TBR Bio Section 9 Passage 15 Question 100

[ChodeNode]

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Anybody with this book able to explain this to me? The question asks which parent(s) gave an extra chromosome. To me it appears both mother and father contribute two gene, but the answer says one came from the father and two from the mother.

I'll try to ASCII out the blot using pluses for blot bars and periods for white space:

Mother Kid Father
----------------------------------------------------------------
1................|...........................|.....+
2............+..|.....................+....|
3......+....+..|....+...............+....|.....+
4................|.............+............|............+
-----------------------------------------------------------------

To me, it looks like the mother gives via likes 2 and 3. The father gives via lines 3 and 4. How am I misreading this?

 

[ashtonjam]

Each vertical 'column' on the blot represents one chromosome. The mother has two chromosomes, one with only microsatellite allele 3 and the other with both 2 and 3. The father has a chromosome with 1 and 3 and another with only 4.

Looking at the kid with three chromosomes, you can tell that the one in the middle (allele 4) had to come from the dad because the dad is the only one with 4. The kid's other two chromosomes come from the mother because the dad's pattern (1 and 3) is not found in the kid's chromosomes. Both of the mom's patterns (3) and (2 and 3) are found in the kid's karyotype as (3) and (2 and 3) on either side of the (4).

Didn't look at the book but it seems right.

 

[ChodeNode]

That makes total sense, thanks. My problem was I wasn't viewing the column as the chromosome, I was looking at the row as the chromosome. I had done another problem where it happened to work out that viewing it as a row worked, but it seems like I just got lucky.

Lesson learned. Thanks.