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The Case of Fur Color Evolution in Beach Mice or

Slide Set Available from www.evo-ed.com. The Case of Fur Color Evolution in Beach Mice or. http:// www.evo-ed.com. Wouldn’t it be nice if I had white fur???. Anatomy of a Hair Follicle. The hair shaft is made of cornified cells – that is, dead cells filled with keratin.

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The Case of Fur Color Evolution in Beach Mice or

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  1. Slide Set Available from www.evo-ed.com The Case of Fur Color Evolution in Beach Miceor http://www.evo-ed.com

  2. Wouldn’t it be nice if I had white fur???

  3. Anatomy of a Hair Follicle • The hair shaft is made of cornified cells – that is, dead cells filled with keratin. • Within the region of matrix stem cells are specialized pigment-producing melanocyte cells. Melanocyte cells Image adapted from: http://www.nature.com/ng/journal/v38/n3/fig_tab/ng0306-273_F1.html

  4. Image: http://www.dermnetnz.org/doctors/principles/images/hair-bulb.gif

  5. Hair Color • Two pigments • Eumelanin • Pheomelanin Melanocyte cells Pheomelanin Roland Mattern Eumelanin Roland Mattern Image adapted from: http://www.nature.com/ng/journal/v38/n3/fig_tab/ng0306-273_F1.html

  6. Hair Color • Dark Hair: Lots of eumelanin • Fair Hair: More pheomelanin, less eumelanin • Red Hair: Lots of pheomelanin

  7. How is melanin produced? • Transmembrane proteins that are stimulated by a hormone. • When these melanocortin receptor proteins are stimulated…. LOTS of eumelanin is produced.

  8. Stimulation of MC1R leads to lots of cAMP production. • cAMP leads to the expression of at least four genes: c(tyr), Tyrp1, Tyrp2, p c(tyr) Tyrp1 Tyrp2 p Image from: http://www.sciencedirect.com/science/article/pii/S0021967307010199

  9. Stimulation of MC1R leads to lots of cAMP production. • cAMP leads to the expression of at least four genes: c(tyr), Tyrp1, Tyrp2, p • MC1R stimulation leads to lots of cAMP production which means Tyrp1, Tyrp2 and p are expressed lots of eumelanin. c(tyr) Tyrp1 Tyrp2 p Image from: http://www.sciencedirect.com/science/article/pii/S0021967307010199

  10. Stimulation of MC1R leads to lots of cAMP production. • cAMP leads to the expression of at least four genes: c(tyr), Tyrp1, Tyrp2, p • Inadequate MC1R stimulation leads to less cAMP production which means Tyrp1, Tyrp2 and p are not expressed  less eumelanin; more pheomelanin. c(tyr) Tyrp1 Tyrp2 p Image from: http://www.sciencedirect.com/science/article/pii/S0021967307010199

  11. Stimulation of MC1R leads to lots of cAMP production. • cAMP leads to the expression of at least four genes: c(tyr), Tyrp1, Tyrp2, p • MC1R is a pretty big deal. c(tyr) Tyrp1 Tyrp2 p Image from: http://www.sciencedirect.com/science/article/pii/S0021967307010199

  12. Eumelanin and Pheomelanin Images from: www.chem.sc.edu/analytical/chem107/lab4_032205.pdf

  13. 1.0 The Natural History ofFur Color in Beach Mice

  14. 1.1 Fact Sheet: Peromyscuspolionotus • Common names: Beach Mouse or Old Field Mouse. • Location: Southeastern U.S.A. • Habitat: Sand burrows in dunes or old fields. • Home-range: ~1000 m2 • Breeding: Monogamous pair-bonding. Litters of 2-8 pups, every 30 days. • Lifespan: 9-12 months.

  15. 1.2 Fur Color Subspecies: leucocephalus trissyllepsis allophrys/peninsularis ammobates subgriseus

  16. 1.3 How are populations of these sub species distributed within the range of the Beach Mouse? ? ? ? ? ?

  17. 1.5 The Spatial Distribution of Fur Color Lighter colored sub-species live on light sand beaches; darker colored sub-species live in darker habitat.

  18. 1.6 Question Assuming that ancestral populations of beach mice had dark brown fur, what could have happened to explain the occurrence of light-colored coastal sub-species?

  19. The Melanocortin-1-Receptor (MC1R) • What can you tell me about the MC1R protein? • Write three things down.

  20. The Melanocortin-1-Receptor (MC1R) • What can you tell me about the MC1R protein? • Write three things down. • Do you think there are any differences between the MC1R protein of dark haired mice and the MC1R protein of light haired mice? If so, what? • Write something down.

