.
The sample size for the uk sylhetis may have been small, it's not like I'm saying every single sylheti has arab origins or anything, my sylheti father himself is pretty dark coming from a poor family in Moulvibazaar; I for sure know he's got your typical bangla genetic composition. My mom occasionally teases him about his complexion lol. On my paternal side I have sylheti cousins that are dark as Tamils, caramel skin with mongoloid features, as well as a couple of cousins that look persian. The one that looks persian, their mom(my chachi) is a uk sylehti who also looks persian. So yeah a lot of diversity exists indeed.
As far as the family book, I'll have to ask my mom about how far back the book goes.
Let me explain it in details. Traits like facial feature, skin tone ect. are influenced by a small numbers of gene. So there are many phenotypes within a single "mixed" ethnic group. Since Bengali race was formed by 3 distinctive early human races, our traits are also more diverse.
Now take a look on how Bengali race was formed based on early Eurasians DNA, I hope you read those papers I posted before:
- 50% of genes belongs to early agriculturalist that migrated from fertile crescent, possibly modern day Iran. They are closely related to west Asians, Caucasians, Arabs and Europeans.
-20-25% of genes belongs to aboriginal ancestral south Asians. They are distantly related to Melanesians or Papuans.
-10-15% of genes belongs to proto Indo Europeans from Sinthasta,Andronovo,Yamnaya cultures. They are also closely related to Europeans,West Asians ect.
-10-15% of genes belongs to East Asians of both Tibeoto Burman and Austroasiatic family.
Now let's see how the genes influence our traits, since you are more interested to know why your dad and mom looks so different.
First of all, let's suppose your mom is a descendent of shah Jalal's companion, but we know that they came to Bengal in 1300, or 21 generation back. If the second generation of those Arab-Sylhetis had 50% Bengali genes(from their moms), the third generation was 25% Arab, fourth generation was 12,5% arab ect. so in modern time a direct descendent of those Arabs would score only traces of arab/yemeni genes, around 2-3% at best. Ive seen an Indian muslim of Yemeni origin(He has arab Y dna E1b), scoring only 3% Arab in DNA scores.
Traits are also affected by genetic selection, for example Partent-A is dark skinned and tall and Parent-B is light skinned and short. They have 3 kids, Kid-A got light skin tone from Parent-B and tall stature from Parent-A, Kid-B got dark skin tone from Parent-A and medium height(average height of P-A and P-B) and Kid-C got medium skin and short height. I know a mixed girl(half Italain and half Nigerian), she looks fully black African, people always tell to her Italian mom if she was adopted lol.
The same happenes with Bengalis, look at Bidya Sinha Mim's family, She's hindu so there is no chance of any Arab genes on her. Her caste is Saha, I think it is some sort of middle caste or lower-middle caste in Hindu caste system.
She(Mim) looks heavily influenced by those early agriculturalist genes that Bengalis have. Her sister on the other hand looks moderately east Asian influenced, her mom and dad look balanced mix with her mom being a bit more in the east Asian and early agriculturalist side and her dad being in both east Asian and Ancestral south Asian side. Hindus are very endogamous society, so genetically both her mom and dad would be the same.
Anyway you are always free to take a DNA test, but im very much confident it will be 99% local Bengali.