Beyond Dominant and Recessive Alleles

1. Beyond Dominant and Recessive Alleles Pages 272-274

2. Summary of Mendel’s Principles • Inheritance of biological characteristics is determined by units known as genes. • Some forms of a gene may be dominant and others may be recessive. • Each adult has two copies of each gene—one from each parent. These genes are segregated from each other when gametes are formed. • Alleles for different genes usually segregate independently from one another.

3. Incomplete Dominance • Neither allele is dominant • In some cases, an intermediate phenotype is shown • In snapdragons, flower color can be red, pink, or white. The heterozygous condition results in pink flowers • A white snapdragon crossed with a red snapdragon produces all pink offspring

4. Codominance • Both alleles can be expressed • For example, red cows crossed with white will generate roan cows. Roan refers to cows that have red coats with white blotches. • Black and white (erminette) chickens

5. Polygenic Traits • Traits that are produced by the interaction of several genes • Often times show a wide range of phenotypes. • Human skin color—more than 4 genes control this trait. • Intermediate is usually the norm—bell shape graph.

6. Multiple Alleles • A population might have more than two alleles for a given gene • Coat color in rabbits • Human genes for blood type • ABO blood grouping • A and B blood types are dominant O is recessive • Blood type lab

7. Picture Credits • http://fig.cox.miami.edu/~cmallery/150/mendel/c14x9incomplete-dominance.jpg • http://users.adelphia.net/~lubehawk/BioHELP!/wwxrw.jpg • http://www.biologycorner.com/resources/roancow.jpg • http://www.okc.cc.ok.us/biologylabs/Images/Tutorial_Genetics_Images/rbc-2.jpg • http://www.gwu.edu/~darwin/BiSc150/One/rose.GIF • http://www.smokehamfarm.com/Other%20Animals/OA-iro/DominiqueChicken(OVAL).gif