Methods of Inheritance

Other Methods of Inheritance: Codominance and Incomplete DominanceThe Different Forms of InheritanceMendels Inheritance (Monohybrid + Dihybrid) = Last lessonIncomplete dominance = This lessonCodominance= This lessonSex linked = Next Lesson

Incomplete DominanceIncomplete dominance is another example of how some traits are inherited different from Mendel predicted.In incomplete dominance neither of the two alleles for the same gene can dominate the other.The result is that the phenotype is a blend of both parentsThis is similar to the old theory of blended inheritance.

Incomplete dominanceIncomplete Dominance: a condition in which neither of the two alleles for the same gene can completely conceal the presence of the other. As a result, the offspring or heterozygote exhibits a phenotype that is a mixture or somewhere between the a dominant and recessive phenotype.Example: Flower colour of SnapdragonsRed Flower x White Flower Pink Flower

4Practice Incomplete DominanceWhat would be the result if we crossed two pink snapdragon flowers (CRCW) together. What percentage of the offsrping would be pink? Red? White?

Codominance Inheritancea condition in which both alleles for a trait are equally expressed in a heterozygote: both alleles are dominantFor example: Roan animalRed Bull x White Cow Roan Calf (has red and white hair)

E.g. a Roan animalE.g. 2 Codominance

E.g. 3 CodominanceRulesChoose ONE letter to represent the trait and always use CAPITALS. (for example: colour of snapdragons, use capital C

The two alleles are represented as superscripts (example: R for Red (CR ) and W for White (CW )

Complete the hybrids using the same rules as monohybrids and dihybrids. Heterozygotes (CRCW) will display the intermediate trait (pink flowers)ExampleThe four oclock flower shows incomplete dominance. A pure red flower is crossed with a pure white flower. Use a punnett square to find the phenotypes and genotypes of the F1 generation and F2 generation

Multiple Allele GenesMost genes in the human body are actually controlled by more than 2 alleles = multiple allele genesOne common example is human blood typeIt is controlled by 3 alleles: iA and iB and i

Example:

12HomeworkEntire class: Examine sample problem on page 246H.W. # 1-4, 8, 9 (page 247)