Two Brown-Eyed Parents, One Blue-Eyed Child
The Punnett square you learned at school is wrong about eye colour. Ciara explains the dozen or more genes involved, why recessive is not the whole story, and what this means for genetic risk.
What Your Ancestry Test Is Actually Measuring
0:00 / 0:41
This episode is for members. Sign up free or log in to hear the whole episode.
Show notes
The twelve percent problem
A listener from Cork took two ancestry tests and got two different answers. Ciara explains why that is normal. Consumer tests compare your DNA to reference groups of living people, not to historical populations, and the percentages shift whenever the reference panel grows. The episode also covers what the tests are genuinely good at, which is finding relatives.
- What a SNP chip reads and what it skips
- Reference panels and why Ireland is well covered but Nigeria is not
- Why percentages change between updates
- Relative matching and the surprises it causes
- The privacy questions to ask before you spit
Next week, eye colour and the myth of the single gene.
Transcript
Hello and welcome to Four Letters Long. I am Ciara Nolan, I am a geneticist in Dublin, and for eight years I read people's genomes and tried to explain them back. This show is that job, but with you. Today we start with a listener from Cork who took two ancestry tests and got two different pie charts. She wants to know which one is lying. The answer is neither, and the reason tells you a lot about what these tests actually measure, which is not history but a comparison to living people who happened to join the reference panel. I will explain what the chip reads, why the percentages shift, and the one thing these tests are brilliant at, which is finding relatives you did not know you had. You are listening on Witspeak Podcasts. Let us open the envelope.
Open as text