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Pedigrees
Pedigree charts show a record of the family of an individual. It can be used to study the transmission of a hereditary condition. It is particularly useful when there are large families and a good family record over several generations.
You cannot make humans of different types breed together so pedigree charts provide one of the few ethical ways of studying human genetics. Today genetic engineering has new tools to offer doctors studying genetic diseases but a genetic counselor will still use pedigree charts to help determine the distribution of a disease in an affected family.
Pedigrees
The pedigree chart of Queen Victoria of England illustrates inheritance of hemophilia A. Queen Victoria herself was a carrier due to a chance mutation. Her children married other royalty and passed the trait throughout the royal families of Europe.
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Pedigrees
A pedigree is a diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships. These diagrams make it easier to visualize relationships within families, particularly large extended families. Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases. Some sample pedigrees are shown below.
Pedigrees
Pedigrees are very similar to family trees, except pedigrees study a specific trait within a family. A pedigree is often used to trace the transmission of hereditary diseases. Conventions for using Pedigrees Males are represented by a square.
Females are represented by circle. Shaded symbols represent a person that expresses the studied trait. 2
Pedigrees
Conventions for using Pedigrees Every generation (row) is represented by a Roman numeral, Each member in a generation is represented by an Arabic numeral.
(Arabic numerals numbered from the left.) For example, the affected individuals in the pedigree below are II3, IV2 and IV3.
Pedigrees
Conventions for using Pedigrees In the pedigree chart, individuals are placed in a generation (a row in the chart) from oldest to youngest (left to right).
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Pedigrees
Pedigrees
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1. Consider this pedigree for the dominant trait of tongue­rolling.
A. State the relationship of each of the following to individual II­3: I ­ 2 ______________
II­2 ______________
II ­ 5 ______________ III­2 ______________
III ­ 3 ______________
B. State the genotype of the following individuals:
I ­ 2 ______________ III­3 ______________
II­1 ______________ III­4 ______________
III ­ 2 ______________ 2. The pedigree chart below shows inheritance of the gene that causes albinism. A and B represent a couple who had five children, including C and E. Only one of the children, E, had albinism. “E” and her husband had five children, including G. In the pedigree below write the genotypes of the individuals who are labeled with letters, using A to represent the dominant allele and a to represent the recessive allele. HINT:Start by indicating the genotypes of E and F. a) Determine if this is a dominant or recessive trait and explain why. b) Label the genotypes of the individuals who's genotype that you know for certain.
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3. Analyze the pedigree below to determine if it could fit the mode of inheritance listed in the questions. a) The pedigree could be for a trait that has an autosomal recessive mode of inheritance. b) Explain why you answered true or false.
c) The pedigree could be for a trait that has an autosomal dominant mode of inheritance. d) Explain why you answered true or false.
e) The pedigree could be for a trait that has an X­linked recessive mode of inheritance. f) Explain why you answered true or false.
The pedigree below is an example of the inheritance of a particular type of dwarfism.
Individuals afflicted with dwarfism are shaded: individuals of normal height are not shaded.
The genotype of individual #6 is:
(A) AA (B) Aa (C) aa (D) impossible to determine due to insufficient data.
Explain the inheritance of this rare trait in the pedigree.
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Pedigrees
Here is a pedigree chart for three generations. The ABO phenotypes are listed for the known blood types. The mother in the first generation has the AB genes since her phenotype is AB. In the mating for the second generation, the genotype for the father could either be BB or BO since his father's phenotype is unknown. It would appear the mother is AA since both her parents are A, but..... Look at their children's blood types. What is the mother's genotype now since both children are B? Pedigrees
Sample Problem:
Making your own family pedigree is easy. All the materials you will need is paper, a pencil or pen and a coloured marker. Draw an outline of your family starting with your grandparents, leading to your parents, uncles, aunts and then yourself, any siblings or cousins. The ability to roll one's tongue is a noticeable dominant trait. Anyone who can roll their tongue has the dominant allele R while those who cannot have the genotype rr. Find out if you can roll your own tongue, if not enter your genotype on the pedigree as rr. If you can, write your genotype as one R for you have the dominant gene. Ask family members on your pedigree if they are able to roll their tongues. Then write down the appropriate genotypes by their symbol on the chart.
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