Why grandmothers prefer their son's daughters

The study, published in the journal Proceedings of the Royal Society B, found that a grandmother's love for her grandchildren is partially rooted in DNA.
The Cambridge University scientists concluded that a grandmother shares most genes with her son's daughters – and the least with her son's sons.

Applied to the Royal family, it would mean that Prince Andrew's daughter's, Beatrice and Eugenie, should find it easier to please the Queen than Charles's sons William and Harry.
And as sons of a son, the two princes should be among her least favourite grandchildren.
The researchers first used the laws of inheritance to work out how genetically similar a woman is to her children's children and found that overall, a grandmother and grandchild share around a quarter of their genes.

But differences in the way the genes on the X chromosome are passed through the generations mean that some grandchildren share more than this.
A woman passes around 31 per cent of her genes to her son's daughters but just 23 per cent to her son's sons. Her daughter's children fall in the middle, with both sexes sharing around 25 per cent of their genes.

The data was drawn from seven societies across the world and from the 17th to the 21st centuries.

Writing in the journal Proceedings of the Royal Society B, the researchers said: "Our sex-specific analysis shows that paternal grandmothers have a consistent opposite effect on boys and girls."

They add that a child may give off "signals" that make it easy for grandmothers to work out how close they are genetically. The clues may be in smell form, or may be as simple as facial resemblance.