Question

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

A. Sickle cell anemia
B. Hemophilia
C. Thalassemia
D. Phenylketonuria

Answer 1

Hint: There are 23 pairs of chromosomes in every single human cell, for a total of 46 chromosomes. A phenotype is any feature determined by a gene and is often determined by more than one gene. Mutated genes that are inherited or that are the result of a new gene mutation are caused by certain characteristics.

Complete answer:
The pattern suggests that the feature is inherited from mother to son and from dad to daughter. As we know, there are XY sex chromosomes for human males and XX sex chromosomes for human females. The mother's X chromosome is always inherited by a son and the father's Y chromosome, while the father always transfers his X chromosome to his daughters. An X-linked trait is often transmitted from mother to son and from father to daughter; hence, the trend demonstrates X-linked trait inheritance. If it were an autosomal trait, regardless of the child's sex, both parents would have passed it on with equal likelihood to all the offspring.
Phenylketonuria- It is an inborn metabolic error and is caused by a mutation found on chromosome 12 in the PAH gene. In an autosomal recessive form, it is inherited and therefore does not follow the pattern shown.
Sickle cell anaemia- is caused by a point mutation in the haemoglobin beta-globin (Hbb) chain gene found on chromosome 11. It is also inherited in a recessive autosomal manner and therefore does not follow the pattern shown.
Thalassemia- is a group of blood disorders caused by mutations found on chromosome 11 and chromosome 16 in the HbB and HbA genes, respectively. They are thus inherited in a recessive autosomal way.
Haemophilia is a sex-linked condition since there is an X-chromosome that is a human sex chromosome found in the controlling genes. The phenotype is transmitted in a sex-linked manner to offspring.

Hence, the correct answer is option (B).

Note: Hemophilia is a genetic disorder that is hereditary. This disorder is not curable, however to alleviate symptoms and avoid potential health problems, it can be treated. In extremely rare cases, after birth, haemophilia may develop. This is called haemophilia acquired.