Genetic Percentage If a half-brother married a lady and then his half-sister married the ladies brother, what is the genetic percentage that the children share? I know half-siblings share 25 percent and full siblings share 50 percent. Aunts and uncle's share 25 percent and half-uncle and half-aunts share 12.5. Would the children then share around 12.5 percent also?

The children would have:

* two parents that are brother and sister and who then share $50\%$ of genes;

* two parents that are half-brother and half-sister and who then share $25\%$ of genes.




Each of the four parents shares $50\%$ of genes with his/her own children. So the two children would share

$$0.5^2 (0.5+0.25)=18.75\%$$

Therefore, they would be genetically more similar than first cousins (who have two parents that are brothers/sisters and two other uncorrelated parents, resulting in $12.5\%$ gene sharing), but less similar than uncles-aunts/nephews-nieces or other half-siblings ($25\%$ sharing).