(a) Genetic Disorders:
1. These are disorders (or) illness caused by one or more abnormalities in the autosomes or sex chromosomes of the person.
2. This is referred to as autosomal disorder (or) sex-linked disorders, respectively.
3. They are divided as on the basis of dominant and recessive features as.
(i) Autosomal dominant- (e.g) Huntington's chorea
(ii) Autosomal recessive - (e.g.) sickle cell anaemia thalassima
(iii) Sex-linked abnormalities - (e.g.) Defective tooth enamel
(iv) Sex-linked recessive - (e.g) Colour blindness, haemophilia, etc
(c) (i) Haemophilia:
(i) Commonly known as bleeder's disease.
(ii) More common in men than women.
(iii) Hereditary disease.
(iv) Firstly reported by John Cotto in 1803.
(v) Caused by a recessive X-linked gene.
(vi) Suffers lacks a normal clotting substance (thromboplastin) in blood.
(vii) Hence minor injuries cause continuous bleeding, leading to death.
(viii) The females are always carriers.
(x) Females would transmit the disease to 50% of their sons even if the male parent is normal.
(xi) Follows the characteristic criss - cross pattern of inheritance.
(iii) Colour blindness:
(i) In human beings a dominant X - linked gene is necessary for the formation of colour sensitive cells, the cones.
(ii) The recessive form of this gene is incapable of producing colour sensitive cone cells.
(iii) Homozygous recessive females (X^cX^c) and hemizygous recessive males (X^cY) are unable to distinguish red and green colour.
(iii) Huntington's chorea:
(i) A hereditory disease which is inherited as an autosomal dominant lethal gene in man.
(ii) It is characterized by involuntary jerking of the body and progressive degeneration of the nervous system, accompanied by gradual mental and physical deteriorations.
(iii) The patients with this disease usually die between the age of 35 and 40.

The genotypes of parents are

(i) 50% daughter are normal visioned.
(ii) 50% will be carrier.
(iii) 50% of sons are likely to be colour blind.
(iv) 50% are normal visioned.

Chromosomal Abnormalities:
(a) Down syndrome is an autosomal disorder that is caused by the trisomy of chromosome 21 (repetition of copy of 21^th body chromosomes). It is characterised by
(i) Severe mental retardation
(ii) Defective development of the central nervous system
(iii) Increased separation between the eyes
(iv) Flattened nose, ears are malformed,
(v) Mouth is constantly open
(vi) Protrudes tongue
(b) Klinefelters Syndrome: (XXY males)
(i) It is the chromosomal disorder that is caused by the presence of an additional copy of the X chromosome resulting in a karyotype of 45 + XXY.
(ii) In this disorder sex of individual is masculine but posses feminine character also. Individual shows gynaecomastia i.e developed of breasts of males.
(c) Turner's Syndrome: (XO females)
(i) It is the chromosomal disorder that is caused by the absence of one of X-chromosomes resulting in the karyotype 45 + XO 
(ii) Persons with his syndrome have 45 chromosomes (44 autosomes and one X chromosome) (44 AA+ XO)
(iii) Low stature, webbed neck, under developed brest, rudimentary gonads lack of menstrual cycle during puberty are the main symptoms of this syndrome.

Mendelian disorder	Chromosomal disorder
(i) It is due to alteration (or) mutation in a single gene	(i) Chromosomal disorders are those caused due to absence (or) excess number of one or more chromosome(s)or abnormal arrangement of one/more chromosomes.
(ii) Such charges are transmitted to the progeny in the same way as the Mendelian pattern of inheritance	(ii) Such charges transmitted as the affected individuals is sterile
(iii) The pattern (or) inheritance can be traced in a family tree by pedigree analysis	(iii) The disease can be confirmed by karyotyping
(iv) Eg. Phenylketonuria colour blindness	(iv) Eg: Down syndrome, Turner's syndrome

 

(i) Rh incompatibility has great significance in child birth.
(ii) If a woman is Rh negative and the man is Rh positive, the foetus may be Rh positive having inherited the factor from its father.
(iii) The Rh negative mother becomes sensitized by carrying Rh positive foetus within her body,
(iv) Due to damage of blood vessels, during child birth, the mother's immune system recognizes the Rh antigens and gets sensitized.
(v) The sensitized mother produces Rh antibodies.
(vi) The antibodies are IgG type which are small and can cross placenta and enter the foetal circulation.
(vii) By the time the mother gets sensitized, and produce anti'D' antibodies, the child is delivered.
(viii) Usually no effects are associated with exposure of the mother to Rh positive mild antigens during the first child birth
(x) Subsequent Rh positive children carried by the same mother, may be exposed to antibodies produced by the mother against Rh antigen, which are carried across the placenta into the foetal blood circulation
(xi) This causes haemolysis of foetal RBCs resulting in haemolytic jaundice and anaemia due to wild antigens.
(xii) This condition is known as Erythoblastosis foetalis or Haemolytic disease of the new born (HDN).

