Complex inheritance
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This document discusses different forms of complex inheritance that cannot be explained by Mendel's principles of inheritance. It compares incomplete dominance, co-dominance, multiple alleles, and polygenic inheritance. Incomplete dominance results in a blended phenotype between two parent phenotypes. Co-dominance shows both parental phenotypes expressed together. Multiple alleles occur when there are more than two possible forms of a gene. Polygenic traits are influenced by multiple interacting genes.
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Complex inheritance
- 1. Objectives Discuss why Mendel’s principles cannot be applied to all situations. Compare and contrast different types of complex inheritance.
- 2. It’s complicated Mendel got lucky All of the traits that he studied were only controlled by two alleles Remember: an allele is a form of one gene (yellow or green) All of the traits were perfectly dominant or recessive
- 3. It’s complicated Unfortunately, most traits are not so neat and tidy
- 4. It’s complicated There are 4 forms of complex inheritance you need to know Incomplete dominance Co-dominance Multiple Alleles Polygenic inheritance
- 5. Incomplete Dominance Remember, a gene is the instruction for a protein Because there are two alleles for a trait, two proteins are being produced In Mendel’s studies, one protein dominated the other The dominant protein was shown
- 6. Incomplete Dominance Incomplete Dominance: One gene does not clearly dominate the other The phenotype of the offspring is a blend of the two parent phenotypes
- 7. Incomplete Dominance Example: A white flower is mixed with a red flower In incomplete dominance a white flower mixed with a red flower produces PINK offspring The offspring are a blend of the two parents Neither parent is seen in the offspring
- 8. Co-dominance Co-dominance: Neither phenotype dominates and BOTH are shown
- 9. Co-dominance Example: A red flower is mixed with a white flower In co-dominance a red parent flower and a white parent flower produce offspring with BOTH red AND white petals
- 10. Compare Incomplete dominance: Red + White = Pink Co-dominance: Red + White = Both red and white on the same flower
- 11. Multiple Alleles With all of the variety in the world it would make sense that some traits have more than two forms
- 12. Multiple Alleles Multiple Alleles: A trait for which there are more than 2 forms of a gene
- 13. Multiple Alleles Example: Blood Type There are three alleles for blood type IA IB i
- 14. Multiple Alleles Genotypes for type A blood are IA IA or IAi Genotypes for type B blood are IB IB or IBi Genotype for AB blood is IA IB Genotype for type O blood is ii
- 15. Polygenic Inheritance If you have noticed, most kids are a blend of their parents traits To this point all of the traits we have talked about have been controlled by different forms of ONE gene
- 16. Polygenic Inheritance Polygenic Inheritence Remember your words Poly = many What do you think POLYgenic inheritance means?
- 17. Polygenic Inheritance Polygenic inheritance: A trait that is controlled by multiple genes working together Some good examples Skin color Eye color Height
- 18. Polygenic Inheritance There are many genes that control skin color, eye color, or height The interaction of those genes controls the precise color of your skin, color of your eyes, or your height