The expected amount of autosomal DNA shared between people who are related to each other can be worked out by assuming that each parent contributes half. (In reality there is some statistical range but leave that to one side…)

According to my understanding, a child whose parents are brother and sister could expect to share 62.5% of autosomal DNA with either of his or her parents. Do you agree with this analysis?

Can you contrive any circumstances in which two people would share 37.5% of DNA?

dv said:

The expected amount of autosomal DNA shared between people who are related to each other can be worked out by assuming that each parent contributes half. (In reality there is some statistical range but leave that to one side…)

According to my understanding, a child whose parents are brother and sister could expect to share 62.5% of autosomal DNA with either of his or her parents. Do you agree with this analysis?

Can you contrive any circumstances in which two people would share 37.5% of DNA?

One of them is a chimera ?

Cymek said:

One of them is a chimera ?

+1

dv said:

Can you contrive any circumstances in which two people would share 37.5% of DNA?

How about half siblings?

Witty Rejoinder said:

dv said:

Can you contrive any circumstances in which two people would share 37.5% of DNA?

How about half siblings?

That seems to be 25%

dv said:

Witty Rejoinder said:

dv said:

Can you contrive any circumstances in which two people would share 37.5% of DNA?

How about half siblings?

That seems to be 25%

the offspring of first cousins

Arts said:

dv said:

Witty Rejoinder said:

How about half siblings?

That seems to be 25%

the offspring of first cousins

The electric internet says “3/4 siblings or sibling-cousins” so I just need to work out what that means.

And WP says

Three-quarter
Three-quarter siblings have one common parent, while their unshared parents have a mean consanguinity of 50%. This means the unshared parents are either siblings or parent and child (similar terminology is used in horse breeding, where it occurs more frequently). Three-quarter siblings share more genes than half siblings, but fewer than full siblings.

“Sibling cousins” are those who have the same mother with their fathers being brothers or cousins or who share the same father with their mothers being sisters or cousins. This is a broader category than, but inclusive of, the 3/4 sibling above.

—-

Wow, it’s just a whole world of families out there

• Can you contrive any circumstances in which two people would share 37.5% of DNA?

Two people who share three out of four grandparents?

dv said:

And WP says

Three-quarter
Three-quarter siblings have one common parent, while their unshared parents have a mean consanguinity of 50%. This means the unshared parents are either siblings or parent and child (similar terminology is used in horse breeding, where it occurs more frequently). Three-quarter siblings share more genes than half siblings, but fewer than full siblings.

“Sibling cousins” are those who have the same mother with their fathers being brothers or cousins or who share the same father with their mothers being sisters or cousins. This is a broader category than, but inclusive of, the 3/4 sibling above.

—-

Wow, it’s just a whole world of families out there

Unless you’re a royal or a horse breeder it probably isn’t that important.

party_pants said:

dv said:

And WP says

Three-quarter
Three-quarter siblings have one common parent, while their unshared parents have a mean consanguinity of 50%. This means the unshared parents are either siblings or parent and child (similar terminology is used in horse breeding, where it occurs more frequently). Three-quarter siblings share more genes than half siblings, but fewer than full siblings.

“Sibling cousins” are those who have the same mother with their fathers being brothers or cousins or who share the same father with their mothers being sisters or cousins. This is a broader category than, but inclusive of, the 3/4 sibling above.

—-

Wow, it’s just a whole world of families out there

Unless you’re a royal or a horse breeder it probably isn’t that important.

dv said:

Can you contrive any circumstances in which two people would share 37.5% of DNA?

Two children who have one parent in common and whose other parents were siblings.

dv said:

The expected amount of autosomal DNA shared between people who are related to each other can be worked out by assuming that each parent contributes half. (In reality there is some statistical range but leave that to one side…)

According to my understanding, a child whose parents are brother and sister could expect to share 62.5% of autosomal DNA with either of his or her parents. Do you agree with this analysis?

Can you contrive any circumstances in which two people would share 37.5% of DNA?

Where did you get the 62.5%?

A person shares roughly 50% of autosomal DNA with each parent, and roughly 50% of autosomal DNA with each sibling. Aunt/uncle with nephew/niece would tend to be 25% and first cousin would be roughly half that.

If brother and sister have a child (presumably out of wedlock) then, um … I’ll get out the coloured crayons to work it out.
If father and daughter have a child, ditto.

Ah, wait, a key word that requires definition is “share”. Consider the case where person 1 has genetic code AB and person 2 has genetic code AA. Depending on the definition of “share”, we could have person 1 sharing 50% of DNA with person 2, but person 2 sharing 100% of DNA with person 1. It that a reasonable interpretation?

dv said:

And WP says

Three-quarter
Three-quarter siblings have one common parent, while their unshared parents have a mean consanguinity of 50%. This means the unshared parents are either siblings or parent and child (similar terminology is used in horse breeding, where it occurs more frequently). Three-quarter siblings share more genes than half siblings, but fewer than full siblings.

“Sibling cousins” are those who have the same mother with their fathers being brothers or cousins or who share the same father with their mothers being sisters or cousins. This is a broader category than, but inclusive of, the 3/4 sibling above.

—-

Wow, it’s just a whole world of families out there

Fascinating.