  21. The Melanocortin-1-Receptor (MC1R) • What can you tell me about the MC1R protein? • Write three things down. • Do you think there are any differences between the MC1R protein of dark haired mice and the MC1R protein of light haired mice? If so, what? • Write something down. • Do you think there are any differences between the mc1r allele of dark haired mice and the mc1r allele of light haired mice? • Write something down.

  22. 4.6 Consequence of Mutation There is a change in the the amino acid identity at position #67: an Arginine vs. a Cysteine Amino Acid Sequence Dark Fur: MPTQGPQKRLLGSLNSTSTATPHLGLATNQTGPWCLQVSIPDGLFLSLGLVSLVENVLVVIAITKNRNLHSPMYSFICCLALSDLMVSISLVLETAIILLLEAGALVTRAALVQQLDNVIDVLICGSMVSSLCFLGVIAIDRYISIFYALRYHSIVTLPRARRAIXGIWVASIFFSTLFITYYNHTAVLICLVTFFLAMLALMAXLYVHMLTRAYQHAQGIAQLQKRQGSTXQGFCLKGAXTLTIILGIFFLCWGPFFLHLTLIVLCPQHPTCSCI FKNFNLYLVLIIFSSIVDPLIYAFRSQELRMTLREVLLCSW Amino Acid Sequence Light Fur: MPTQGPQKRLLGSLNSTSTATPHLGLATNQTGPWCLQVSVPDGLFLSLGLVSLVENVLVVIAITKNCNLHSPMYSFICCLALSDLMVSISLVLETAIILLLEAGALVTRAALVQQLDNVIDVLICGSMVSSLCFLGVIAIDRYISIFYALRYHSIVTLPRARRAIVGIWVASIFFSTLFITYYNHTAVLICLVTFFLAMLALMAILYVHMLTRAYQHAQGIAQLQKRQGSTRQGFCLKGAATLTIILGIFFLCWGPFFLHLTLIVLCPQHPTCSCI FKNFNLYLVLIIFSSIVDPLIYAFRSQELRMTLREVLLCSW

  23. Freeman 4e Fig. 15.4

  24. Substitution Mutation • A single nucleotide substitution mutation in the mc1r gene causes a change in amino acid #67 in the MC1R protein chain. • When amino acid #67 is cysteine, the MC1R protein is unable to effectively bind the α-MSH. This changes the pigment pathway and eumelanin is not produced.

  25. mc1rGene Sequence Let’s look at what happens when ONE SPECIFIC nucleotide is changed…. 5’-ATGCCCACCCAGGGGCCTCAGAAGAGGCTTCTGGGTTCTCTCAACTCCACCTCCACAGCC ACCCCTCACCTTGGACTGGCCACAAACCAGACAGGGCCTTGGTGCCTGCAGGTGTCTGTC CCGGATGGCCTCTTCCTCAGCCTGGGGCTGGTGAGTCTGGTGGAGAATGTGCTGGTCGTG ATAGCCATCACCAAAAACCGCAACCTGCACTCGCCCATGTATTCCTTCATCTGCTGTCTG GCCCTGTCTGACCTGATGGTGAGTATAAGCTTGGTGCTGGAGACGGCTATCATCCTGCTG CTGGAGGCAGGGGCCCTGGTGACCCGGGCCGCTTTGGTGCAACAGCTGGACAATGTCATT GACGTGCTCATCTGTGGCTCCATGGTGTCCAGTCTTTGCTTCCTTGGTGTCATTGCCATA GACCGCTACATCTCCATCTTCTATGCATTACGTTATCACAGCATTGTGACGCTGCCCCGG GCACGACGGGCCATCGTGGGCATCTGGGTGGCCAGCATCTTCTTCAGCACCCTCTTTATC ACCTACTACAACCACACAGCCGTCCTAATCTGCCTTGTCACTTTCTTTCTAGCCATGCTG GCCCTCATGGCAATTCTGTATGTCCACATGCTCACCCGAGCATACCAGCATGCTCAGGGG ATTGCCCAGCTCCAGAAGAGGCAGGGCTCCACCCGCCAAGGCTTCTGCCTTAAGGGTGCT GCCACCCTTACTATCATTCTGGGAATTTTCTTCCTGTGCTGGGGCCCCTTCTTCCTGCAT CTCACACTCATCGTCCTCTGCCCTCAGCACCCCACCTGCAGCTGCATCTTTAAGAACTTC AACCTCTACCTCGTTCTCATCATCTTCAGCTCCATCGTCGACCCCCTCATCTATGCTTTT CGGAGCCAGG AGCTCCGCATGACACTCAGGGAGGTGCTGCTGTGCTCCTGGTGA- 3’

