99% of DNA sequences are conserved among humans, the remaining 1% makes you unique!
Your genetic information is inherited from both your parents: 50% from your mother and 50% from your father.
DNA are Life’s blueprints and contain hereditary information determining all your personal traits including: height, body part pigmentation (hair, eye, skin) and likelihood of developing health problems. More specifically, your genes or small DNA segments are packaged into “DNA bundles” called chromosomes – humans have 23 chromosome pairs.
We have two copies of each gene, one on each chromosome, which can come in different versions called alleles. While the same gene is responsible for eye colour, the allelic combination defines the eye colour (green, blue, hazelnut etc). Therefore, genetic differences explain why we are physically different to our peers. Variants or mutations different to the expected genetic sequence also arise frequently. Rest assured, not all are harmful, but some can increase likelihood of certain diseases.
Genetics is a biology branch which studies how human traits are determined and how they are passed down generations. Many genes contain information for protein synthesis which are important in building cells, muscle movement and food digestion. If important genes coding for proteins are mutated, this will affect the normal protein function leading to genetic diseases:
Autosomal dominant diseases: one out of the two allele copies of the gene is altered and enough to cause the disease. For example, if a person contains a single altered copy of the HTT gene, this causes Huntington disease – a progressive brain disorder leading to uncontrolled movements, emotional instability, and logical thinking loss.
Autosomal recessive diseases: both alleles copies of the gene are mutated to cause the disease. Cystic Fibrosis, characterised by breathing difficulties and frequent lung infections, results from mutation in both copies of the CFTR gene.
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X-linked diseases: Sex chromosomes determine gender- a female is XX while a male is XY.
As males have a single X chromosome, they are more likely to develop a X-linked disease. Females naturally and randomly “shut down” the expression of one of two X gene copies, so if they inactivate the altered gene, they will be unaffected by the disease but remain a carrier. Carriers, contain one mutated gene copy and if their partner also contains the same mutation then their children will have the disease, even though the parents do not. Red-green colour blindness is an example of an X-linked recessive disease, more prominent amongst men.
It gets more complex when multiple mutated genes are responsible for the same disease and when environmental factors (diet, exercise frequency, lifestyle) come into play. Indeed, asthma, diabetes and Alzheimer’s disease are complex disorders with no clear-cut pattern of inheritance which make them more challenging to study and treat. Despite this, genomic medicine aims to develop new disease diagnostic tools and develop personalised drugs to target mutations.