In some families all children are the same sex. Give the reason why. [1 mark]

Data from the Medical Birth Registry of Norway, covering more than 540,000 women with two, three and four births for the period 1967-2003, were used to study how the sex distributions of children already born affected the probability of a new birth and the sex of the next sibling.

Results: Women with two children of the same sex had a higher probability of having more children compared to women with two children of both sexes (RR=1.14, (1.14-1.15)). This also applied to mothers with three children (RR=1.15 (1.13-1.17)). The probability was highest for mothers with boys only. Multiple births and parity affected the probability of giving birth to a boy versus a girl, but the sex composition of already born siblings had no influence.

Explanation:

Government of norway has this on their site!

Check below for proof

https://pubmed.ncbi.nlm.nih.gov/16357880/

they have sperm in my gf's mouth

explanation: