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Haemophilia, Haemophilia is a sex linked recessive disease, which shows transmission from, unaffected carrier female to some of the male progenies. In this disease, a single, protein involved in the clotting of blood is affected. Due to this, in an affected, individual a simple cut will result in non-stop bleeding., The heterozygous female (carrier) for haemophilia may transmit the disease to sons., The possibility of a female becoming a haemophilic is extremely rare because, mother of such a female has to be at least carrier and the father should be, , haemophilic., Phenylketonuria, Phenylketonuria, an inborn error of metabolism is also inherited as the autosomal, recessive trait., T h e affected individual lacks an enzyme that converts the amino acid phenylalanine, into tyrosine. As a result of this phenylalanine is accumulated and converted into, phenylpyruvic acid and other derivatives. Accumulation of these in brain results in, mental retardation. These are also excreted through urine because of its poor, , absorption by kidney., Thalassemia, It is an autosome linked recessive blood disease transmitted from parents to the, offspring when both the parents are unaffected carriers for the gene. The defect, could be due to either mutation or deletion which ultimately results in reduced rate

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of synthesis of one of the globin chains (a and B chains) that make up haemoglobin., This cause the formation of abnormal haemoglobin molecules resulting into anaemia, which is characteristic of the disease., Depending upon the globin chain affected, thalassemia is of three types - a, B and 6., , a. a-thalassemia- Caused by defective formation of a-globin, controlled by two, genes HBA1 and HBA2, Present on chromosome 16., b., , B-thalassemia - Decreased synthesis of B-globin. Defect is due to alleles of HBB, , genes present on chromosome 11., C. 6-thalassemia- It occurs due to defective allele of HBD gene present on, chromosome 11., Colour blindness, Colour blindness is a sex linked recessive disorder due to defect in either red or, green cone of eye resulting in failure to discriminate between red and green colour., This defect is due to mutation in certain genes present in the X-chromosome., , Colourblind female is X X, X Xis carrier female, XC Yis affected male., Chromosomal disorders, The chromosomal disorders are caused due to absence or excess or abnormal, arrangement of chromosomes., Failure of segregation of chromatids during cell division cycle results in the gain or, loss of a chromosome(s), called Aneuploidy. For example, Down's syndrome results, in the gain of extra copy of chromosome 21. Turner's syndrome results due to loss of, an X chromosome in human females., Polyploidy is a phenomenon of failure of cytokinesis after telophase stage of cell, division resulting in an increase in a whole set of chromosomes in an organism., The total number of chromosomes in a normal human cell is 46 (23 pairs). 22 pairs, are autosomes and one pair of sex chromosome., Sometimes, though rarely, either an additional copy ofa chromosome may be, included in an individual or an individual may lack one of any one pair of, chromosomes. These situations are known as trisomy or monosomy of a, chromosome, respectively. Such a situation leads to very serious consequences in, the individual., , Some chromosomal abnormalities, 1. Down's syndrome, , Karyotype-, , Trisomy 21, , Main clinical features-Short, broad palm with characteristic palmer crease,, decreased muscle tone, mental retardation, small round head, partially open mouth, with furrowed tongue.

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2. Edward's syndrome, , Karyotype- Trisomy 18, Main clinical features-Multiple congenital malformation of many organs, receding, mandible, small mouth and nose, severe mental deficiency, fingers tightly clenched, against palms of hands., , 3. Turner's syndrome, , Karyotype- 45, XO, Main clinical features - Female with retarded sexual development, usually sterile as, ovaries are rudimentary, short stature, webbed neck, cardiovascular abnormalities, and hearing impairment., , 4. Klinefelter's syndrome, , Karyotype- 47, XXY, Main clinical features Sterile male with small testes, may have some breast, development, tall, mild mental deficiency, long limbs.