I have a sister and we have a 5 year age gap. To cut a long story short it has taken about 20 years for us to be friends - I don't think gender is always the issue to be honest I think age gaps contribute more to sibling animosit, at least this is the case in my experience. We just never had anything in common as the age gap felt huge when I was 10, 15, 20 etc. Weirdly I have always wanted a brother and have lots of male friends (and female ones)maybe trying to fill that gap. I am now pregnant and find myself being a little scared about having a boy as I have no experience of growing up with a brother. Your experience is unique to you and I understand your apprehension but I think every sibing relationship is completely different and is subject to so many factors, Congrats on your pregnancy!