The physical characteristics, which are also known as physical/phenotypic traits in the field of genetics, that are determined by the genes present on the sex chromosomes (allosomes), i.e., the X and Y chromosomes are known as sex-linked characteristics or sex-linked traits. The primary criteria for any of the traits to be sex-linked characters are that they should be a physical aspect of the functional product of a gene that is present on either of the two sex chromosomes. Hence, sex-linked characters are those characters that can be linked to the inheritance and presentation of a gene that is present on a sex chromosome rather than an autosome.
- Haemophilia is a genetic disorder. It is an X- linked chromosome disease in which X carries a non-functional gene. It is of two types haemophilia A which occurs due to low amount of clotting factor VIII, haemophilia B which occurs due to low level of clotting factor IX.
- The haemophilia is an X-linked recessive gene. It means females are the carrier of haemophilia. It will be only expressed if the female combination is double recessive.
- If a haemophilic carrier mother which means haemophilia is expressed in the recessive gene expressed as Xx where x represents the recessive haemophilia X linked gene is crossed with the normal man whose gene is represented as XY. The offsprings would be as follows-
The offspring produced are 50% females in which out of 2 one daughter is the carrier and one is normal. And in case of sons, one is normal and the other is diseased.
