SRY - Sex Determining region Y
TDF - Testes Determining Factor

Gypsy moth, fishes, reptiles and birds

Wiener proposed the existence of eight alleles (R¹, R², R⁰,R^Z, r, r¹, r¹¹, r^Y) at a single Rh locus. All genotypes carrying a dominant 'R allele' (R^l, R² ,R⁰,R^Z)will produce 'Rh-positive' phenotype and double recessive genotypes (rr, rr¹, rr¹¹, rr^y) will give rise to Rh-negative phenotype.

The possible genotypes of a B-blood group person are I^BI^Bor I^Bl^O.

The I gene exists in three forms: l^A, I^B and 1^O. The alleles are located on chromosome 9.

When two different incompatible blood types are mixed, agglutination (clumping together) of erythrocytes (RBC) occurs. The basis of these chemical differences is due to the presence of antigens (surface antigens) on the membrane of RBC and epithelial cells.

Antigens A and Antigen B was discovered by Karl Landsteiner. Antigen AB was discovered by Von De Castelle and Sturli.

When three or more alleles of a gene that control a particular trait occupy the same locus on the homologous chromosome of an organism, they are called multiple alleles and their inheritance is called multiple allelism.

(i) Rh factor is a immunogenic D antigen of the Rh blood group system found on the surface of the erythrocytes of Rhesus monkey and human beings. In the blood it is inherited as a dominant trait.
(ii) An individual having D antigen are Rh D (Rh") and those without D antigen are Rh D negative (Rh).

A person with a recessive gene for haemophilia lacks a normal clotting substance (thromboplastin) in blood, hence minor injuries cause continuous bleeding, leading to death

Individuals have parts of their body expressing male characters and other parts of the body expressing female characters. The organism is made up of tissues of male and female genotypes and represents a mosaic pattern.

Mary Lyon suggested that Barr bodies represented an inactive chromosome, which in females becomes tightly coiled into a heterochromatin, a condensed and visible form of chromatin. The number of Barr bodies observed in cell was one less than the number of X-Chromosome. XO females have no Barr body, whereas XXY males have one Barr body.

Group of signs and symptoms that occur together and characterize a particular abnormality is called a syndrome. 
Eg : Down's syndrome, Turner's syndrome, Klinefelter's syndrome, Patau's syndrome are some of the examples of chromosomal disorders.

It is characterized by multiple and severe body malformations as well as profound mental deficiency. Small head with small eyes, cleft palate, malformation of the brain and internal organs are some of the symptoms of this syndrome.

(i) Sexual separation of the defectives.
(ii) Sterilization of the defectives
(iii) Control of immigration and
(iv) Regulation of marriages