8. The following the inheritance pattern of a trait under observation:
(i) The trait often skips a generation
(ii) The number of affected males and females is almost equal
(iii) The trait is often found in pedigrees with consanguineous marriages.
The trait is likely to be
(1) autosomal recessive.
(2) autosomal dominant.
(3) sex-linked recessive.
(4) sex linked dominant.

The correct inheritance pattern is autosomal recessive. This is inferred from the trait skipping generations, affecting males and females equally, and appearing frequently in consanguineous marriages.​

Question restatement

The trait under observation shows:

• It often skips a generation.

• The number of affected males and females is almost equal.

• It is often seen in pedigrees with consanguineous marriages.​

Options:

1. Autosomal recessive

2. Autosomal dominant

3. Sex‑linked recessive

4. Sex‑linked dominant

Why autosomal recessive is correct (Option 1)

Autosomal recessive traits commonly skip generations because affected individuals are usually born to unaffected carrier parents; such traits appear only when an individual is homozygous recessive. Equal numbers of affected males and females indicate that the responsible gene is on an autosome rather than a sex chromosome.​

Consanguineous marriages increase the chance that both partners carry the same rare recessive allele, so autosomal recessive traits appear more frequently in such pedigrees. Putting these three clues together—generation skipping, equal sex ratio, and association with consanguinity—clearly indicates autosomal recessive inheritance.​

Why autosomal dominant is incorrect (Option 2)

Autosomal dominant traits usually appear in every generation; an affected child typically has at least one affected parent, so true generation skipping is uncommon. Although autosomal dominant traits also affect males and females equally, they are not characteristically enriched in consanguineous marriages because a single dominant allele is enough for expression, regardless of relatedness of parents. Therefore, the “skips a generation” pattern directly contradicts autosomal dominant inheritance.​

Why sex‑linked recessive is incorrect (Option 3)

X‑linked recessive traits usually affect males much more frequently than females, because males express the phenotype with only one mutant X chromosome while females must be homozygous. The question clearly states that affected males and females are “almost equal,” which is not typical for X‑linked recessive traits. Consanguinity mainly amplifies autosomal recessive conditions; it does not specifically create an equal male:female pattern for X‑linked recessive traits, so this option does not fit all clues.​

Why sex‑linked dominant is incorrect (Option 4)

X‑linked dominant traits often show more affected females than males, because females have two X chromosomes and each has a chance to carry the dominant allele. Furthermore, X‑linked dominant inheritance follows characteristic patterns such as no father‑to‑son transmission and frequent father‑to‑daughter transmission, which are not described in the question, and these traits also do not typically skip generations. Hence, the described observations do not match a sex‑linked dominant pattern.​

SEO‑oriented introduction

In human pedigree analysis, recognizing autosomal recessive inheritance becomes straightforward when a trait repeatedly skips generations, affects males and females in roughly equal numbers, and appears more often in families with consanguineous marriages. These three hallmark features allow students and exam aspirants, including those preparing for CSIR NET Life Sciences, to distinguish autosomal recessive traits from autosomal dominant and sex‑linked patterns with high confidence.​