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Father’s Paternal Grandfather PEDIGREES & SEX-LINKED TRAITS & DISORDERS Father’s Father Father’s Paternal Grandmother Father Father’s Maternal Grandfather Father’s Mother Father’s Maternal Grandmother Me Mother’s Paternal Grandfather Mother’s Father Mother’s Paternal Grandmother Mother Mother’s Maternal Grandfather Mother’s Mother Mother’s Maternal Grandmother WHAT IS A PEDIGREE? • A pedigree is a chart, similar to a family tree, that follows traits throughout generations. SYMBOLS • Each symbol in a pedigree has a meaning. • Males are represented by squares • Females are represented by circles • If a person’s square or circle is empty, or not shaded in, then they do not carry the trait that is being analyzed in the pedigree. • However, if someone is affected by the trait being analyzed, then their square or circle is completely shaded in. CARRIERS • A carrier is someone that carries the trait being analyzed, but does not exhibit the trait in question. Essentially, a carrier is heterozygous. • A carrier’s square or circle is filled in half way to show that they carry, but do not exhibit, the trait in question. • OTHER SYMBOLS • A horizontal line joining shapes indicates marriages • A bracket from the marriage line indicates children SEX-LINKED TRAITS VS. AUTOSOMAL TRAITS • Autosomal traits have to do with body chromosomes • Sex-linked traits have to do with the sex chromosomes. • Sex-Linked traits or disorders, such as baldness (a trait), tend to occur more in one gender or another, while an autosomal trait or disorder tends to affect both genders evenly. EXAMPLE OF A SEX-LINKED TRAIT DISORDER • Baldness is a Sex-Linked trait that is carried on the X Chromosome. It shows up in males more often than females because females have a second X chromosome that can mask the recessive trait. Men only have the one X chromosome, so if they receive the bald gene from their mother, then they have no other X to mask the trait. Therefore, they will be bald. PEDIGREE USE • Pedigrees can be used to follow traits, such as baldness, and disorders, such as Huntington’s disease, throughout generations.
