Pedigree Charts

A pedigree chart is a diagram that shows a family history and represent genetic relationships. It is almost the same thing as a family tree. The more complicated version is used in genetics as a way to determined how a certain genetic disease was distributed through the family. It can also be used to determine where inherited traits (such as attached/unattached earlobes, dimples, freckles, naturally curly/straight hair, hitchhiker’s thumb, color-blindness, Widow’s peak, hair and skin color) come from. Usually genetic counselors will use this chart to help couples/families that are worried about passing genetic conditions on to their children, or people that are concerned about inheriting adult onset genetic conditions.




In the chart, squares represent males and circles represent females. Horizontal lines connecting the two indicate mating. Vertical lines extending down from those represent their children. The oldest generation is shown at the top, all the way to the current youngest generation, which is at the bottom. Any shaded or colored shapes represent the individuals affected with the disease, or simply the people that have a certain inherited trait. Each row is a generation, which is represented by the roman numerals in each picture.




An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop. Recessive inheritance means both genes in a pair must be defective to cause disease. People with only one defective gene in the pair are considered carriers. But they can pass the abnormal gene to their children. If you are born to parents who both carry an autosomal recessive change (mutation), you have a 1 in 4 chance of getting the malfunctioning genes from both parents and developing the disease. You have a 50% chance of inheriting one abnormal gene. If a disease is autosomal dominant, it means you only need to get the abnormal gene from one parent in order for you to inherit the disease. Dominant inheritance means an abnormal gene from one parent is capable of causing disease, even though the matching gene from the other parent is normal. The abnormal gene "dominates" the pair of genes. If just one parent has a dominant gene defect, each child has a 50% chance of inheriting the disorder. Recessive inheritance occurs when both matching genes must be abnormal to produce disease. If only one gene in the pair is abnormal, the disease does not show up or is mild. Someone who has one abnormal gene (but no symptoms) is called a carrier. A carrier can pass this abnormal gene to their children.
Here is a video you can watch that explains it a bit more:
http://www.5min.com/Video/Pedigree-Chart-Problem-Review-151018111



Questions:
1. Explain the relationship in this pedigree chart(above), using words that describe generation, gender, parents, children, and who has the inherited traits.


2. In which ways can a pedigree chart help a married couple who is thinking of having children?


3. Is it possible that the pedigree above is for an autosomal recessive disorder? Why or why not?