• Genetic disorder

Genetic disorder may be grouped into two categories-

1.mendilian disorder

2.chromosomal disorder

Mendilian disorder-:

Mendilian disorder are mainly determined by alteration or mutation in a single gene. These disorder are transmitted to the offspring on the same line as we have studied in the principle of inheritance. The pattern of inheritance of such mendilian disorder can be traced in a family by the pedigree analysis.Most common and prevalent mendilian disorder are haemophilia colour blindness sickle cell anemia phenylketourea thalassemia etc. It is important to mention here that such mendilian disorder may be dominant or recessive. By pedigree analysis one can easily understand weather the trait is quiet dominant or recessive.

Similarly the trait is also linked with sex chromosome as In case of haemophilia.

1. Colour blindness-:It’s sex linked recessive disorder due to defect in either red or green cone of eye resulting to failure discriminate between red and green colour.The is due to mutations of gene present on x chromosome.Due to which it occur about 8 % in male and 0.4 % In female.Male have only one ☓ chromosome and female have 2 X chromosome if women is carrier but his son is colorblind but in girl child the father is colour blind or women is colorblind.
2. Haemophilia-: The sex linked recessive disease which show it transmission from unaffected carrier female to some of the male progeny has been widely studied. In this diseases a single protein that is a part of the cascade of protein involved In the clotting of blood is affected due to this in an affected individual a simple cut will reasult in non stop bleeding. The heterozygous female carrier for haemophilia may transmit the diseases rare because mother of such a female has to be at least carrier and the father should be haemophilia. The family pedigree of queen Victoria show a number of haemophilia descendents as she was a carrier of the diseases.
3. Sickle cell anaemia-: This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene. This diseases is Controlled by a single pair of allele . Hb^a and Hb^s. Out of the three possibilities, genotype only homozygous individual for HB^s(hb^shb^s) show the Heterozygous individual appear Apparently unaffected But they are career of the disease as there is 50% probability of transmission of mutant gene to the progeny, thus exhibiting sickle cell trait. This defect is caused by Substitutions of glutamic acid by valine at the 6 position of the Beta global Chain of haemoglobin molecule. The substitution of amino acid in the protein result due to a single base substitution at the sixth cordon of Beta global Jean, from GAG to GUG. The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension, causing the change in shape of rbc.One from biconcave disc to elongated sickle like a structure.
4. Phenylketouria-: This Inborn error of metabolism is inherited as the Autosomal recessive trait. the affected individual lack an enzyme that convert the amino acid phenylalanine into tyrosine. As result of this phenylalanine is accumulated and converted into phenylpyruvicacid and other derivatives. accumulation of this in brain result in mental retardation. They are also excreted through urine because of its poor absorption by kidney.
5. Thalassemia-: This is also an Autosomal linked recessive Blood diseases transmitted from parents to the offspring. When both of the Partners are unaffected career for the gene or Heterozygous. the defect could be due to either mutations or deletion, which ultimately result in reduce rate of synthesis of one of the globin chain (alpha and beta)chain that make up haemoglobin. This causes the formation of abnormal haemoglobin molecule is affected resulting into anaemia , which is characteristic of the disease. Thalassemia can be classified according to which chain of the hemoglobin molecule is affected. In alpha Thalassemia the production of Alpha globlin Chain is affected while in Beta Thalassemia production of Beta globalin Chain is affected .Alpha. thalassemia is controlled by 2 closely linked Gene Hba 1even and Hba 2 on chromosome 16 of each parent and it is absorbed due to mutation or deletion of one or more of the four gene. the more gene affected, the less alpha globin molecule produced while Beta thalassemia is controlled by a single gene HbB on chromosome 11 of each parent and occurred due to mutations of one or more of the four gene. thalassemia differ from sickle cell anaemia, is that former is quantitative problem of synthesizing too few globin molecule.While the latter is qualitative problem of synthesizing incorrectly functioning globin.