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Understanding a Pedigree Chart A family history of a genetic condition.

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1 Understanding a Pedigree Chart A family history of a genetic condition

2 Quick Review Genotype = what genes someone has Genes are usually represented by a letter, a capital letter for the dominant trait, a small case for the recessive. Example: Tongue Rolling is dominant, so we use R to represent the tongue rolling Inablility to roll your tongue is recessive so we use r to represent the non-rolling gene For every trait, you get a gene from each parent

3 Genotypes and Phenotypes Mom and Dad are Rr-that is their genotype, they can also be described as heterozygous- they have 1 of each gene What is their PHENOTYPE? The youngest son has a genotype of rr-he is Homozygous recessive-2 copies of the recessive gene His phenotype? I can’t Roll my Tongue!

4 Some common dominant and recessive traits Widow’s peak is dominant. You can be homozygous dominant (WW) or heterozygous (Ww) and you will have widow’s peak What is your genotype and phenotype if you’re homozygous recessive?

5 Making a Pedigree Chart Pedigree charts are made to chart family history and see how traits are passed A genetic counsellor will use pedigree charts to help determine the distribution of a disease in an affected family

6 Symbols Shade individuals that have the trait you’re studying Boys = squares (Lucy always calls Charlie Brown a ‘block head’) Girls = circles

7 Married-connected at side Siblings-connected at TOP not at the side (hopefully not siblings AND married) Oldest child-to the left Question-if shaded individuals in this pedigree have blue eyes, what is the GENOTYPE of the parents? Making a Pedigree Chart

8 Other Divorced, separated Deceased Identical twins Fraternal twins

9 Generations are identified by Roman numerals Organizing the pedigree chart I II III IV

10 Organizing the pedigree chart Individuals in each generation are identified by Arabic numerals numbered from the left Therefore the affected individuals are II3, IV2 and IV3 I II III IV 1 2 34567

11 What’s going on? Shaded = blue eyes 1 and 2 split after having 4, 2 then had kids with 3 and split with her too after 5-9 were born Genotypes of 1, 4,7? Genotypes of 2 & 3? Genotypes of 5,6, 8, 9, 10, 11, 12?


13 Make your own pedigree Using your own family, make your own pedigree chart Must at LEAST include grandparents, parents, & your generation Pick one easy dominant or recessive trait and shade individuals that have it. You can guess who has it if you don’t know for sure. (Don’t pick a trait that EVERYONE in your family has) Label yourself, grandparents, cousins, etc Put a key on the pedigree so I know what shaded means. Ex.- shaded people have widow’s peak OR…you may create a pedigree chart for a fictional family of your choice. For example, a family in a book you read or a movie you have seen (ex: Twilight series, Harry Potter, etc)

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