1. Complex Patterns of Inheritance

2. 1.Incomplete dominance 2.Codominance 3.Multiple alleles 4.Sex linked inheritance 5.Polygenic inheritance

3. Incomplete Dominance Inheritance pattern where the phenotype of a heterozygote is intermediate between those of the two homozygotes Homozygous Red Flower X Homozygous White Flower RR rr Heterozygous Pink Flower Rr

4. Incomplete Dominance ParentOffspringParent

5. Codominance Inheritance pattern where phenotypes of both homozygote parents are equally expressed in the heterozygous offspring Black Feathered ChickensWhite Feathered Chickens X BB bb Homozygous Recessive Homozygous Dominant

6. Codominance Inheritance pattern where phenotypes of both homozygote parents are equally expressed in the heterozygous offspring Black Feathered ChickensWhite Feathered Chickens X BB bb Homozygous Recessive Homozygous Dominant Checkered Feathered Chickens Bb

7. Codominance: phenotypes of both homozygote parents are equally expressed in the heterozygous offspring BB Bb bb

8. Multiple Alleles -Traits controlled by more than two alleles are said to have multiple alleles. -Although an offspring can only inherit two alleles for one trait, sometimes more than two alleles exist for that one trait

9. Examples of a gene that has multiple alleles:

10. Polygenic Inheritance The inheritance pattern of a trait that is controlled by two or more genes -Traits controlled by polygenic inheritance include those that have a wide range of variation.

11. Examples of traits that are controlled by polygenic inheritance:

14. Polygenic Inheritance Example: -Stem length in a plant is controlled by three different genes: A, B, and C -Each gene is on a different chromosome and has two alleles, so each diploid plant has six total alleles for stem length -A plant that is homozygous for short alleles at all three locations (aabbcc) will be 4 in tall, while a plant homozygous for tall alleles (AABBCC) will be 16 in tall -The existence of each tall gene gives the plant 2 inches in height

15. Polygenic Inheritance The inheritance pattern of a trait that is controlled by two or more genes -In polygenic inheritance, each allele represented by an uppercase letter contributes a small but equal portion to the trait being expressed.

16. Polygenic Inheritance When one trait is controlled by more than two genes.

17. Sex-linked Inheritance (-Sex determination: -Autosomes: The 1 st - 22 nd pairs of homologous chromosomes in somatic cells -Sex chromosomes: the 23 rd pair of chromosomes which determine the sex of the individual -Sex chromosomes found in females: XX -Sex chromosomes found in males: XY)

18. Sex-linked Inheritance -Sex linked traits: traits controlled by genes found on sex chromosomes -The alleles for sex-linked traits are written as superscripts of the X or Y chromosome: X R X r or X R Y -Just like normal alleles, each parent will pass on one of two possible sex chromosomes to the offspring. Mom can pass on X R or X r Dad can pass on X R or Y

29. Complex Patterns of Inheritance 1.Incomplete dominance 2.Codominance 3.Multiple alleles 4.Sex linked inheritance 5.Polygenic inheritance

30. Environmental Influences of Gene Expression -External environmental influences (temperature, nutrition, light, chemicals) can affect gene expression -Internal environmental influences (hormones) also affect gene expression

31. Complex Inheritance of Human Traits 1.Codominance in humans Sickle-Cell Anemia 2.Multiple Alleles in humans Blood type 3.Sex linked Traits in Humans Color Blindness Hemophilia 4.Polygenic Inheritance in humans Skin color 5.Changes in Chromosome Numbers Down Syndrome

32. Codominance in Humans Example: Sickle Cell Anemia -If you cross a homozygous normal with a homozygous sickle cell, the offspring will have both normal and sickle celled red blood cells -The offspring will exemplify codominance because it will express the phenotypes of both parents equally

33. Multiple Alleles in Humans Example: Blood typing -Possible blood types: A, B, AB, O -The I gene determines blood type -There are three alleles for the I gene: I A, I B, i I A I A or I A i = Type A blood I B I B or I B i = Type B blood I A I B = Type AB blood ii = Type O blood

34. Sex-linked Traits in Humans Example: Hemophilia -Much more frequent in males than females -Men need to inherit only one recessive hemophilia allele for them to express the disease -Women need to inherit two recessive hemophilia alleles to express the disease *SIMILAR TO HEMOPHILIA: COLOR BLINDNESS

35. Polygenic Inheritance in Humans Example: Skin Pigmentation -Skin pigmentation in humans is controlled by four genes -The range of possible skin shades can be shown in a bell shaped curve

36. Changes in Chromosome Numbers: Example: Down Syndrome: (Trisomy 21) -Occurs as the result of the presence of an extra 21 st chromosome

37. Changes in Chromosome Numbers: Example: Down Syndrome: (Trisomy 21) -Occurs as the result of the presence of an extra 21 st chromosome -Karyotype: a chart of chromosome pairs valuable in identifying unusual chromosome numbers in cells

38. Complex Patterns of Inheritance 1.Incomplete dominance 2.Codominance 3.Multiple alleles 4.Sex linked inheritance 5.Polygenic inheritance