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Do siblings have the same DNA or it can be different?

Do siblings have the same DNA or it can be different?

Not really. Here’s why your parents didn't make exact replicas and why siblings' DNA can be surprisingly different

Parents and Siblings

As biological siblings, two persons got their genes from their parents. Actually, there can be striking genetic differences between brothers and sisters. As National Geographic wrote, it happened that two twin girls were born with different skin colours: one child inherited the mother’s genes, and the other, the father’s.
That's why, even with the same parents, we only share some of our genes with our parents, which are about 50%. That's because the human body has several biological mechanisms that can create an almost infinite number of gene combinations. And this is what gives brothers and sisters different DNAs.

Different DNAs

DNA is packed into special units, called chromosomes. Scientists have numbered human chromosome pairs from 1 to 23 which allows them to locate and describe specific genes. Most cells are diploid, which means that they have two copies of each chromosome. One comes from mother, and the other from father, which adds up to a total of 46 chromosomes.

What is particularly interesting is the 23rd pair of chromosomes, since it is the one that defines biological sex. Girls (XX) inherit an X chromosome from both parents, but boys (XY) always get a Y instead of an X from their fathers.
Within a multicellular organism it is necessary that all cells (in order not to recognise each other as strangers) have the same hereditary heritage. This is provided by mitosis, dividing the chromosomes between the daughter cells, in which the equality of genetic information is ensured by the DNA reduplication mechanism, in a cellular continuity that goes from the zygote to the last cells of the organism, in what is called the somatic line of cell generations.

However, if the same mechanism were adopted in the generation of descendants, the whole species would tend to be composed of genetically equal individuals. Such a lack of genetic variability could easily affect the survival of the species as environmental conditions change. Therefore it is necessary that the species, within the variability of the genetic material that it admits, can give rise to a reassortment, a mixing, not within the individual organism, but in the passage from one generation to another. This is done by the phenomena of sexuality and the particular mechanism of cell division called meiosis (meiosis is a form of cell division that is only used to produce a special category of cells, called gametes. Depending on your biological sex, your body produces one type of gametes: either sperm or egg cells).

How much DNA from each parent?

Every child gets 50% of their genome from each parent, but it is always a different 50%. During meiosis, gametes get a random chromosome from each pair. This means that there are over 8 million possible DNA combinations from 23 chromosome sets!  

However, nature has another mechanism to further differentiate brother and sister DNA. Scientists find similar and different genes in siblings, often even on the same chromosome: this mix-up is possible because of a biological mechanism called chromosomal crossover during meiosis. 

The genes transferred from one chromosome end up in the same location on the other chromosome. Because of this swap, gametes receive a unique jigsaw puzzle assembled from the two original sources. This generates even more diversity between sibling DNA.

Every gene is made up from thousands of one-letter DNA blocks: adenine (A), thymine (T), guanine (G), and cytosine (C). Our cells use these sequences as blueprints to produce proteins - molecular machines with specialised functions.

99% of DNA is the same for all people, otherwise the blueprints wouldn’t work. However, a single-letter change in certain genes doesn’t change the protein recipe too much. These alterations are called single nucleotide polymorphisms (SNPs).

It doesn’t matter which family you are from, DNA is surprisingly different!

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