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Incomplete D ominance

Incomplete D ominance. Incomplete Dominance Codominance. Prior to Mendel. Many scientists believed that hybrids would have a blending of traits Although Mendel never found any examples of new traits or blended traits produced by the combination of different alleles, many do exist in nature.

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Incomplete D ominance

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  1. Incomplete Dominance Incomplete Dominance Codominance

  2. Prior to Mendel • Many scientists believed that hybrids would have a blending of traits • Although Mendel never found any examples of new traits or blended traits produced by the combination of different alleles, many do exist in nature

  3. A) Incomplete Dominance • When two alleles are equally dominant, they interact to produce a new phenotype • Neither allele is dominant over the other, so the heterozygous genotype has its own phenotype

  4. Snapdragon Example

  5. A red snapdragon is crossed with a white snapdragon • What are their genotypes? • (CR CR) x (CW CW)

  6. What will be the genotype and phenotype of the F1 generation • CR CW = Pink • What will be the genotype and phenotype of the F2 generation

  7. Additional Question • In guinea pigs, colour of coat is determined by at least three alleles. Yellow coat is determined by the homozygous genotype YY, white by the homozygous genotype WW, and cream by the heterozygous genotype YW. • Determine the expected genotype and phenotype ratio of the F1 generation which would result from a cross between: a) two cream coloured guinea pigs; • b) a yellow coated and a cream coated animal

  8. Answer • Let YY represent yellow. • Let WW represent white. • Let YW represent cream. • a) P generation phenotypes: cream x cream • genotypes: YW x YW • gametes: Y W Y W • Punnett square: • Y W • Y YY YW • W YW WW • The expected phenotypic ratio of the F1 generation is • 1 yellow: 2 cream : 1 white. The genotypic ratio is • 1 YY: 2 YW: 1 WW • b) P generation phenotypes: cream x yellow • genotypes: YW YY • gametes: Y W Y Y • Punnett square: • Y W • Y YY YW • Y YY YW • The expected phenotypic ratio of the F1 generation is • 1 yellow: 1 cream. The genotypic ratio is 1 YY: 1 YW.

  9. Additional Question • Howdy! My name is Bob Howard, and I own 20 purebred red cows. Something strange happened several months ago. During a violent storm, all of the fences that separate my cattle from my neighbors cattle blew down. During the time that the fences were down, three bulls, one from each neighbor, had access to my cows. For awhile, I thought that none of the bulls found my cows, but over the months, I have come to the conclusion that all of my cows are expecting calves. One of the bulls is the father. Which bull is it? • A local college professor told me to use a little genetics detective work to figure out who the father is. He told me to collect information about each of the bulls, and to read articles about genetics and Gregor Mendel's experiments in genetics. So, I did exactly what he said. I compiled the information. Now, I need your help to make sense of the data and to figure out who the father is. • After reading through the information, maybe you can tell me why my red cows had 9 roan calves and 11 red calves. I don’t really understand how this happened. When you have determined which bull is the father, please tell me the answer.

  10. The 3 Possible Culprits This is Rocky. He is a 2,200 pound Red bull. The colour of Rocky&’s calves, if mated with a red cow, can be determined by using a Punnett square. His offspring will also be unique in colour compared to the other two bulls. This is Rufus. He is a 1,920 pound White bull. The colour of Rufus’ calves can also be figured out, if he is mated with a red cow, by using a Punnett square. The colour of his calves will also differ from the other two bulls offspring. This is Ferdinand. He is 2,000 pound Roan bull. The laws of genetics tell us that the offspring he produces will probably be different, in colour, than the other two bulls’ offspring. Using a Punnett square, you can see the gene combinations, for colour, that Ferdinand’s offspring could have if he mates with a red cow. The colour of Ferdinand’s calves has to do with probability.

  11. Who did it?

  12. B) Codominance

  13. Another type of incomplete dominance • Both alleles are expressed at the same time • There are more than one dominant allele

  14. Shorthorn Example • A red bull crossed with a white cow produces a roan calf CwCw CRCR

  15. The roan calf has intermingled white and red hair

  16. Note • Codominance is not an example of “blending inheritance” since the original phenotypes reappear in the second generation • The genotypes are not blended and they still obey Mendel’s law of segregation • It is only the phenotype that appears to blend in the heterozygotes

  17. The gene for haemoglobin Hb has two codominant alleles: HbA (the normal gene) and HbS (the mutated gene). There are three phenotypes:

  18. Cat Coat Example • Black x Orange = Tortoiseshell

  19. Resource Link: http://gslc.genetics.utah.edu/units/basics/blood/types.cfm

  20. Multiple Alleles • So far, the inheritance examples we have looked at only have 2 alleles • Example: Brown hair or blonde hair, brown eyes or blue eyes, etc. • Most traits in nature are controlled by more than 2 alleles, such as human blood groups

  21. Multiple Alleles Recall:

  22. Multiple Alleles Recall:

  23. Multiple Alleles Recall:

  24. Multiple Alleles

  25. Multiple Alleles • When more than 3 phenotypes are possible, then more than 2 alleles for that trait must exist in the population. • However, individuals have only two of those alleles. Why? • Because only one allele is inherited from each parent

  26. Example of Multiple Alleles • The ABO system of human blood type involves three alleles (IA, IB, and i). • IA and IB – co-dominant, where “i” is recessive • As a result, there are four possible phenotypes or blood types: A, B, AB, and O.

  27. What do the Alleles Code For? • The blood types differ due to the molecules that are present on the outside of the red blood cells (antigens) • Antigens act as recognition factors for our immune system

  28. Type A Type AB Type B Type O What do the Alleles Code For? Both A & B No antigens

  29. What do the Alleles Code For? • When white blood cells do not recognize the antigen, it considers the cell an invader and produces antibodies to attack that cell • This is why receiving an incorrect blood type will cause agglutination (clumping).

  30. Human Blood Groups: Multiple Alleles AND Codominance • Human blood types are controlled by a single gene (expressed as an antigen: protein on surface of red blood cell)

  31. Example #1 • Suppose you have a father who is type AB and he has a child with a mother who is also type AB. What possible blood types may the child have?

  32. Example #2 • Is it possible for parents who are Type A and Type AB to have child that is type B?

  33. Judging from the results of this cross, the child could be type B. There is a 25% chance that the child could be type B. If you were to complete the cross using homozygous Type A, then you find a different result

  34. Summary Table

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  36. Summary Table

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  38. Summary Table

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