Question

An X-linked recessive trait is?
A. Colour blindness
B. Hunter’s syndrome
C. Sickle-cell anaemia
D. Leishman’s syndrome

Answer 1

X-linked recessive inheritance is a mode of inheritance in which the phenotype is mostly expressed in males through a mutation in a gene on the X chromosome and zygosity in females who are homozygous for gene mutation (which are necessarily homozygous for gene mutation because they have one X and one Y chromosome). Carriers are females with one copy of the mutated gene.

Complete answer: Color blindness or deficiency of colour vision is the reduced ability to see colour or colour differences. Tasks such as picking ripe fruit, choosing clothes and reading traffic lights can be impaired. Colour blindness can make it more challenging for certain educational activities. However, difficulties are generally mild, and most colour-blind people adapt. X-linked are traits that are calculated by alleles borne on the X chromosome. A particular notation is required for X-linked alleles: Xc or X+ where the '+' represents the dominant allele and the recessive allele is the lowercase letter. There are two X-linked alleles for females (because females are XX), while males have only one X-linked allele (because males are XY). In humans, most X-linked genes are recessive. Red-green colourblindness is one instance of an X-linked trait. The recessive allele causing colour blindness is represented by (Xc) and the normal dominant allele is represented by (X+). There is a natural colour vision for women who are X+X+ or X+Xc, while XcXc females are colourblind. Although XcY males are colourblind, males that are X+Y have natural colour vision.
Hence, option A is the correct answer.

Note: There is no cure for colour blindness. Diagnosis can allow the teacher of a person to change the teaching method to accommodate the disability. Special lenses in bright light may help individuals with red-green colorblindness. Mobile apps may help individuals identify colours.