Question

Represented below is the inheritance pattern of a certain type of trait in humans. Which of the following could be an example for this type of inheritance?

• A. Colour blindness
• B. Sickle cell anaemia
• C. Phenylketonuria
• D. Thalassemia

Answer 1

The correct option is A Colour blindness

In the diagram given in the question, a line can be seen emanating from the mother and reaching the son. Another similar line can be seen emanating from the father to the daughter. This points toward a specific type of inheritance called criss-cross inheritance. In such an inheritance pattern, a specific gene is passed on from parents to offspring of the opposite gender. Here, the mother passes on the gene to her son, while the father passes on the gene to his daughter. This is possible in case of X-linked inheritance of traits. It is because the inheritance pattern of sex chromosomes is different from that of autosomes, especially in the case of males. Fathers pass on their X chromosomes to their daughters and Y chromosomes to their sons, whereas the passing down of autosomes follows no such rules. Among all the given options, colour blindness is an X-linked recessive trait. Hence the diagrammatic representation can depict the transmission of colour blindness.

Sickle cell anaemia is an autosomal recessive trait which results in the change of the structure of RBCs (red blood cells) from biconcave to sickle-shaped.

Phenylketonuria is an autosomal recessive trait that occurs due to the inability of the body to metabolise an amino acid named phenylalanine.

Thalassemia is an autosomal recessive disorder in which the patient is unable to produce an adequate amount of haemoglobin in the body.