autosmal dna

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This project evaluates your understanding of the unique inheritance of autosomal DNA, the limitations of atDNA testing, and how atDNA is transmitted from one generation to the next.

The following is a comparison of the DNA of a paternal grandfather and a grandson on chromosome 1, where gray indicates the chromosome and brown indicates the shared segments of DNA:

Image of 1 line representing Chromosome 1. Within the line segment, it is grey, brown, grey, brown, grey.

On the basis of your understanding of autosomal DNA and this comparison, answer the following questions:

  1. Since this comparison is of a paternal grandfather and a grandson, it represents a single recombination. At least how many recombination events had to occur in order to observe this pattern?
  2. Based on the above comparison alone, can you determine the segments of DNA on chromosome 1 that the grandson received from his maternal grandmother? Why or why not?
  3. Let’s follow the same chromosome through to the next generation, to the grandson’s son, and compare it to the same paternal grandfather (now a great-grandfather). Could the comparison of the great-grandfather and great-grandson look like the result below? Why or why not?

Image of 1 line representing Chromosome 1. Within the line segment, it is grey, brown, grey, brown, grey, brown.

Hallie’s family tree is below. Amazingly, Hallie has tested all of her grandparents and five of her eight great-grandparents. Three of her great-grandparents, unfortunately, are deceased. Based on the results of the testing, Hallie has determined exactly how much DNA she obtained from the grandparents and great-grandparents that were tested, as shown in the table below.

Image of Hallie’s family tree.

Ancestor Shared Percentage
Grandparents John 24.0%
Jane 26.0%
Chris 20.0%
Cindy 30.0%
Great-grandparents Hugh 14.0%
Helen 10.0%
Philip DECEASED
Phyllis 15%
Thomas DECEASED
Theresa 10.0%
Morris DECEASED
Mary 17.0%
  1. Based on the family tree and the graph, what are the correct percentages for Philip, Thomas, and Morris? Adding all the great-grandparents’ percentages together, what is the total? At the great-grandparent level, do any of the percentages seem high or low compared to expected amounts. If so, which one(s)? Why or why not?

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