(i) A chromosomal abnormality is a genetic disorder that occurs when there is a change in the number or structure of chromosomes. Chromosomes are carriers of genetic information, and a normal human cell has 23 pairs of chromosomes, or 46 chromosomes total. Chromosomal abnormalities can affect autosomes, sex chromosomes, or both.
(ii) Two examples of autosomal aneuploidies in humans are trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome):
Trisomy 21 (Down syndrome)
This is the most common autosomal aneuploidy in infants and affects about 1 in 800 births. It's associated with high rates of morbidity and mortality, but people with Down syndrome can live to be about 50 years old.
Trisomy 18 (Edwards syndrome)
This aneuploidy affects about 1 in 6,000 births. Fetuses with trisomy 18 survive to term but are only viable for weeks or months. 
Most aneuploidies that affect autosomal chromosomes are incompatible with life and often result in spontaneous abortions in the first few weeks of pregnancy.

In human beings a dominant X - linked gene is necessary for the formation of colour sensitive cells, the cones. The recessive form of this gene is incapable of producing colour sensitive cone cells. Homozygous recessive females (XCXC) and hemizygous recessive males (X'Y) are unable to distinguish red and green colour. The inheritance of colour blindness can be studied in the following two types of marriages.
Marriage between colour blind man and normal visioned woman:
(i) A marriage between a colour blind man and a normal visioned woman will produce normal visioned male and female individuals in F1 generation but the females are carriers.
(ii) The marriage between a F1 normal visioned carrier woman and a normal visioned male will produce one normal visioned female, one carrier female, one normal visioned male and one colour blind male' in F2 generation ..
(iii) Colour blind trait is inherited from the male parent to his grandson. through carrier daughter, which is an example of criss-cross pattern of inheritance.

(a) Thalassemia
Thalassemia is an autosomal recessive disorder. It is caused by gene mutation resulting in excessive destruction of RBC's due to the formation of abnormal hemoglobin molecules. Normally haemoglobin is composed of four polypeptide chains, two alpha, and two beta globin chains. Thalassemia patients have defects in either the alpha or beta globin chain causing the production of abnormal haemoglobin molecules resulting in anaemia.
Thalassemia is classified into alpha and beta based on which chain of haemoglobin molecule is affected. It is controlled by two closely linked genes HBA1 and HBA2 on chromosome 16. Mutation or deletion of one or more of the four alpha gene alleles causes Alpha Thalassemia. In Beta Thalassemia, production of beta globin chain is affected. It is controlled by a single gene (RBB) on chromosome 11. It is the most common type of Thalassemia and is also known as Cooley's anaemia. In this disorder, the alpha chain production is increased and damages the membranes of RBC.
(b) Albinism
Albinism is an inborn error of metabolism, caused due to an autosomal recessive gene. Melanin pigment is responsible for skin colour. Absence of melanin results in a condition called albinism. A person with the recessive allele lacks the tyrosinase enzyme system, which is required for the conversion of dihydroxyphenyl alanine (DOPA) into melanin pigment inside the me1anocytes. In an albino, melanocytes are present in normal numbers in their skin, hair, iris, etc., but lack melanin pigment.
 3, 4 - dihydroxy phenylalanine (DOPA) \(\underrightarrow { Tyrosinase } \)  Melanin

Rh incompatability has great significance in childbirth. If a woman is Rh negative and the man is Rh positive, the foetus may be Rh positive having inherited the factor from its father. The Rh negative mother becomes sensitized by carrying Rh-positive foetus within her body. Due to damage of blood vessels, during childbirth, the mother's immune system recognizes the Rh antigens and gets sensitized. The sensitized mother produces Rh antibodies. The antibodies are IgG type which are small and can cross placenta and enter the foetal circulation. By the time the mother gets sensitized and produce anti 'D' antibodies, the child is delivered.
Usually, no effects are associated with exposure of the mother to Rh positive antigen during· the first childbirth, subsequent Rh positive children carried by the same mother may be exposed to antibodies produced by the mother against Rh antigen, which are carried across the placenta into the foetal blood circulation. This causes haemolysis of foetal RBCs resulting in haemolytic jaundice and anaemia. This condition is known as Erythroblastosis foetalis or Haemolytic disease of the newborn (HDN).

In human beings the diploid (2n) body cell has 46 chromosomes (23 pairs).
i) chromosomal abnormalities are caused by errors is the number or structure of chromosome.
ii) Failure of chromatids to segregate during cell division resulting in the gain or loss of of one or more choromosomes called aneuploidy. It is caused by the nondisjunction of chromosomes.
iii) There abnormalities causes various syndromes in human beings. They are

1. Down's Syndrome/ Trisomy-21:
Trisomic condition of chromosome - 21 
Symptoms :
(i) severe mental retardation,
(ii) Defective development of the central nervous system,
(iii) increased separation between the eyes,
(iv) flattened nose, ears are malformed,
(v) mouth is constantly open and the tongue protrudes.
2. Patau's Syndrome/ Trisomy-13
i) Trisomic condition of chromosome l3 results in Patau's syndrome.
ii) Meiotic non disjunction is thought to be the cause for this chromosomal abnormality.
ii) It is characterized by
symptoms
(i) multiple and severe body malformations as well as profound mental deficiency.
(ii) Small head with small eyes,
(iii) cleft palate,
(iv) malformation of the brain
(v) internal organs 
b. Allosomal abnormalities is human beings:
Mitotic or meiotic non-disjunction of sex chromosomes causes allosomal abnormalities. Several sex chromosomal abnormalities have been detected. Eg. Klinefelter's syndrome and Turner's syndrome.
1. Klineletter's Syndrome(XXY Males):
(i) It is due to the presence of an additional copy of the X chromosome resulting in a karyotype of 47, XXY.
(ii) Persons with this syndrome have 47 chromosomes (44AA+XXY).
symptoms
sterile males, tall, obese, with long limbs, high pitched voice, under developed genitalia and have feeble breast (gynaecomastia) development.
2. Turner's Syndrome (XO Females):
(i) It is due to the loss of a X chromosome resulting in a karyotype of 45, X.
(ii) Persons with this syndrome have 45 chromosomes (44 autosomes and one X chromosome) (44AA + XO) and are sterile females.
symptoms
Low stature, webbed neck, under developed breast, rudimentary gonads lack of menstrual cycle during puberty, are the main symptoms of this syndrome.

The Mendelian disorders in human beings are
(a) Thalassemia
(b) Sickle cell anaemia
(c) Huntington chorea
(d) Phenylketonuria
(e) Albinism
(a) Thalassemia
(i) Thalassemia is an autosomal recessive disorder. It is caused by gene mutation resulting in excessive destruction of RBC's due to the formation of abnormal haemoglobin molecules.
Normally haemoglobin is composed of four polypeptide chains, two alpha and two beta globin chains.
(ii) Thalassemia patients have defects in either the alpha or beta globin chain causing the production of abnormal haemoglobin molecules resulting in anaemia.
Classified based on heaemoglobin
Alpha Thalassemia:
(i) Mutation or deletion of one or more of the four alpha gene alleles.
(ii) It is controlled by two closely linked genes HBAI and HBA2 on chromosome 16.
Beta Thalassemia:
(i) Production of beta globin chain is affected
(ii) It is controlled by a single gene (HBB) on chromosome 11.
(iii) It's is also known as Cocley's anemia.
(iv) It increases the alpha chain production and damages the membranes of RBC.
Huntington's chorea:
(i) It is inherited as an autosomal dominant lethal gene in man.
(ii) It is characterized by involuntary jerking of the body and progressive degeneration of the nervous system, accompanied by gradual mental and physical deterioration.
(iii) The patients with this disease usually die between the age of 35 and 40.

