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Exceptions to Mendel’s Rules

Exceptions to Mendel’s Rules. Objective 3.04 Interpret and predict patterns of inheritance. Types of Dominance. There are three types of dominance. Complete dominance Incomplete dominance Codominance. Complete Dominance. This is the type of dominance that we have already learned.

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Exceptions to Mendel’s Rules

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  1. Exceptions to Mendel’s Rules Objective 3.04 Interpret and predict patterns of inheritance

  2. Types of Dominance There are three types of dominance. • Complete dominance • Incomplete dominance • Codominance

  3. Complete Dominance • This is the type of dominance that we have already learned. • The heterozygote will express the dominant trait.

  4. Example of Complete Dominance Let’s look at flower color. • Suppose red is dominant to white. • R= ____ and r = _____ • If a flower is Rr, it will be red.

  5. Complete Dominance X R R Rr rr Rr r RR Rr Rr r Genotypic ratio All Rr Phenotypic ratio All red Rr

  6. Complete Dominance Cross two heterozygous red flowers….. What is the genotypic ratio? What is the phenotypic ratio?

  7. Incomplete Dominance • Results in the blending of traits. • The heterozygote shows a blend of the dominant and recessive traits. • Happens due to a weak (less active) gene.

  8. Incomplete Dominance Example In snap dragons, the color for red and white flowers shows incomplete dominance. R = red r = white RR = red Rr = pinkrr = white

  9. Incomplete Dominance RR X rr Red white R R r Rr Rr r Rr Rr Rr Pink Genotypic Ratio All Rr Phenotypic Ratio All pink

  10. Incomplete Dominance Let’s cross two pink flowers Rr X Rr R r Rr RR R Rr r rr Genotypic Ratio 1 RR: 2Rr: 1rr Phenotypic Ratio 1 red: 2 pink:1 white (Note the 3 phenotypes)

  11. Incomplete Dominance

  12. Codominance • Co-dominant alleles result in the expression of BOTH traits!!! • Each trait receives it’s own capital letter !!!! (They are both equally dominant.) • Example letters: R and W • RR = red • WW = white • RW = red AND white

  13. Codominance Let’s cross a red flower with a white flower. Red flower genotype = _____ White flower genotype = ____ What is the genotypic ratio? What is the phenotypic ratio?

  14. Codominance X

  15. Codominance Cross two red and white flowers: What is the genotype of both flowers? ________ What is the genotypic ratio? What is the phenotypic ratio?

  16. Multiple Alleles • A multiple allele is when there are more than two alleles for one trait. • Human blood typing is an example. • The possible alleles are: • IA • IB • i

  17. Human Blood Types

  18. Blood Proteins • Antigen = Proteins • that identify the • blood cell. • Antibody = Proteins • that “attack” • foreign blood.

  19. Blood Type Practice Problems • Gertrude McFuzz has type AB blood. She marries Bubba Slicker. Bubba has type O blood. What are the possible genotypes of their children? Gertrude’s genotype = ______ Bubba’s genotype = ______ Possible genotypes:

  20. This is the Little family. Mr Little has type A blood and Mrs Little has type B blood. They have three children, Stuart, Timmy and Nancy. If Stuart has type O blood, what are the genotypes of Mr and Mrs Little? Suppose Mr Little is heterozygous but Mrs Little is not. What are the possible blood types of the Little children?

  21. Polygenic Traits • When traits are controlled by more than one gene. This can be a combination on multiple chromosomes. • Provides a wide range of phenotypes • Examples – Height, hair color, skin color, eye color.

  22. Polygenic Traits

  23. Human Eye Color • Controlled by 2 genes on 2 • different chromosomes. • Gene #1 • B = brown • b = blue • Gene #2 • G = green/hazel • g = blue BBGG = dark, brown eyes bbgg = blue eyes bbGG = blue/green or green eyes BBgg = darker green or hazel eyes

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