A family name like Johansson means Johan's son (Johans son, in Swedish), and up to about a century ago these names actually told you who the person's father was. Then the genealogists don't call it a family name, but a patronymic (latin for father's name or something like that). For women, the corresponding patronymic would be Johansdotter, meaning Johan's daughter (Johans dotter, in Swedish). If, say, Nils Johansson got a son named Peter, the son was named Peter Nilsson—not Peter Johansson.
When the patronymics eventually turned into family names, the female form became very unusual. I've only seen a couple of cases where the female form is used in Sweden today. During the transition many women changed the ending of their patronymics from -dotter to -son, probably so that the name wouldn't sound oldfashioned. Vendela and her sisters have a father named Johan, but they seem to have called themselves Johansson rather than Johansdotter.
On Iceland, patronymics are still used by the majority of the population. They've modernized the custom a bit, though—today, you can use the matronymic instead of the patronymic if you like. Historically, a handful of Swedes with wealthy (or otherwise very important) mothers have used matronymics (we're talking Middle Ages or so now). By the way, another oddity of Icelandic names: They tend to use names pretty informally, hardly using titles at all and not using their patronymics (or matronymics or family names) nearly to the extent that Swedes or Americans use their family names. For this reason, their phone book is sorted alphabetically according to people's first name.
A couple of centuries ago, the spelling of names varied a lot. For instance, I've seen the name Vendela Adelaide with the spelling Vendela, Wendela, Vendla and Wendla, and Adelaide, Adelheid, Adelxeid, and Adeloid. In one record, her husband's name Peter was written Per instead, and so on. Obviously, there's no way we can know which spelling is correct, and maybe the people didn't care how their name was spelled as long as it sounded the same. Sometimes, the person entering information in the parish records misheard or mixed up similar names. Vendela's paternal grandfather is alternately called Petersson and Pehrsson, I'm not quite sure which spelling is correct but I think it's Petersson.
The Federation of Swedish Genealogical Societies recommend using a consistent, modern, spelling, and I try to do that. This means that i.e. an old letter from Sweden may be signed with a name that's spelled differently from when that name occurrs in the database. In the table below you can see a few examples of old spelling. The general recommendation is to use the modern spelling rather than the old one. In Swedish, 'W' is pronounced like 'V' and up to a century ago they seem to have been more or less interchangeable. Nowadays, 'V' has almost completely replaced 'W' and there's not a single word on 'W' in the Swedish dictionary, but the letter is often retained in family names. Also, there may be a silent 'H' in an old name (like in Adelheid above). These, too, are retained in some family names today, but they're otherwise not very frequent. I only know one single Swedish word that retains the spelling 'ch' for 'k'—it's the word och (=and).
|Old spelling||Pronounciation||Modern spelling|
|w or v||v||v|
|h||- (silent)||- (omitted)|
|c or ch||k||k|
|c (before soft vowel)||s||c|