Males will always be squares and females will always be circles. If the square is shaded in, then it represents an affected male. If a circle is shaded in, then it represents an affected female. Clear circles and clear squares will be normal, or not affected.
-First thing you need to do, is determine if the pedigree chart shows an autosomal or sex-linked trait - If most of the males in the chart are affected (shaded in), then the disorder is sex-linked. If it is sex-linked the genotypes will be XX and XY with an exponent on the X. - If it is about a 50/50 ratio between males and females, then the disorder is autosomal. If it's autosomal the genotypes will be AA, Aa, or aa.
-Next determine if the disorder is dominant or recessive. -If the disorder is dominant, one of the parents must have the trait. -If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous. We identify generations using Roman numerals (I, II, III) and individuals using Arabic numerals (1, 2, 3). Always start counting from left to right.
After figuring out those two parts, you can now figure out the genotypes of all the individuals. You must keep in mind that an individual gets one allele from their mom and one allele from their dad.
If the trait is dominant and the circle is clear, you know the genotype is recessive, aa. If you know the individual is dominant you know one letter has to be dominant (A). You then use the children or parents to solve the second letter, which could be another dominant or a recessive allele. If one of the parents is recessive, that means their genotype is aa. Which means the only allele they can pass on is a. If you are looking at the children you will use the same reasoning. If 2 dominant parents have a recessive child that means the parents must be heterozygous (Aa). The only way to have a recessive trait is to have 2 recessive alleles.
Find the genotype of II 3.
First go to generation II, the second down. Then count the shapes until you get to individual 3. You should have gotten a circle that is shaded in. You need to first figure out if the pedigree is autosomal or sex-linked. The genotypes of those will look different. This pedigree shows autosomal, because there are not more males affected than females.
Then I need to figure out if this is showing a dominant or recessive trait. This is a recessive trait because the parents don't have it, it skips a generation.
Looking back at II 3, we see that its shaded in, so she has the trait, and the trait is autosomal, means the genotype will be aa.
P.I. Pedigree Investigator. You are going to look for genes that influence nicotine addiction.
Now that you have had some success with pedigrees, let's see if you can create one after listening to the following song.
I'm My Own Grandpa- 1947
Many, many years ago when I was twenty-three I was married to a widow who was pretty as could be. This widow had a grown-up daughter who had hair of red. My father fell in love with her and soon the two were wed. This made my dad my son-in-law and changed my very life For my daughter was my mother, 'cause she was my father's wife. To complicate the matter even though it brought me joy I soon became the father of a bouncing baby boy. My little baby then became a brother-in-law to dad And so he became my uncle though it made me very sad For if he is my uncle then that also makes him brother, To the widow's lovely daughter who, of course, was my step-mother. Father's wife then had a child which kept them on the run, And he became my grandchild, 'cause he was my daughter's son; My wife she is my mother's mother and it makes me blue, Because although she is my wife, she's my grandmother too. Now if she is my grandmother than I'm her grandchild And every time I think of it, it nearly drives me wild; For now I have become the strangest case you ever saw As husband of my grandmother I am my own grandpa. Chorus: Oh, I'm my own grandpa, I'm my own grandpa It sounds funny, I know, but it really is so Oh, I'm my own grandpa
Practice Problems
1. What does a clear square show?
2. Does the following pedigree show an autosomal or sex-linked trait?
3. Does the above pedigree show a recessive or dominant trait?
4. Does the following pedigree show an autosomal or sex-linked trait?
5. Does the above pedigree show a recessive or dominant trait?
6. Does the following pedigree show an autosomal or sex-linked trait?
7. Does the above pedigree show a recessive or dominant trait?