Final answer:
An autosomal dominant gene is a gene that needs to be present in only one parent to have a 50-50 chance of affecting each child.
Step-by-step explanation:
In genetics, a gene that needs to be present in only one parent to have a 50-50 chance of affecting each child is called an autosomal dominant gene. This means that if one parent has the gene, there is a 50% chance that it will be passed on to the child.
For example, let's consider a trait like dimples. If the gene for dimples is dominant, a child will have a 50% chance of inheriting the gene and developing dimples if only one parent has the gene.
However, if both parents have the gene, the chances of the child inheriting the gene and developing the trait increase to 75%, because the child will inherit the gene from both parents.