The methods adopted for the improvement of human beings are
(i) Eugenics
(ii) Euthenics
(iii) Euphenics
Eugenics:
Application of the laws of genetics for the improvement of human race is called eugenics. The term eugenics means "well born" and was coined by Francis Galton in 1885. For the betterment of future generations it is necessary to increase the population of outstanding people and to decrease the population of abnormal and defective people by applying the principles of eugenics.
Two methods of Eugenics
(i) Constructive method or Positive eugenics
(ii) Restrictive method or Negative eugenics
(i) Positive eugenics: Positive eugenics attempts to increase consistently better or desirable germplasm and to preserve the best germplasm of the society. The desirable traits can be increased by adopting the following measures:
a) Early marriage of those having desirable traits
b) Subsiding the fit and establishing sperm and egg banks of precious germplasm 
c) Educating the basic principles of genetics and eugenics
d) Improvement of environmental conditions
e) Promotion of genetic research
(ii) Negative eugenics: Negative Eugenics attempts to eliminate the defective germplasm of the society by adopting the following measures:
(a) Sexual separation of the defectives
(b) Sterilization of the defectives
(c) Control of immigration and
(d) Regulation of marriages
Euphenics:
man is called Euphenics or Medical engineering. In 1960, Joshua Lederberg coined the term Euphenics. It means normal appearing. It deals with the control of several inherited human diseases especially the inborn errors of metabolism. Eg. Phenylketonuria (PKU)
Euthenics:
The science of improvement of existing human race by improving the environmental conditions is called euthenics. It can be achieved by subjecting them to better nutrition, better unpolluted ecological conditions, better education and sufficient medical facilities

Mitotic or meiotic non-disjunction of sex chromosomes causes allosomal abnormalities. Several sex chromosomal abnormalities have been detected. Eg. Klinefelter's syndrome and Turner's syndrome.
i) Klinefelter's Syndrome (XXY Males)
This genetic disorder is due to the presence of an additional copy of the X chromosome resulting in a karyotype of 47,XXY. Persons with this syndrome have 47 chromosomes (44AA+XXY). They are usually sterile males, tall, obese, with long limbs, high pitched voice, under developed genitalia and have feeble breast (gynecomastia) development.
(ii) Turner's Syndrome (XO Females)
This genetic disorder is due to the loss of a X chromosome resulting in a karyotype of 45, X. Persons with this syndrome have 45 chromosomes (44 auto somes and one X chromosome) (44AA+XO) and are sterile females. Low stature, webbed neck, under developed breast, rudimentary gonads lack of menstrual cycle during puberty, are the main symptoms of this syndrome.

(i) Thalassemia is an autosomal recessive disorder. It is caused by gene mutation resulting in excessive destruction of RBC's due to the formation of abnormal haemoglobin molecules. Normally haemoglobin is composed of four polypeptide chains, two ph and two bet globin chains. Thalassemia patients have defects in either the alpha or beta globin chain causing the production of abnormal haemoglobin molecules resulting in anaemia.
(ii) Thalassemia. is classified into alpha and beta based on which chain of haemoglobin molecule is affected. It is controlled by two closely linked genes HBAI and HBA2 on chromosome 16.Mutation or deletion of one or more of the four alpha gene alleles causes Alpha Thalassemia. In Beta Thalassemia, production of beta globin chain is affected. It is controlled by a single gene (HBB) on chromosome 11. It is the most common type of Thalassemia and is also known as Cooley's anaemia. In this disorder the alpha chain production is increased and damages the membranes of RBC

In human beings a dominant X - linked gene is necessary for the formation of colour sensitive cells, the cones. The recessive form of this gene is incapable of producing colour sensitive cone cells. Homozygous recessive females (X^cX^c) and hemizygous recessive males (X^cY) are unable to distinguish red and green colour. The inheritance of colour blindness can be studied in the following two types of marriages.
(i) Marriage between colour blind man and normal visioned woman:
A marriage between a colour blind man and a normal visioned woman will produce normal visioned male and female individuals in Fl generation but the females are carriers. The marriage between a Fl normal visioned carrier woman and a normal visioned male will produce one normal visioned female, one carrier female, one normal visioned male and one colour blind male. Colour blind trait is inherited from the male parent to his grandson through carrier daughter, which is an example of criss-cross pattern of inheritance.

(ii) Marriage between normal visioned man and colour blind woman:
a) If a colour blind woman (X^CX^C) marries a normal visioned male (X^Cy), all F₁ sons will be colourblind and daughters will be normal visioned but are carriers.
b) Marriage between F₁ carrier female with a colour blind male will produce normal visioned carrier daughter, colourblind daughter, normal visioned son and a colourblind son in the F₂ generation.