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Complex Patterns of Inheritance

Complex Patterns of Inheritance. Mendel’s Laws. Law of Segregation: Organisms inherit two copies of each gene, one from each parent Organisms donate only one copy of each gene in their gametes. Thus, the two copies of each gene segregate, or separate, during gamete formation.

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Complex Patterns of Inheritance

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  1. Complex Patterns of Inheritance

  2. Mendel’s Laws Law of Segregation: • Organisms inherit two copies of each gene, one from each parent • Organisms donate only one copy of each gene in their gametes. Thus, the two copies of each gene segregate, or separate, during gamete formation.

  3. Law of Independent Assortment: the alleles of different genes separate independently of one another during gamete formation

  4. I. Sex-linked traits • A sex-linked trait is a trait whose allele is located on either the X or Y chromosome.

  5. A) Hairy Ears: Gene on the Y Chromosome

  6. B) Most sex-linked traits on X chromosome are recessive • Examples include: hemophilia, red-green colorblindness, and a form of muscular dystrophy

  7. A person with red-green color blindness sees a number 2

  8. Hemophilia • In this pedigree, only males are affected, and sons do not share the phenotypes of their fathers. • Thus, hemophilia is linked to a sex chromosome–the X. • Expression of hemophilia often skips generations. • Thus, it is recessive. Extensive bruising of the left forearm and hand in a patient with hemophilia.

  9. Genotypes for females XHXH = normal blood clotting, non-carrier XHXh = normal blood clotting, carrier of gene XhXh = female with hemophilia Queen Victoria of the United Kingdom was a carrier of hemophilia

  10. Genotypes for Males • XHY = normal blood clotting • XhY = male with hemophilia • Tsarevich Alexei of Russia had hemophilia

  11. Cross a carrier mother with a normal father.

  12. No daughters with hemophilia, ½ of sons with hemophilia

  13. Cross a hemophiliac father with a normal (non-carrier) mother.

  14. All daughers are carriers, no sons have hemophilia.

  15. II. Incomplete Dominance • An individual displays a trait that is intermediate between the two parents • Example: a red snapdragon crossed with a white snapdragon produces pink offspring

  16. Red = RR, White = WW, Pink = RW

  17. Make a Punnett square for a red plant crossed with a white plant

  18. All offspring are pink, with RW genotype R R W W

  19. What happens if you cross two pink snapdragons?

  20. Offspring are 1 red, 2 pink, and 1 white R W R W

  21. 1 red (RR), 2 pink (RW), 1 white (WW)

  22. Incomplete dominance in horse coat color

  23. III. Codominance • Two dominant alleles are expressed at the same time • Roan coat color in horses or cows is an example • A roan horse has both red and white hairs

  24. Roan  has red and white hairs

  25. Parents  Codominance in chicken feather color. Black and White feathers 

  26. IV. Multiple Alleles • Genes with three or more alleles for a particular trait. • Examples are the ABO blood types, fur color in many animals.

  27. Coat color in rabbits

  28. List all possible genotypes for a: a) dark gray-coated rabbit CC, Ccch, Cch, Cc b)chinchilla rabbit cchcch, cchch, cchc c) Himalayan rabbit chch, chc d) white rabbit cc

  29. Predict the phenotype for a rabbit with a chcch genotype chinchilla Predict the phenotype for a rabbit with a Cch genotype dark gray • Would it be possible to obtain white rabbits if one parent is white and the other is chinchilla? Yes, if the chinchilla parent has a white allele

  30. Would it be possible to obtain chinchilla rabbits if one parent is Himalayan and the other is white? No, because chinchilla is dominant to both Himalayan and white, so the allele couldn’t be “hiding”. • A chinchilla rabbit is mated with a Himalayan. Some offspring are white. What are the parents’ genotypes? Himalayan is chc and chinchilla parent is cchc

  31. V. Polygenic traits • Traits that are influenced by 2 or more genes • Examples include human height, weight, hair color, eye color, and skin color

  32. Coat color in Labrador retrievers

  33. Coat color in Labrador retrievers

  34. VI. Epistasis • One gene that interferes with the expression of other genes. • Example is with albinism. • One gene interferes with all other genes for pigment production.

  35. VII. Traits influenced by the environment. • Color of hydrangea flowers (blue in acidic soil, pink in basic soil)

  36. Color of arctic fox • Human height, skin color, behavior

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