Assignment - Relatedness Calculations

Charles II of Spain, with the distinctive Habsburg Jaw.


Learning Intentions

  • To understand what fraction of DNA is passed down from one generation to the next
  • To understand the effects of in-breeding


Notes

When we talk about mother and father in this unit, we are not using the term the same way it is used in broader society. In society, there are mothers and fathers who have no biological relationship to their children. There are chosen families that ignore the arbitrary boundaries created by biologists. These families are no less "real" than families that meet the scientific definition.

In addition, when we talk about male and female, we are not talking about men and women. There are men who are male and there are men who are female. There are women who are male and there are women who are female. There are also people who are intersex, "born with sex characteristics (including genitals, gonads and chromosome patterns) that do not fit typical binary notions of male or female bodies."

In biology, females are defined to be the sex that provides the larger gamete, the egg, containing 23 chromosomes. Males are defined to be the sex that provides the smaller gamete, the sperm, containing 23 chromosomes. In human biology, XX people are defined as male and XY people are defined as female. In avian biology, ZZ birds are defined as male and ZW birds are defined as female.

Every human child receives one half of their autosomal (chromosomes 1 to 22, not including the X/Y sex chromosomes) chromosomes from each parent. Since each parent receives half of the chromosomes from each of their parents, the child receives one quarter of their chromosomes from each grandparent.

Family tree in Cantonese.

In the English language, there are no special words to denote older or younger siblings. The husbands and wives of siblings are known as "brothers-in-law" and "sisters-in-law".

Notice how the Chinese words for mom and dad are very similar to the English words "mama" and "papa". Do you know the words for mom and dad in any other languages? Why do you think they sound so similar?

This is the family tree of the baa baa (father).

Father's family tree.

This is the family tree of the maa maa (mother).

Mother's family tree.


Questions

  1. Assuming that no one is married to a relative, figure out how much (on average) of each relative's autosomal DNA you have.
    1. Siblings family tree
    2. Baa baa's family tree
    3. Maa maa's family tree
  2. Imagine that someone has an aunt or uncle who expresses a trait that prevents them from having children. How is it possible for this trait to persist in the family, if the expression of this trait prevents the production of offspring?
  3. What percent of your DNA comes from:
    1. Each parent (first generation)?
    2. Each grandparent (second generation)?
    3. Each great-grandparent (third generation)?
    4. Each great-great-grandparent (fourth generation)?
    5. The nth generation?
  4. Examine the family tree of Charles II of Spain, shown on the left in the picture at the top of this page.
    1. How many paths are there from Charles II to Joanna of Castile?
    2. How many generations are there in the shortest path from Charles II to Joanna of Castile
    3. How many generations are there in the longest path from Charles II to Joanna of Castile?
    4. Extension:
      Examine the famiy tree of Charles II of Spain. Calculate the percentage of Charles' autosomal DNA that comes from each of the relatives.
      Assume that Isabella of Portugal, Anne of Bhoemia and Hungary, Christian II of Denmark, Albert V, and Francis I are completely unrelated to the Hapsburg family.

      The Spanish Hapsburg Family Tree



  5. About 8000 years ago, 17 women reproduced for every 1 man. What does this suggest about inbreeding during this period?