Guides for curious parents

Plain answers to the questions couples ask about genes and looks, with the sources behind them and a calculator where it helps.

When do babies' eyes change colour?
Many babies open their eyes grey or blue and end up with brown, green or hazel. Here is what happens in the first year, when the colour usually settles, and what the parents' eyes can tell you.
Will my baby's hair colour change?
The hair your baby is born with is rarely the hair they keep. Here is how it changes from the first weeks to the teenage years, and why.
Can two parents without red hair have a red-haired baby?
Yes, it happens, and it is not rare. Red hair comes from a version of one gene that can hide for generations. Here is how it works and how likely it is.
Can a baby have a different blood type from both parents?
Yes, and it happens all the time. Each parent can carry a hidden version of the blood group gene, so the baby's type can match neither of them.
Dimples, freckles, curly hair: which traits are dominant?
School biology says dimples and curly hair are dominant. The real picture is more interesting: most traits we can see depend on many genes at once.
Who will our baby look like?
Every baby gets half of their genes from each biological parent, yet many look more like one side. Here is why, what studies found, and why the answer changes as they grow.
Which traits come from each parent?
Some things really do come from one biological parent, such as the mitochondria. Many popular claims do not hold up. Here is what genetics actually says.
Do twins run in families?
Fraternal twins can run in families, through the parent who ovulates. Identical twins mostly happen by chance. Here is the difference and what changes the odds.
How accurate are AI baby generators?
An AI baby photo is a believable picture of a possible child, made for fun. It is not a genetic prediction. Here is what it can show, what it cannot, and how to get a better result.