ASSIGNMENT NO 1 Genes are segments of DNA located on chromosomes

Genes are segments of DNA located on chromosomes. A gene mutation is defined as an alteration in the sequence of nucleotides in DNA. This change can affect a single nucleotide pair or larger gene segments of a chromosome. DNA consists of a polymer of nucleotides joined together. Altering nucleotide sequences most often results in nonfunctioning proteins. Mutations cause changes in the genetic code that lead to genetic variation and the potential to develop disease.

Point mutations are the most common type of gene mutation. Also called a base-pair substitution, this type of mutation changes a single nucleotide base pair. A point mutation is a type of mutation in DNA or RNA, the cell’s genetic material, in which one single nucleotide base is added, deleted or changed.

Point mutations can be categorized into three types:
Silent Mutation: Although a change in the DNA sequence occurs, this type of mutation does not change the protein that is to be produced.
Missense Mutation: This type of mutation alters the nucleotide sequence so that a different amino acid is produced.

Nonsense Mutation: This type of mutation alters the nucleotide sequence so that a stop codon is coded for in place of an amino acid.

Cystic Fibrosis (CF) is a recessive inherited disorder most common among people of European descent. There are many different mutations that can cause CF, but the most common one is a deletion of three nucleotides in the cystic fibrosis transmembrane conductance regulator (CFTR) gene that results in the loss of the amino acid phenylalanine and causes an incorrectly folded protein. (Note that this deletion is not a frameshift mutation because three bases next to each other are deleted, and all the other amino acids in the chain remain the same.) CF is associated with thick, sticky mucus in the lungs and trouble breathing, salty sweat, infertility in certain individuals, and a shortened life expectancy (about 42-50 years in developed countries).

Tay-Sachs disease is another recessive disorder caused by point mutations. Different mutations can cause this disorder, but they are all found on the HEXA gene on chromosome 15. Tay-Sachs causes nerve cells to deteriorate over time, which in turn results in the decline of physical and mental functioning. Both child and adult-onset forms of the disease occur. although the mutations associated with the disease are different in each population. There is currently no treatment or cure.

Wilson’s disease is a rare inherited disorder that causes copper to accumulate in your liver, brain and other vital organs. Most people with Wilson’s disease are diagnosed between the ages of 5 and 35.

Wilson’s disease is present at birth, but signs and symptoms don’t appear until the copper builds up in the brain, liver or other organ. Signs and symptoms vary depending on the parts of your body affected by the disease. They can include:
Fatigue, lack of appetite or abdominal pain
A yellowing of the skin and the whites of the eye (jaundice)
Golden-brown eye discoloration (Kayser-Fleischer rings)
Niemann-Pick disease (NPD) is a group of diseases passed down through families (inherited) in which fatty substances called lipids collect in the cells of the spleen, liver, and brain.There are 3 common forms of the disease:
Type A
Type B
Type C
Each type involves different organs. It may or may not involve the nervous system and breathing. Each one can cause different symptoms and may occur at different times throughout life.

Causes: NPD types A and B occur when cells in the body DO NOT have an enzyme called acid sphingomyelinase (ASM). This substance helps break down (metabolize) a fatty substance called sphingomyelin, which is found in every cell in the body.

TYROSINEMIATyrosinemia or tyrosinaemia is an error of metabolism, usually inborn, in which the body cannot effectively break down the amino acid tyrosine. Symptoms include liver and kidney disturbances and intellectual disability. Untreated, tyrosinemia can be fatal.Most inborn forms of tyrosinemia produce hypertyrosinemia (high levels of tyrosine).
Causes:Mutations in the FAH, TAT, or HPD gene cause a decrease in the activity of one of the enzymes in the breakdown of tyrosine.As a result, tyrosine and its byproducts accumulate to toxic levels, which can cause damage and death to cells in the liver, kidneys, nervous system, and other organs
Maple syrup urine disease (MSUD), also called branched-chain ketoaciduria, is an autosomal recessive1 metabolic disorder affecting branched-chain amino acids. It is one type of organic acidemia. The condition gets its name from the distinctive sweet odor of affected infants’ urine, particularly prior to diagnosis, and during times of acute illness.
Signs and symptoms: The disease is named for the presence of sweet-smelling urine, an odor similar to that of maple syrup, when the person goes into metabolic crisis. The smell is also present and sometimes stronger in the ear wax of an affected individual at these times. In populations to whom maple syrup is unfamiliar, the aroma can be likened to fenugreek, and fenugreek ingestion may impart the aroma to urine.

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