Principles of Inheritance and Variation Test - 19

Hemophilia A and hemophilia B are inherited in an X-linked recessive pattern. The genes associated with these conditions are located on the X chromosome, which is one of the two sex chromosomes. In females (who have two X chromosomes), a mutation would have to occur in both copies of the gene to cause the disorder.

When a colour blind man (X^cY) marries a normal woman (XX), all of their daughters are carriers and all of their sons are normal. When the carrier daughter (XX^c) is married to a normal man the probability of their being colour blind is 0.25

It is clear that the probability in the grandson of a colour blind man and normal woman is 0.25.

Klinefelter syndrome is a sex chromosome disorder in boys and men that results from the presence of an extra X chromosome in cells. People typically have 46 chromosomes in each cell, two of which are the sex chromosomes. Females have two X chromosomes (46, XX), and males have one X and one Y chromosome (46, XY).

Men determine the sex of a baby depending on whether their sperm is carrying an X or Y chromosome. An X chromosome combines with the mother's X chromosome to make a baby girl (XX) and a Y chromosome will combine with the mother's to make a boy (XY).

Autosomal recessive disorder refers to a disorder in which an individual is affected only when both the chromosomes carry the affected gene.

Here AA- homozygous dominant;

Aa- heterozygous dominant; aa- homozygous recessive( only in this case the manifestations of the disorder are seen)

A carrier means an individual who carries the affected gene but does not have the disorder so their genotype can be written as Aa (one is dominant, other is recessive so the dominant one is expressed).

When mating takes place:

Aa × Aa (parental generation)

AA, Aa, Aa, aa (possible genotypes of children)--- out of these only children with the genotype 'aa' is affected.

Therefore, 1/4 or 25% of the children are probable to be affected by this disorder.

Sickle cell anemia is an autosomal recessive hereditary disorder in which the erythrocytes become sickle-shaped under oxygen deficiency as during strenuous exercise at high altitudes. The disorder is caused by the formation of abnormal hemoglobin called hemoglobin-S.

Sickle cell disease is an autosomal recessive disease commonly found in African populations. The disease gets its name from the fact that patients’ red blood cells become sickle-shaped when passing through the capillaries of metabolically active tissues. These red blood cells become frail and can rupture long before their normal lifespan. The sickled red blood cells block capillaries and inhibit red blood cell function, causing severe anemia in sufferers.

ABO blood group system, the classification of human blood based on the inherited properties of red blood cells (erythrocytes) as determined by the presence or absence of the antigens A and B, which are carried on the surface of the red cells. Persons may thus have type A, type B, type O, or type AB blood. The A, B, and O blood groups were first identified by Austrian immunologist Karl Landsteiner in 1901.