Genetics problems with family trees solved. (Page 27)
Another type of genetic problem is those of genealogical trees (or pedigrees). They are exactly the same as the ones you have done so far, in which some character is transmitted by genetic inheritance to the descendants. The only difference is that the transmission of this character is represented by a genealogical tree, in which males are represented by a square and females by a circle. Individuals who have this character are colored in black and those who do not have it, in white. If the individual is only a carrier, without manifesting that character, it may appear in gray or colored black as a half square or circle.
When you practice with any of these problems you will see that they are as easy and fun to solve as the previous ones.
Jcmorin en Wikipedia en inglés [Dominio público Dominio], via Wikimedia Commons
Before you start doing the problems, you have to keep a few things in mind:
- Individuals of the same generation are represented in the same row, usually numbered with Roman numerals.
- Males are represented by squares and females by circles. If they have a certain character, they appear colored.
- The biggest difficulty you may have is knowing if it is a sex-linked character or disease or not.
- If it is a case of inheritance linked to the Y chromosome, all male descendants of that male who has that character will have it. If there is any woman who is affected by this characteristic, we must rule out that it is linked to the Y chromosome, since they do not have a Y chromosome. Similarly, a son cannot have this characteristic linked to the Y chromosome if his father does not present it.
- If it is a case of recessive inheritance linked to the X chromosome:
- If a father does not present a character but his daughter does, we can rule out that it is a case of recessive inheritance linked to the X chromosome, since it is not possible for a father XA Y to have a daughter XaXa.
- If a mother presents a character but her son does not present it, we will rule out that it is a recessive character linked to sex, since a mother XaXa cannot have a child XAY.
- If a father has an X-linked dominant character (XAY), all of his daughters (XAX) must have it. If not all of your daughters have it, it will not be X-linked.
In addition to the problems on this page, you have more family tree problems at: