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Today I am going to introduce you to pedigree chart.
Pedigree chart is like a family tree but shows more than just the relationship between family
members. Pedigree chart shows relationships between
family members and the inheritance patterns of certain traits among the family members
through generations. It is used to identify the phenotypes of an organism.
What types of traits are represented using Pedigree Charts?
Pedigree charts are used to represent variety of genetic traits such as cleft chin, hair
line, freckles and more. Who Uses Pedigree Charts?
Pedigree charts are used by doctors and scientists to study genetic disorders that are passed
on from generation to generation such as cystic fibrosis, hemophilia, breast cancer and more.
Pedigree chart is constructed using special symbols and not any particular language. This
way everybody can understand. In a pedigree diagram, a male is represented
using squares and a female is represented using circles.
The square is shaded in if the male expresses the trait. The circle is shaded in if the
female expresses the trait. Horizontal line connecting the male and the
female represents the marriage. Vertical lines dropping down from this horizontal line show
the children of the couple. The oldest sibling is to the left and youngest to the right.
The top level represents the first generation and decreases as we go down the tree.
This slide shows a pedigree chart with three generations.
Let us look at a pedigree chart for a specific trait like attached and detached earlobes.
Free earlobes are those that hang below the point of attachment to the head. Attached
ear lobes are attached directly to the side of the head. Free earlobes are dominant to
attached earlobes. That means attached earlobe is a recessive allele.
Here is a pedigree chart of a family in which some members have attached earlobe. It shows
three generations of the family represented by roman numerals. Since the male in first
generation is shaded in, he has the recessive alleles for attached earlobes and hence expresses
this trait phenotypically. The female is not expressing attached earlobes.
This couple have 3 children 2(male), 3(female), and 4(female).
None of these children express attached earlobe phenotypically.
Two of the children, the oldest 2(male) and youngest 4(female) are married.
Their spouses also do not express attached earlobe.
Each of these couples has children as shown in the third generation. However, only the
child number 5 has expressed the attached earlobe phenotypically.