  26. mc1rGene Sequence Let’s look at what happens when ONE SPECIFIC nucleotide is changed…. 5’-ATGCCCACCCAGGGGCCTCAGAAGAGGCTTCTGGGTTCTCTCAACTCCACCTCCACAGCC ACCCCTCACCTTGGACTGGCCACAAACCAGACAGGGCCTTGGTGCCTGCAGGTGTCTGTC CCGGATGGCCTCTTCCTCAGCCTGGGGCTGGTGAGTCTGGTGGAGAATGTGCTGGTCGTG ATAGCCATCACCAAAAACTGCAACCTGCACTCGCCCATGTATTCCTTCATCTGCTGTCTG GCCCTGTCTGACCTGATGGTGAGTATAAGCTTGGTGCTGGAGACGGCTATCATCCTGCTG CTGGAGGCAGGGGCCCTGGTGACCCGGGCCGCTTTGGTGCAACAGCTGGACAATGTCATT GACGTGCTCATCTGTGGCTCCATGGTGTCCAGTCTTTGCTTCCTTGGTGTCATTGCCATA GACCGCTACATCTCCATCTTCTATGCATTACGTTATCACAGCATTGTGACGCTGCCCCGG GCACGACGGGCCATCGTGGGCATCTGGGTGGCCAGCATCTTCTTCAGCACCCTCTTTATC ACCTACTACAACCACACAGCCGTCCTAATCTGCCTTGTCACTTTCTTTCTAGCCATGCTG GCCCTCATGGCAATTCTGTATGTCCACATGCTCACCCGAGCATACCAGCATGCTCAGGGG ATTGCCCAGCTCCAGAAGAGGCAGGGCTCCACCCGCCAAGGCTTCTGCCTTAAGGGTGCT GCCACCCTTACTATCATTCTGGGAATTTTCTTCCTGTGCTGGGGCCCCTTCTTCCTGCAT CTCACACTCATCGTCCTCTGCCCTCAGCACCCCACCTGCAGCTGCATCTTTAAGAACTTC AACCTCTACCTCGTTCTCATCATCTTCAGCTCCATCGTCGACCCCCTCATCTATGCTTTT CGGAGCCAGG AGCTCCGCATGACACTCAGGGAGGTGCTGCTGTGCTCCTGGTGA- 3’ The Cytosine at position 199 has now changed to a Thymine.

  27. 4.7 Consequence of Mutation The specific amino acid sequence is very important. One mutation within the sequence can have affect how the protein interacts with the melanocyte-stimulating hormone (α-MSH). Amino Acid #67 = Arginine Amino Acid #67 = Cysteine

  28. 4.9 The Role of the MC1R Protein When amino acid #67 is cysteine, the MC1R protein is unable to effectively bind the α-MSH. This changes the pigment pathway and eumelanin is not produced.

  29. 5.1 Plausible Mechanism; Observable Pattern • In biological research, to say that something at the molecular or genetic level is responsible for a phenotypic trait, a plausible mechanism and an observable relationship should be identified.

  30. 5.2 Mechanism: Alleles of mc1r Gene • The mc1r gene has two alleles: AlleleC [Cysteine at pos #67] Codes for a non-functional MC1R protein. AlleleR [Arginine at pos #67] Codes for a functional MC1R protein. The genetic code for these two alleles differs by a single nucleotide substitution.

  31. 5.4 Observable Relationship:Genes vs. Fur Color • There are three possible genotypes associated with the mc1r gene:

  32. 5.4 Observable Relationship:Genes vs. Fur Color • There are three possible genotypes associated with the mc1r gene: • RR  Arginine-Arginine: Indicates that both copies of chromosome 16 have an arginine amino acid at position #67 of the mc1r gene. + Eumelanin

  33. 5.4 Observable Relationship:Genes vs. Fur Color • There are three possible genotypes associated with the mc1r gene: • RR  Arginine-Arginine: Indicates that both copies of chromosome 16 have an arginine amino acid at position #67 of the mc1r gene. + Eumelanin • CC Cysteine-Cysteine: Indicates that both copies of chromosome 16 have a cysteine amino acid at position #67 of the mc1r gene. - Eumelanin

