2. NOTES: 11.3 Exceptions to Mendelian Genetics!

3. Beyond Dominant and Recessive Alleles ● Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles OR multiple genes. ● Examples of genes that are different than being totally “Dominant” or “Recessive:” 1. Incomplete dominance 2. Codominance 3. Multiple Alleles 4. Polygenic Traits 5. Environmental Influences 6. Sex-Linked Inheritance

4. ● One allele is NOT completely dominant over another. -The heterozygous phenotype is somewhere between the 2 homozygous phenotypes. What does this mean? ● Mendel crossed a homozygous red plant with a homozygous white plant. ● What do you think would be the expected results?...

6. R = REDR’ = white ● P: RR x R’R’ ● F 1 : what is the F1 generation going to look like (phenotype)? ● F 2 : what is the F2 generation going to look like (phenotype)? Do the crosses now in your notes

7. R = RedR’ = White P: RR x R’R’ F 1 : all RR’ (all pink) F 2 : 1 Red: 2 Pink: 1 White **notice the ratio for incomplete dominance 1:2:1 R R’ RR’ Which allele is dominant in pink offspring?……….neither R R’ R R’ RR RR’ red pink RR’ R’R’ pink white

9. ● Definition: BOTH alleles for a trait contribute to the phenotype of the organism. ● Examples: -The alleles for red (RR) and white (WW) hair in cattle are co-dominant.  Cattle with both alleles have brown/white patterning or roan (RW). -In certain varieties of chickens the alleles for black and white feathers are co-dominant.  Chickens with both alleles appear speckled.

11. What is the difference between incomplete dominance and codominance? Incomplete dominanceIncomplete dominance = heterozygous phenotype is somewhere in between the 2 homozygous phenotypes. For example, in (RR’), the R’ allele is not active, but R cannot produce its full effect when it is combined with R’. RR = red RR’ = pink R’R’ = white 1:2:1 ratio for F2 generation

12. What is the difference between incomplete dominance and codominance? CodominanceCodominance = heterozygous phenotype has characteristics of both alleles for that trait. … –BOTH alleles are active and are expressed together (both act like dominant genes). For example, cross between red hair (RR) and white hair (WW), the calf will be roan (RW) both red and white hairs.

13. RR = red WW = white RW= red & white

14. Incomplete Dominance: Remember: Incomplete Dominance in the form of an example like this: RED Flower x WHITE Flower  PINK Flower With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a totally different from the parental traits.

15. Codominance ”Co-" is "together". –Cooperate = work together –Coexist = exist together In COdominance, the "recessive" & "dominant" traits appear together in the phenotype of hybrid organisms. remember codominance in the form of an example like this: red x white  red & white hair

16. Codominance With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which BOTH of the parental traits appear together.

17. ● Definition: Genes with more than two alleles ● Remember: YOU only inherit TWO alleles (one from mom, one from dad)

18. ● Example 1: -in rabbits, coat color is determined by a single gene with four alleles.

19. wild type (C): chinchilla (c ch ): himalayan (c h ): albino (c): There are four possible alleles for coat color in rabbits. This does not mean that an individual can have more than two alleles but that there are more than 2 possible alleles that can exist in a population.

20. Awww…..

21. Multiple Alleles… ● Example 2: Human Blood Types: 3 alleles (I A, I B, i) -Phenotypically Type A Blood (genotype = I A I A or I A i ) -Phenotypically Type B Blood (genotype = I B I B or I B i ) -Phenotypically Type AB Blood (genotype = I A I B ) -Phenotypically Type O Blood (genotype = i i )

23. ● Traits that are controlled by two or more genes ● Examples: –Stem length in some plants; –Eye color in fruit flies is controlled by three genes; –Human skin color is controlled by more than 4 different genes; –Shows a wide range of phenotypes as result

24. Example: STEM LENGTH ● suppose stem length in a plant is controlled by 3 different genes: A, B, and C ● each diploid plant has 2 alleles for each gene (e.g. AaBBcc OR aaBbCc, etc.)

