@Artemisia Are you from a working class background, Artemisia?
I've experienced something like this and I think it has to do with the value 'society' places on the blue collar/white collar distinction and the attitudinal stance your blue collar-working relatives take towards this for the sake of their own egos (and I say this in a sympathetic way towards them).
My brother (who is 12 years older than me and with a different father) reacted dismissively or passively to my academic achievements because I think to him 'real work' is much more valuable. He's doing the same to his 16-year-old son now, trying to force him into his own trade rather than seeing the value of further education.
When I was younger, however, and gearing up for a career in the army, he was much more enthusiastic. I think it just had to do with his value system. Military service is ranked higher than academia, which is ranked nowhere.
My niece (who is the same age as me, because my sister had her young) also used to say things like 'just writing all day, that's easy', as if it isn't real work. She happens to have very underdeveloped writing skills. Now she is a very successful beautician and is a lot more supportive of my academics, because I think she's differentiated herself sufficiently.
I think jealousy is typically manifested in areas of deficiency rather than strength, until an area of strength is sufficiently well-developed to transform the jealousy into admiration.
For example, I admire people who are naturally social, whereas I might have been jealous of them in the past. Now I'm comfortable with socialising in my way (long & deep discussions with 1 friend at a time, typically), I don't see myself as 'deficient' and can admire people with much greater social skills with nothing but positive feelings towards them.
I think if someone sees themselves as deficient in one aspect, it makes sense to denigrate the value of that aspect in order to preserve the ego. This seems only to be necessary, however, if the ego is sufficiently fragile in the first place (as others have mentioned with examples).