Human Genetic Disorders
- The building blocks of heredity is genes, So the defects in the genes or genome called Genetic disorders.
- Transfer of characters from parents to offsprings called Heredity and also known as Inheritance.
- As a result, it passes from generation to generation.
- Genes have all the stored data, and information, to make up DNA and proteins.
- If any changes occur with this information is, then it leads to a genetic disorder.
- Any kind of sudden and an inheritable change in genes is Mutation.
- Mutant are those organisms who undergoes to mutation.
- Any substances or the agent which has the ability to cause mutation, therefore, called Mutagen.
Types of Genetic Disorders
- Genetic disorders are of two types –
- Mendelian Disorders
- Chromosomal Disorders
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Mendelian Genetic Disorders
- An alternation or Mutation in a single gene cause this disorders.
- Since childbirth, this conditions can found and it also predicted by the history of the family.
- These are rare disorders, therefore, it is found in only one person among the millions of people’s.
- Any of them can be inheritable or may not be or also sex-linked/autosomal-linked.
Here are some Mendelian Disorders –
- It’s a sex-linked recessive disorder, therefore, it passes generation to generation.
- Because of the defect in the blood coagulation process, the person continues to bleed even with a small injury.
- There are two types of Haemophilia – Haemophilia – A, and Haemophilia – B.
Haemophilia – A
- In this disease, the person is not able to synthesize AHG (antihemophilic globulin), which is required for blood clotting, therefore a small injury can be harmful.
- Also known as Bleeder’s disease.
- The genes of Haemophilia is located on X- Chromosomes. i.e., X(h)
- As we know, Female – XX, and Male – XY, So males suffer more than the females, because in males there is only one X- chromosome. Males – X(h)Y
- Mainly, females are carriers of this disease XX(h), but she will suffer from this only in the Homozygous condition X(h)X(h) when both the chromosome consist of the hemophilia gene.
- Queen Victoria was the carrier of hemophilia, So their male kids were suffered.
- The defective alleles produce non-functional proteins, which also affects the process of blood coagulation.
Haemophilia – B
- Also known as Christmas disease because of the absence of plasma thromboplastin.
- The absence of this factor is due to the mutation.
- Plasma thromboplastin is an important factor which is responsible for blood coagulation.
- This factor is produced naturally in the body and it’s also known as the Christmas factor because it was discovered by Stephen Christmas.
B. Sickle-cell anemia
- This disorder occurs due to the defect in the autosomal chromosome, therefore, it’s an autosome-linked recessive disorder.
- In this disorder, the shape of RBCs shape turns into sickles from the disk shape.
- This disorder can’t be cured.
- The normal RBCs cells are of disc shape and by which they can easily pass through the veins or even in the smallest blood vessels.
- But sickle cells are prolonged, rigid and sticky, So they can’t travel easily in the vessels by which they can’t reach the different part of the body. (blockage).
- As a result, it can cause tissue damage, pain or it can become a clot.
- Due to point mutation, glutamic acid got replace by valine at the sixth position of the β-Globin chain of the hemoglobin molecule.
- The mutant hemoglobin molecule undergoes polymerization under low oxygen tension causing the change in the shape of RBC from disk to elongated.
- It’s also an autosomal-linked receive disorder.
- Anemia is the main symptom of this genetic the disorder.
- It occurs due to the deletion or mutation, as a result, defect in the synthesis of one of the globin chains of hemoglobin.
- Due to this defect, the body is not able to produce RBCs or Haemoglobin.
- By which, the body doesn’t have enough amount of hemoglobin to carry oxygen to the each and every organ, as a result, you will feel fatigue.
- Thalassemia is of two type –
Alpha (α) – Thalassemia
- In this, the production of the α – globin chain is affected. So, the production of the β-Globin chain will increase and as a result, No. of the β-Globin chain > No. of the α-Globin chain
- Unstable Tetramers ( 4 monomers of β-Globin chain) will form and it has abnormal oxygen dissociation curves.
- It is controlled by the closely linked genes HBA1 and HBA2. These are two gene loci, So that means four alleles.( one gene loci = 2 allele). and they both are linked on Chromosome 16.
Beta ( β) – Thalassemia
- In this, the production of the β-Globin chain is affected. So, the production of the α-Globin chain will increase and as a result, No. of the α-Globin chain > No. of the β-Globin chain
- This occurs due to the mutations in the Chromosome 11’s HBB gene. In this mutation can occur in both of the genes or maybe the mutation of one gene.
- They don’t form Tetramers; rather, they produce damage to the cell membranes of RBCs because they get bind up with cell membranes of RBCs and membrane damage occurs.
Some Other Mendelian Genetic Disorders are:
Color blindness, Cystic Fibrosis, Phenylketonuria.
Chromosomal Genetic Disorders
- Due to excess, abnormal arrangements or absence of one or more chromones in a cell leads to chromosomal genetic disorders.
- During cell division, when chromatids fail to segregate properly from each other and as a result, it can be gain, loss or also abnormal arrangements in a chromosome. (Aneuploidy).
- Some types of chromosomal disorders pass generation to generation and some may not.
Here are some Mendelian Disorders –
A. Klinefelter Syndrome
- H. F. Klinefelter described this syndrome, in 1942.
- Karyotype of this syndrome is (44A+XXY). It occurs in Males.
Klinefelter symptoms are:
- The hair on their face and body is found to be similar to women.
- The testis is small in size and secondary sexual symptoms are similar to women because of one extra X chromosome.
- Breast size is large, as a result, of one extra X chromosome.
- The male suffering from this syndrome is sterile in a sexual manner due to the no. of chromosomes.
- Mental retardation because of the disturbance of chromosomes.
- Barr bodies are found in their cells, which can be one or more than one.
Klinefelter Syndrome https://bit.ly/2NOWDsN
B. Down’s Syndrome
- John Langdon Down first described Down syndrome, in 1866.
- Trisomy of chromosome 21, is the reason for this disorder.
- karyotype is “47, XY, +21
- There are two chromatids present in a single chromosome but due to abnormalities an addition of a single chromatid occurs, as a result, it becomes Trisomy.
Down’s Syndrome symptoms are:
- The affected person has a short-statured with small round head.
- They have the partially open mouth and also furrowed tongue.
- Slow mental development or Mental retardation.
- They have a broad palm with characteristic palm crease.
Down’s Syndrome https://bit.ly/2q1CYMB
. Turner’s Syndrome
- Dr. Henry Turner was the first who discovered this syndrome, in 1938.
- This syndrome occurs due to the absence of one of the X-Chromosome.
- Their karyotype is 45+XO.
- Due to abnormalities, there is a loss of one X chromosome.
- It occurs in females.
Turner’s syndrome symptoms:
- Females are sterile and also with rudimentary ovaries.
- Their neck is of webbed type.
- They don’t have fully developed breasts and their thorax is of shield-shaped.
- They have short stature, puffy fingers, and small uterus.
- Menstrual cycles are absent.
Turner’s Syndrome https://bit.ly/2NQFe2B