Question

What is sex-linked inheritance? Give two examples.

Answer 1

Sex-linked inheritance:

1. The transmission to the future generation of various traits that are because of alleles at gene loci on a sex chromosome is known as sex-linked inheritance.
2. In vertebrates, the female is homogametic, with two X chromosomes (XX), while the male is the heterogametic sex, with one X and one Y chromosome (XY).
3. The genes that are present on the X or Y chromosome are called sex-connected.
4. In this way, sex-linked diseases are transmitted by sex chromosomes only.

Examples are as follows:

1. Red-green color blindness:

1. The people who suffer from this red-green color blindness cannot distinguish between these two colors
2. The gene which causes this defect is present on the X-chromosome and that is why this is generally seen in males.
3. It was first observed by a scientist named Horner in the year 1876.

2. Hemophilia:

1. It is caused by a mutant gene (h) present in the X chromosome and it is recessive to the normal gene and is, therefore, suppressed in the heterozygous condition. Individuals suffering from this disease lack the factor which is responsible for the clotting of blood.
2. So as the clotting factor of blood is missing a small cut can lead to severe blood loss which can even lead to death.
3. This disease generally occurs in males.

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