Pedigree X-Linked Traits

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To study the prepared pedigree chart of genetic traits such as colour blindness and haemophilia.

Mendel’s principles of inheritance are applicable to plants, animals, and humans.
Crossbreeding, as done with plants and animals, cannot be applied to humans.
Instead, a pedigree chart records inheritance across multiple generations, illustrating genetic traits in the form of a family tree.
This chart helps analyze the Mendelian concepts of dominance and gene segregation over generations.

A family with a monogenetic trait (e.g., colour blindness or haemophilia) was selected.
Family members were interviewed for relevant genetic information.
The traits were examined in the surviving individuals.
A pedigree chart was created using the gathered information and appropriate symbols.
Careful analysis suggested that the gene responsible for the trait was X-linked and recessive.

Genes are inherited from biological parents in specific ways, one of which is X-linked recessive inheritance.

This form of inheritance occurs when the gene causing the trait or disorder is located on the X chromosome.
Females have two X chromosomes, while males have one X and one Y chromosome.
X-linked recessive genes are expressed in females only if they inherit two copies of the gene.
Males express the trait if they inherit just one copy of the X-linked recessive gene, as they have only one X chromosome.
A carrier female has a 50% chance of passing the trait to her offspring:
50% chance her daughters may carry the gene.
50% chance her sons will express the trait.

Colour blindness or colour vision deficiency reduces the ability to perceive colours or distinguish between them.
It can complicate tasks like choosing ripe fruits, selecting clothing, or reading traffic lights.
Though the condition might pose minor challenges, people adapt well in most cases.
Red-green colour blindness is the most common form, affecting up to 8% of males and 0.5% of females.
Colour blindness results primarily from a genetic problem affecting the color-sensing cones in the eyes.
It is diagnosed using tests such as the Ishihara colour test.
Men are more prone to this condition since they only have one X chromosome, unlike females who typically compensate with their second X chromosome.

Haemophilia is a genetic disorder that impairs the body’s ability to form blood clots, leading to prolonged bleeding after injuries, easy bruising, and an increased risk of internal bleeding.
The two main types are:

Haemophilia is inherited via the X chromosome, and males are more commonly affected.
In rare cases, haemophilia results from spontaneous mutations or the body developing antibodies against clotting factors.
Treatment involves replacing missing clotting factors either during bleeding episodes or on a regular basis.
Advances in gene therapy are under study for treatment.
The condition affects approximately 1 in 5,000 to 10,000 males for Haemophilia A and 1 in 40,000 for Haemophilia B.

Families studied displayed symptoms consistent with X-linked recessive disorders, as revealed by pedigree analysis.

The pedigree analysis confirmed that the genetic traits for X-linked recessive disorders were transmitted across generations in the families studied.

Prior knowledge of genetic disorders is essential for identifying specific conditions in pedigree analysis.
Family history spanning at least 3–4 generations should be available for accurate analysis.