NOTES: 11.3

1. NOTES: 11.3 Exceptions to Mendelian Genetics!

2. Beyond Dominant and Recessive Alleles ● Some alleles are neither dominant nor recessive, and many traits are controlled by multiple allelesORmultiple 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

3. 1. Incomplete Dominance ● 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?...

5. Incomplete Dominance R = RED R’ = white ● P: RR x R’R’ ● F1: what is the F1 generation going to look like (phenotype)? ●F2: what is the F2 generation going to look like (phenotype)? Do the crosses now in your notes

6. Incomplete Dominance R R R’ R’ • R = Red R’ = White • P: RR x R’R’ • F1: all RR’ (all pink) • F2: 1 Red: 2 Pink: 1 White RR’ RR’ RR’ RR’ Which allele is dominant in pink offspring?……….neither R R’ **notice the ratio for incomplete dominance 1:2:1 RR RR’ red pink RR’ R’R’ pink white R R’

8. 2. CoDominance! ● 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.

10. What is the difference between incomplete dominance and codominance? • Incomplete 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

11. What is the difference between incomplete dominance and codominance? • Codominance= 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.

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

13. 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.

14. 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

15. 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.

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

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

18. wild type (C): chinchilla (cch): 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. himalayan (ch): albino (c):

19. Awww…..

20. Multiple Alleles… ● Example 2: Human Blood Types: 3 alleles (IA, IB, i) -Phenotypically Type A Blood (genotype = IAIA or IAi) -Phenotypically Type B Blood (genotype = IBIB or IBi) -Phenotypically Type AB Blood (genotype = IAIB) -Phenotypically Type O Blood (genotype = i i)

22. 4. Polygenic Traits ● 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

23. 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.)

24. 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

25. 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:

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:10 cm • AabbCc:8 cm • AABBCc:14 cm

27. 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)

28. 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!

29. 4. Polygenic Traits • 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)

31. 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

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

33. 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

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

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

37. 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

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

40. 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

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

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

43. CROSS #1: Female genotype:XR XR Male genotype:Xr Y

44. PUNNETT SQUARE:

45. PUNNETT SQUARE:

46. CROSS #1: Offspring genotype ratio: 2 XR Xr :2 XR Y Offspring phenotype ratio: 2 red-eyed females : 2 red-eyed males

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

48. CROSS #2: Female genotype:XR Xr Male genotype:XR Y

49. PUNNETT SQUARE:

50. PUNNETT SQUARE: