1. 11.2 Complex Inheritance 2. A. Incomplete Dominance Heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes EX. Red x white = pink 3. B. Codominance Both alleles are expressed in the heterozygous condition Example: Sickle-Cell Anemia People who are homozygous have abnormal red blood cells that are shaped like a half moon Hemoglobin differs by one amino acid Results in slow blood flow and blocked vessels 4. Those heterozygous for this trait produce both kinds of blood cells (normal and sickle)these individuals can lead relatively normal lives. most common in black Americans whose families originated in Africa and white Americans whose families originated in countries surrounding the Mediterranean Sea 1 in 12 African Americans is heterozygous for this trait 5. C. Multiple Alleles Example 1: Blood Type a. The gene I has three alleles: IA, IB, & i b. These alleles determine your blood type: A, B, AB, and O 6. Blood Types 7. Importance of Blood Typing Your immune system recognizes the red blood cells that you have. If cells with a different protein enter your body, your immune system will attack them! 8. Blood Types Genotype Surface Protein Phenotypes IA IA or IA i A A IB IB or IB i B B IA IB A and B AB ii none O 9. Example 2: Coat Color of Rabbits Multiple alleles can demonstrate a hierarchy of dominance In rabbits, four alleles code for coat color: C, cch , ch , and c. 10. Coat Color of Rabbits Light gray Dark gray Chinchilla Albino Himalayan 11. D. Epistasis Variety is the result of one allele hiding the effect of another allele Example: Coat color in labrador retrievers varies from yellow to black No dark pigment present in fur Dark pigment present in fur eebb eeB_ E_bb E_B_ 12. E. Sex Determination Sex chromosomes determine an individuals gender 13. e. Sex Linked Traits Examples: 1.Color Blindness Carried on the X chromosome 14. 2. Hemophilia; Inability of blood to clot Carried on X chromosome 15. f. Polygenic Inheritance 1. Example: skin color 2. Variation in skin color indicates that between 3 and 4 genes are involved 16. 11.3 Chromosomes and Human Heredity 17. A. Changes in Chromosome Number What would happen if an entire chromosome was missing or if you had an extra chromosome? These mistakes often happen during meiosis. Nondisjunction=chromosomes fail to separate properly during cell division 18. 1. Unusual Numbers of Autosomes Most people have 23 pairs of chromosomes; 22 autosome pairs & 1 pair of sex chromosomes Some people have an extra chromosome (47 instead of 46) 19. Down Syndrome Caused by an extra 21st chromosome Karyotypes are used to locate extra chromosomes. 20. Unusual Number of Sex Chromosomes 1. Many problems may exist: X missing XO=Turners Syndrome, OY=death Extra X: XXX=nearly normal female, XXY=Male with Klinefelters Syndrome Extra Y: XYY=normal or nearly normal male 2. Any individual with at least one Y is male, and any individual without a Y is a female.