**Question:** Which one of the following is NOT a feature of autosomal recessive disorder?

A. Autosomal recessive disorders affect both males and females equally.
B. These disorders are caused by mutations in mitochondrial DNA.
C. Symptoms usually appear in early childhood.
D. These disorders are often associated with consanguineous marriages.

**Core Concept:** Autosomal recessive disorders are genetic conditions that occur when an individual inherits two copies of a mutated gene from their parents (one from each parent), typically due to consanguineous marriages. These disorders affect both males and females equally. Mutations in mitochondrial DNA are not responsible for autosomal recessive disorders, which are mainly caused by mutations in the individual's nuclear DNA.

**Why the Correct Answer is Right:** Autosomal recessive disorders involve the inheritance of two mutated alleles (variants of a gene) from both parents. In contrast, mutations in mitochondrial DNA are inherited in a maternally dominant manner, meaning only the mother passes on mitochondrial DNA to her offspring. Therefore, option B is incorrect as it discusses mutations in mitochondrial DNA, not autosomal recessive disorders.

**Why Each Wrong Option is Incorrect:**

**Option A**: Autosomal recessive disorders affect individuals regardless of their sex, as they are caused by mutations in the individual's nuclear DNA. This option is incorrect because it generalizes the condition based on sex rather than the genetic cause.

**Option C**: Early childhood onset is not a defining feature of all autosomal recessive disorders. While some disorders may manifest in early childhood, others may present in adulthood or even later in life. This option is incorrect because it assumes that all autosomal recessive disorders have an early childhood onset.

**Option D**: Autosomal recessive disorders are more common in areas with high rates of consanguineous marriages (marriages between relatives). Although consanguineous marriages can increase the risk of autosomal recessive disorders, these disorders can also occur in individuals from non-consanguineous unions due to random assortment of chromosomes during gamete formation. This option is incorrect because it implies that autosomal recessive disorders are exclusively associated with consanguineous marriages, which is not always the case.

**Clinical Pearl:** Autosomal recessive disorders are genetic conditions caused by inheriting two mutated alleles for a gene from one's parents. While consanguineous marriages can increase the risk of these disorders, other factors such as environmental exposures or random assortment of chromosomes during gamete formation can also lead to autosomal recessive disorders.