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How much DNA do we share?

The next time you refer to someone as monkeying around you may not be that far from the truth. Chimpanzees are our closest relative as a species and we share at least 98% of our genome with them. Our feline friends share 90% of homologous genes with us, with dogs it is 82%, 80% with cows, 69% with rats and 67% with mice [1].

Human and chimpanzee DNA is so similar because the two species are so closely related. They both descended from a single ancestor species 6 or 7,000,000 years ago. As they evolved, their DNA changed as it was passed from generation to generation. It is these DNA changes that account for the differences between human and chimp appearance and behaviour.

By virtue of being the same species, all humans share 99% of their genome, which means that all humans are 99% genetically similar.

Our bodies are made up of 3 billion genetic building blocks, or base pairs. Of those 3 billion base pairs, only a tiny amount are unique to us. The remaining 1% of genes that are different explain the variations in characteristics, such as colour of hair, eyes and skin, and also risk for certain diseases.

When undertaking a paternity test, DNA samples from family members are analysed. AlphaBiolabs examines short tandem repeat (STR) markers that are specific locations on chromosomes made up of sequences of repeated DNA. These STR markers are highly variable in length between individuals. Each individual has two copies of each STR marker, known as alleles: one is inherited from the father and the other from the mother. By looking at these specific DNA markers in each sample, it is possible to identify which half of the child’s DNA is inherited from the mother and which half is from the father.

AlphaBiolabs tests up to 35 STR markers including two sex markers when undertaking DNA testing. The two alleles observed at each STR marker are compared between the tested individuals.

When testing a biological parent, both child and the parent will share 50% of these identical sections of DNA at each marker. Identical twins share the same DNA profile. The average percentage of DNA shared for different types of relationships is shown in Table 1.

 

RelationshipAverage % DNA shared
Identical twin100%
Parent/child, full siblings50%
Grandparent/grandchild, aunt/uncle and niece/nephew, half siblings25%
First cousin12.5%

Table 1. Average DNA shared by pairs of relatives

 

A child’s entire genome is provided 50:50 by his or her parents (50% from the mother and 50% from the father). Our scientists look at the hypervariable regions of this DNA to see what was contributed by each parent.

For information on any of our DNA testing services, please contact AlphaBiolabs on 0333 600 1300; email: info@alphabiolabs.com; www.alphabiolabs.co.uk

[1] Initial sequence and comparative analysis of the cat genome. Genome Res 2007(17):1675–1689.

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