2. VARIATIONS OF INHERITANCE

3. Dominant Controlled Inheritance (aka “simple”) (quick review) So far, we have been looking at traits that are controlled by the dominant allele. A homozygous dominant or heterozygous genotype will result in the dominant trait being expressed. F = purple flower, f = white flower FF and Ff both result in a purple flower.

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6. Incomplete(Intermediate) Inheritance Scientists observed that some traits simply did not show this “dominance only” form of inheritance. Some phenotypes appear to be a mixture of the two parent phenotypes. incomplete When neither allele for a trait is dominant, it is called incomplete inheritance.

7. Incomplete Inheritance Let’s look at an example using FUR COLOR(or “F”). F B = allele for black dog fur F W = allele for white dog fur What happens if we cross one homozygous black dog and one homozygous white dog ? F B F B x F W F W

8. Incomplete Inheritance FBFB FBFB FWFW FWFW FBFWFBFW FBFWFBFW FBFWFBFW FBFWFBFW All the offspring have a heterozygous genotype.

9. Incomplete Inheritance Assume this trait is controlled by incomplete inheritance. The phenotype for the offspring would be be brown (or tan) colored fur. Since neither allele is dominant, they both get blended together.

10. Incomplete Inheritance Now, what would be the outcome if we crossed two of these brown-colored dogs?

11. Incomplete Inheritance FBFB FWFW FWFW FBFB FBFBFBFB FBFWFBFW FBFWFBFW FWFWFWFW 25% black fur 50% brown fur 25% white fur The result would be…

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16. Codominance Inheritance Sometimes a heterozygous individual will have a phenotype that isn’t a complete mix of the parental traits. Instead, the offspring will express both traits of the parents at the SAME TIME. codominance When this happens it is called codominance.

17. Codominance Inheritance Let’s look at an example. F R = allele for red roses F W = allele for white roses What happens if we make the following cross? F R F R FWFWFWFW X

18. Codominance Inheritance FRFR FRFR FWFW FWFW FRFWFRFW FRFWFRFW FRFWFRFW FRFWFRFW Once again, all of the offspring have a heterozygous genotype.

19. Codominance Inheritance The phenotype in this case would be roses that are red with white markings (or white with red markings).

20. Codominance

21. Codominance Inheritance Intermediate and codominance are similar because they both produce a third phenotype when heterozygous. They are different because intermediate shows a blend or mix of the parent traits. While codominance can produce both parent traits simultaneously.

22. P1/P2 F1

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25. Polygenic Inheritance We’ve already seen the effects of dominance-only(simple), intermediate, and codominance inheritance.

26. Polygenic Inheritance However, none of them can explain a trait such as human skin color with so many different variations.

28. Polygenic Inheritance Or different oak trees that produce various amounts of acorns.

29. Polygenic Inheritance The only way to get such large variation is to have multiple genes controlling the trait. Human height is just such an example of polygenic inheritance. Let’s say height is controlled by three hypothetical genes: A, B, & C.

30. Polygenic Inheritance A person with the genotype AABBCC would be very tall. A person with the genotype aabbcc would be very short.

31. Polygenic Inheritance A person with AABBCc would be taller than someone with AABbCc. The combinations of phenotypes increases with the number of genes that affect that trait.

32. Polygenic Inheritance The result is a very large number of combinations (Some characters are even affected by dozens of genes!)

34. First Iris Layer Pigment AA = Produce lots of pigment Aa = Produce some pigment aa = Do not produce pigment Second Iris Layer Pigment BB = Produce lots of pigment Bb = Produce some pigment bb = Do not produce pigment

35. Environmental Influence The genotype does not always predict an individual’s phenotype. Many times the environment has a strong impact on how the genes get expressed. Example: Koreans (both North and South) all share the same common ancestry.

36. Environmental Influence North Korean children are on average much shorter. Why the difference?

37. Environmental Influence 38 th Parallel

38. Environmental Influence Malnutrition is widespread in N. Korea due to a repressive government. This variation in diet has lead to a difference in phenotype (height) that is not genetically based.

39. Environmental Influence This means that many genes are not rigidly set. The amount of gene expression is largely dependent on an individual’s environment.

40. Arctic Fox Winter Fur Summer Fur

41. Sex-Linked Inheritance A normal human has 23 pairs of chromosomes in each of his/her cells. The last pair are called sex chromosomes.

42. Sex-Linked Inheritance Females have two X chromosomes.

43. Sex-Linked Inheritance Males have one X chromosome and one Y chromosome.

44. Sex-Linked Inheritance The X chromosome is much larger than the Y chromosome.

45. Sex-Linked Inheritance Therefore, more genes are found on the X chromosome than the Y chromosome. Males, having only one X chromosome, are more likely to express sex-linked disorders. Let’s use a real example to see why.

46. Sex-Linked Inheritance Human red-green colorblindness is a sex- linked trait that is controlled by a recessive gene found on the X chromosome.

47. Sex-Linked Inheritance N = non-color blind allele n = color blind allele A woman with either the genotype X N X N or X N X n would have normal vision. A woman with X n X n would be colorblind.

48. Sex-Linked Inheritance Males, however, can only have X N Y or X n Y since the gene is not found on the Y chromosome. X N Y = normal vision male X n Y = colorblind male

49. Sex-Linked Inheritance Here’s an example. A non-colorblind male and a heterozygous female (called a “carrier”) are going to have a child. Are they likely to have a colorblind child?

50. Sex-Linked Inheritance XnXn XNXN XNXN Y XNXNXNXN XNYXNY XnYXnY Male = X N,Y Female = X N,X n XNXnXNXn Color Blind Male Non-color blind carrier female Non-color blind female and male

51. Sex-Linked Inheritance The predicted results… This couple has a 0% chance of having a colorblind daughter. However, half of their sons are expected to be colorblind.

52. Check For Understanding