Download How To Work Pedigree Charts

How To Work Pedigree Charts
HOW TO WORK PEDIGREE CHARTS
Pedigree charts are graphic representations of inheritance in a family. There are certain features
common to all charts. Males are represented by squares and females by circles. If an individual
exhibits a trait, the circle or square is filled in. If they lack a trait, the circle or square remains open.
Marraiges (or matings) are indicated by lines connecting a circle to a square. Offspring are shown as
connected lines under the parents.
Test questions often ask whether the trait indicated on a pedigree chart is
1.
2.
3.
4.
5.
sex-linked dominant
sex-linked recessive
autosomal dominant
autosomal recessive
holandric.
Holandric genes are often easy to eliminate because any female on the chart exhibiting the trait
cannot be holandric (remember, only males are holandric).
Below is a pedigree chart tracing a trait in a family. Try to figure which of the five possiblilites listed
above fit the pedigree chart.
http://webhome.broward.edu/~fsearcy/pedigree.html (1 of 3) [1/4/2011 6:40:01 AM]
How To Work Pedigree Charts
The best way to work out the anwer is to simply choose one of five choices; i.e.
linked dominant. If the trait is sex-linked dominant, then for a female, XPXP or
p
female with the trait. The representation of X
exhibit the trait.
p
X
p
XPX
, sexwould indicate a
would indicate a normal female that does not
For example, XPY would indicate a male with the trait and X
exhibiting the trait.
p
Y would indicate a normal male, not
To find out if the trait is sex-linked dominant, simply trace the pedigree chart out by substituting
representations shown above for each figure. For example a female with a filled circle would have to
have at least one gene for the trait. An open circle would indicate a female homozygous recessive for
the trait.
http://webhome.broward.edu/~fsearcy/pedigree.html (2 of 3) [1/4/2011 6:40:01 AM]
How To Work Pedigree Charts
The pedigree chart indicates it is not a sex linked dominant trait. What is
inheritance?
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http://webhome.broward.edu/~fsearcy/pedigree.html (3 of 3) [1/4/2011 6:40:01 AM]
the pattern of