dominant inheritance (option B).
