Study the pedigree chart given below. What does it show?

A. This pedigree chart is wrong as this is not possible.
B. Inheritance of a recessive sex-linked disease like haemophilia.
C. Inheritance of a sex-linked inborn error of metabolism like phenylketonuria.
D. Inheritance of a condition like phenylketonuria as an autosomal recessive trait.

Hint: Pedigree chart refers to a diagram which represents the appearance and occurrence of phenotypes of an organism or a particular gene inherited from its ancestors from one generation to the next generation. A pedigree chart is an easily readable chart which gives information about a family.

Complete answer: In simple words pedigree charts can be called family trees. Standardized sets of symbols are used in pedigree charts. Squares in pedigree charts represent males and circles in pedigree charts denote female members of a family. Horizontal lines connect the parents and Offsprings are connected by vertical lines. The pedigree chart shows the family history and details about an earlier generation. A diamond symbol is used if the sex of the person is unknown. The phenotype of the individual is shown with the help of filling the square or circles of the pedigree chart. Option A is wrong as the given pedigree chart is not wrong. The above-given pedigree chart shows an autosomal recessive disorder. In this pedigree chart, the trait is not expressed by both parents. If the parents are carriers of abnormal genes, then their offspring can express the trait. Therefore, the above pedigree chart shows the inheritance of a condition like phenylketonuria as an autosomal recessive trait.
So, option D is the correct answer.

Note: A generation is skipped in autosomal recessive disorder. Therefore, offspring with the trait have normal parents who act as a carrier and are not affected by abnormal genes. Both male and females are likely to be affected by the autosomal recessive disorder.