How to work out my great-grandmother's father?

[1931census]

(Names edited for privacy)

My great-grandmother 'Jane' was born illegitimately in London in 1919. She did not know her father ('X'), but was told by her mother that he was a Jewish man. This was proven true when my mother (X's great-granddaughter) took a DNA test and was 15% European Jewish (this absolutely cannot have come from anywhere else in her family).

I believe that I have narrowed Jane's father down to one of six brothers (1, 2, 3, 4, 5 and 6), with the surname 'Katz', who were the sons of Polish Jewish immigrants and were in the right place at the right time (and were appropriate ages: there were two more brothers that I excluded as they were underage). When they are compared to my mother's matches that I know the identity of:

'Jack Katz' shares 249cM of DNA with my mother and is the grandson of Brother 1
'Peter Zielinski' shares 123cM of DNA with my mother and is the great-grandson of Brother 1
'George Katz' shares 69cM of DNA with my mother and is the son of the Katz brothers' cousin
'Gerald Katz' shares 61cM of DNA with my mother and is the son of 'George Katz'
'Lewis Smith' shares 29cM of DNA with my mother and the great-grandson of Brother 1

These are the only people that replied to my messages/ knew about their family tree. Obviously, Brother 1 comes up the most here. How likely is it that he was Jane's father?

[Rena]

female given name JANE:-

It is the English form of the Old French name Jehanne, which was an old feminine form of the male name Johannes or Ioannes (also the source of the English name JOHN),

[1931census]

female given name JANE:-

It is the English form of the Old French name Jehanne, which was an old feminine form of the male name Johannes or Ioannes (also the source of the English name JOHN),

I'm sorry? I apologise, but I thought I was clear about the fact that Jane was not her real name, and I am seeking clarity on her father, not her alias.

[AlanBoyd]

This table shows expected shared DNA for various relationships.

https://dragoninvestigation.com/2021/09/07/is-that-dna-match-a-1st-cousin-half-uncle-aunt-or-half-nephew-niece/

I’m hopeless at this sort of thing but I think your scenario means that Jane would be Jack Katz’s half aunt. The DNA match that you have is half of the lower limit for that relationship.


Apologies if you already know all of this and were looking for something else.

Expecting to be corrected…

EDIT
OK, spotted my own mistake, the DNA match is with Jane’s descendant, not Jane. More thinking…

[Rena]

female given name JANE:-

It is the English form of the Old French name Jehanne, which was an old feminine form of the male name Johannes or Ioannes (also the source of the English name JOHN),

I'm sorry? I apologise, but I thought I was clear about the fact that Jane was not her real name, and I am seeking clarity on her father, not her alias.

I have a couple of illigitimate children in my tree.  A couple were not allowed to marry until two years after the birth of their daughter who they named "Williamina" after father William.  This illustrates why I followed your lead and showed there is usually a feminine name to every male name.

The other child was given the full name of the father (full name = feminised given name plus surname plus mother's surname) who sailed away to war before parents could arrange to be married. 

[AlanBoyd]

This table shows expected shared DNA for various relationships.

https://dragoninvestigation.com/2021/09/07/is-that-dna-match-a-1st-cousin-half-uncle-aunt-or-half-nephew-niece/

I’m hopeless at this sort of thing but I think your scenario means that Jane would be Jack Katz’s half aunt. The DNA match that you have is half of the lower limit for that relationship.


Apologies if you already know all of this and were looking for something else.

Expecting to be corrected…

EDIT
OK, spotted my own mistake, the DNA match is with Jane’s descendant, not Jane. More thinking…

Looking again at the diagram I think that the relationship between your mother and Jack Katz is ‘half first cousin once removed’ with a DNA match predicted in the range 57-530 cM. So the match that you have is consistent with the relationship being what you propose.

[1931census]

female given name JANE:-

It is the English form of the Old French name Jehanne, which was an old feminine form of the male name Johannes or Ioannes (also the source of the English name JOHN),

I'm sorry? I apologise, but I thought I was clear about the fact that Jane was not her real name, and I am seeking clarity on her father, not her alias.

I have a couple of illigitimate children in my tree.  A couple were not allowed to marry until two years after the birth of their daughter who they named "Williamina" after father William.  This illustrates why I followed your lead and showed there is usually a feminine name to every male name.

The other child was given the full name of the father (full name = feminised given name plus surname plus mother's surname) who sailed away to war before parents could arrange to be married.

Oh, I understand. Jane's real name was pretty unique, and definitely not related to any of the Katz brothers. Furthermore, Brother 1 (the most likely candidate) most likely never had any intention of marrying Jane's mother, as he was married.