Hi Susan, and Welcome to Rootschat.
My parent has a half sibling ,which we knew nothing about until I uploaded my DNA .
To give you some idea on some real life examples - below is what my child and myself share with our half family. My parent hasn't tested ( but their half sibling and children have) , so I don't know what my parent's cms would be exactly against their half sibling of course ( the other siblings have passed away except my parent and their half sibling) , but me being the generation below, I test highly to my parent's half sibling, and am the next best thing to my own parent's dna of course.
( I've also added my 1st full cousin's , my parent's full sibling child's cms too ,at the bottom of the page under the Ps)
I share 1162cm with my parent's half sibling, which is on the higher end ( dna painter actually have a 7% chance that it could be a half sibling to me with this amount )
With their children (my 1st half cousins) I share 562 cm and 546cm
With my 1st half cousins child ( my half 1st cousin once removed) I share 290cm
My child :
shares 570 with my parent's half sibling (great to my child)
And 293 and 346cm with my 1st half cousins ( once removed half 1st to my child)
With my child's Second half cousin ( a child of the above 293cm cousin) my child shares 121cm
Hope this helps
I wish you all the best in locating your sister. Sometimes with the DNA route it is is very much a waiting game. More and more people are testing all the time . All it takes is a child, or grandchild ,or a great grandchild of your sister to test , if she has any of course.
That 400 to 450 cms falls well within a half great nephew/ niece ,an 85% chance at 450cm ( besides half first cousin and
first cousin once removed cousin - also a 13% chance of being a GG half nephew/ niece and so on ) ,My child who is a half great nephew of my parent's half sibling shares just a wee bit higher at 570cm.
Very Kind regards
Ps
My 1st full cousin shares 713cm to our parents half sibling ( where I share 1162)
And only shares 253 cm to our half 1st cousin ,where I share over 500cm with them ,and my child shares 293 and 346 cms with them.
My child actually shares more than my 1st full cousin does to our 1st half cousin.
At first glance people may mistakenly think my 1st full cousin could be on my child's generation line when comparing both of their cms to my 1st half cousins.
Given its only 13% chance on dna painter that 253cm is a half first cousin It's the way the cookie crumbles sometimes.
My advice would be , never overlook the lower cms ones in your matches , and overlook the lower percentage chances when using the calculators such as dna painter . Those lower cms and low percentage chances can be just as important.
I'd hate to guess what my 1st full cousin's children would be against our first half cousins if they were to test - they could very well be as low as 100cm, even less ( which would fall within 4% to 6% on dna painter ), given my full cousin is only 253 against them.
Kind regards.