  34. 5.4 Observable Relationship:Genes vs. Fur Color • There are three possible genotypes associated with the mc1r gene: • RR  Arginine-Arginine: Indicates that both copies of chromosome 16 have an arginine amino acid at position #67 of the mc1r gene. + Eumelanin • CC Cysteine-Cysteine: Indicates that both copies of chromosome 16 have a cysteine amino acid at position #67 of the mc1r gene. - Eumelanin • RC  Arginine-Cysteine: Indicates that one copy of chromosome 16 has an arginine amino acid on position #67 of the mc1r gene; the other copy has a cysteine in position #67 of the mc1r gene. ? Eumelanin

  35. 5.5 Observable Relationship:Genes vs. Fur Color • Is there a relationship between the fur color of beach mouse individuals and the allele combinations (genotypes) they possess? CC homozygous = ? RR homozygous = ? RC heterozygous = ?

  36. House Mouse Karyotype (Musmusculus) Chromosome 8 is approx. 130,000,000 bp

  37. 5.6 Observable Pattern: Color Scoring Ear Rostrum Eyebrow Whiskers Cheek Ankle Ventrum

  38. 5.7 Observable Relationship: Scoring System 2 1 2 1 2 1 1 0 0 2 0 1 0 2 0 0

  39. 5.8 Observable Pattern:Rostrum Color Mice with the genotype RR have the darkest rostrum color.

  40. 5.9a Observable Pattern: All Body Parts Average Color Scores for: Body Part Rostrum Whisker Cheek Eyebrow Ear Ventrum Ankle RR Individuals 2.00 1.42 1.28 1.83 1.13 0.91 1.06 RC Individuals 1.81 1.00 1.25 1.54 0.80 0.55 0.82 CC Individuals 0.81 0.45 0.69 0.79 0.28 0.00 0.29 1.38 Average 0.47 1.11 Hoekstra et al 2006

  41. 5.9b Average Color Scores for: Body Part Rostrum Whisker Cheek Eyebrow Ear Ventrum Ankle RR Individuals 2.00 1.42 1.28 1.83 1.13 0.91 1.06 RC Individuals 1.81 1.00 1.25 1.54 0.80 0.55 0.82 CC Individuals 0.81 0.45 0.69 0.79 0.28 0.00 0.29 1.38 Average 0.47 1.11 Question: What does the above table tell you? Does it confirm or refute a genetic basis for differences in fur color among mice?

  42. 5.10 Questions: There is a clear pattern: beach mice with the RR genotype tend to be darker than those with the RC or CC genotype. • Why is the average score for RR mice score less than 2 for most body parts? • Why is the average score for CC mice greater than 0 for most body parts? • RC mice are closer in fur color to RR mice than CC mice. Does this mean that R is dominant over C? Be prepared to explain your answer.

  43. 5.11 Question:Differences in fur color among beach mouse populations can be fully explained by the relative frequency of C and R alleles present within each population. • Strongly Agree • Agree • Unsure/Confused • Disagree • Strongly Disagree

  44. 5.12a Predict Allele Frequencies ___% R ___% C ___% R ___% C ___% R ___% C ___% R ___% C ___% R ___% C ___% R ___% C

  45. 5.12b Actual Allele Frequencies 100% R 0% C 30% R 70% C 70% R 30% C 95% R 5% C 5% R 95% C 100% R 0% C

  46. 5.13 Fur color differences among beach mouse sub-species (i.e. populations) cannot be fully explained by differences in R:C allele frequencies. Why not?

  47. In Class Exercise on Mouse Evolution Scenario: Start with an ancestral, inland population in which all individuals have dark fur. The ancestral population evolves, resulting in one population that is still inland, and another that now lives on the beach. Present-day Inland Population Ancestral Inland Population Present-day BeachPopulation Time

  48. In Class Exercise on Mouse Evolution:Questions for Student Teams to Consider • When did the ancestral population live? How big was it (number of individuals)? • What were the mc1r genotype frequencies? The mc1r allele frequencies? • How big is the present day inland population (number of individuals)? • What are the mc1r genotype frequencies? The mc1r allele frequencies? • How big is the present day beach population (number of individuals)? • What are the mc1r genotype frequencies? The mc1r allele frequencies? • Where along the timeline did an R  C substitution in MC1R occur?

  49. 2.0 The Ecology ofFur Color in Beach Mice

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