25. Example: STEM LENGTH ● a plant homozygous for short alleles for all 3 genes (aabbcc) might grow to 4 cm ● a plant homozygous for TALL alleles for all 3 genes (AABBCC) might grow to 16 cm

26. Example: STEM LENGTH ● the difference in heights is 12 cm (or, 2 cm per each of the 6 tall alleles)… ● you could say that each “uppercase” allele contributes 2 cm to the total plant height… SO, predict the phenotypes for the following genotypes:  AaBbCc:  AabbCc:  AABBCc:

27. Example: STEM LENGTH ● the difference in heights is 12 cm (or, 2 cm per each of the 6 tall alleles)… ● you could say that each “uppercase” allele contributes 2 cm to the total plant height… SO, predict the phenotypes for the following genotypes:  AaBbCc:10 cm  AabbCc:8 cm  AABBCc:14 cm

28. Example: STEM LENGTH ● so, if you crossed a TALL 16 cm plant (AABBCC) with a short 4 cm plant (aabbcc), all of the F1 plants would be: Genotype: AaBbCc Phenotype: intermediate height (10 cm)

29. Example: STEM LENGTH ● THEN, if you let 2 F1 plants cross, you would see a broad range of heights in the F2 ● if you counted the different phenotypes, they could be represented with a “bell curve” – a typical pattern see with POLYGENIC INHERITANCE!

30. Human skin color is controlled by 4 different genes Dark skinned people have “uppercase” alleles that code for melanin at all gene positions for skin color. Lighter skinned people have few gene positions with alleles that code for melanin (in other words, they have more “lower case” alleles for those genes)

32. 5) Environmental Influences: ● as an organism develops, many factors can influence how the gene is expressed, OR even whether the gene is expressed at all ● influences can be EXTERNAL or INTERNAL

33. EXTERNAL INFLUENCES: Examples: Temperature Nutrition Light (e.g. shade or sunlight for plant leaf size) Chemicals / pH Infectious agents

34. INTERNAL INFLUENCES: ● the internal environments of males and females are different because of hormones and structural differences ● Examples: -horn size in mountain sheep -male-pattern baldness in humans -feather color in peacocks

36. INTERNAL INFLUENCES: ● could also include AGE (although the effects of age on gene expression are not well understood)

37. SEX DETERMINATION: (CH 14) ● RECALL: in humans, the diploid # of chromosomes is 46 (23 pairs) ● of the 23 pairs, 22 are AUTOSOMES, and the 23 rd pair represents the SEX CHROMOSOMES ● human females: XX ● human males: XY

38. SEX DETERMINATION: ● Males (XY) can produce 2 kinds of gametes:  sperm cells carrying X  sperm cells carrying Y ● Females (XX) will only produce “X” gametes

39. SEX DETERMINATION: ● so the odds of having a boy or girl are always 50/50:

41. 6) SEX-LINKED INHERITANCE: (CH 14) ● SEX-LINKED TRAITS = traits controlled by genes located on sex chromosomes ● the alleles are written as superscripts of the X and Y chromosome ● Y-linked traits are passed only from male to male ● since males only have 1 X chromosome, if there is a gene on the X chromosome, males only get 1 copy

42. 6) SEX-LINKED INHERITANCE: Example: eye color in fruit flies -the gene for eye color is on the X chromosome -RED eyes are dominant: X R -white eyes are recessive: X r

43. CROSS #1: homozygous red-eyed female X white-eyed male **change in your notes!

44. CROSS #1: Female genotype:X R X R Male genotype:X r Y

45. PUNNETT SQUARE: XRXR XRXR X r Y

46. PUNNETT SQUARE: XRXR XRXR X r X R X r YX R Y

47. CROSS #1: Offspring genotype ratio: 2 X R X r : 2 X R Y Offspring phenotype ratio: 2 red-eyed females : 2 red-eyed males

48. CROSS #2: heterozygous red-eyed female X red-eyed male

49. CROSS #2: Female genotype:X R X r Male genotype:X R Y

50. PUNNETT SQUARE: XRXR XrXr X R Y

51. PUNNETT SQUARE: XRXR XrXr X R X R X r YX R YX r Y

52. CROSS #2: Offspring genotype ratio: 1 X R X R : 1 X R X r : 1 X R Y : 1 X r Y Offspring phenotype ratio: 2 red-eyed females : 1 red-eyed male : 1 WHITE-EYED MALE