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Pedigrees Human Heredity What we have covered so far… • • • • • • • Monohybrid crosses Simple dominance Incomplete dominance Co-dominance Multiple alleles Sex-linked recessive Honors- Dihybrid crosses But wait there’s more!! • Pedigrees • Chromosomes • Karyotypes Pedigrees • In humans, scientist’s study a family history using a pedigree. • Pedigree- a diagram that traces the inheritance of a particular trait through several generations. By using boxes, circles and connecting lines, it is possible to diagram a family history of a genetic disease. How to read a Pedigree •Circles=females •Squares=males •solid objects= diseased individuals •half-solid objects= carriers •unfilled objects= genetically healthy individuals • A pedigree also uses a numbering system in which Roman numerals represent generations and the individuals are numbered using 1,2,3,4…. Autosomal Inheritance • affects both men and women Autosomal Dominant: - trait usually present in each generation Sex-Linked Inheritance • trait is carried on the X chromosome • affects mostly men • usually recessive Examples: hemophilia, color blindness, baldness Autosomal Recessive: - trait usually skips generations - will only show up if homozygous 1. 2. 3. 4. How many generations are listed above? 4 Is the trait above autosomal or X-linked? Autosomal Is the trait above dominant or recessive? Recessive How did #8 inherit the trait if his parents don’t express it? His parents must be carriers of the trait (heterozygous) 5. Why do sex-linked traits show up mainly in men? Men have only one X chromosome, and can’t be carriers If individual III-2 marries a person with the same genotype as individual I-1, what is the chance that one of their children will be afflicted with hemophilia?