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The Case of Fur Color Evolution in Beach Mice or Slide Set Available from

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1 The Case of Fur Color Evolution in Beach Mice or Slide Set Available from

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. Image adapted from: 273_F1.html Melanocyte cells

4 Image:

5

6 Hair Color Two pigments – Eumelanin – Pheomelanin Image adapted from: 273_F1.html Eumelanin Roland Mattern Pheomelanin Roland Mattern Melanocyte cells

7 Hair Color Dark Hair: Lots of eumelanin Fair Hair: More pheomelanin, less eumelanin Red Hair: Lots of pheomelanin

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

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 Image from: c(tyr) Tyrp1 Tyrp2 p

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 MC1R stimulation leads to lots of cAMP production which means Tyrp1, Tyrp2 and p are expressed  lots of eumelanin. Image from: c(tyr) Tyrp1 Tyrp2 p

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 Inadequate MC1R stimulation leads to less cAMP production which means Tyrp1, Tyrp2 and p are not expressed  less eumelanin; more pheomelanin. Image from: c(tyr) Tyrp1 Tyrp2 p

12 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. Image from: c(tyr) Tyrp1 Tyrp2 p

13 Eumelanin and Pheomelanin Images from:

14 The Natural History of Fur Color in Beach Mice 1.0

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

16 Fur Color Subspecies: leucocephalus trissyllepsis allophrys/peninsula ris ammobates subgriseus 1.2

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

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

19 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? 1.6

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

22 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.

23 Consequence of Mutation There is a change in the the amino acid identity at position #67: an Arginine vs. a Cysteine 4.6 Amino Acid Sequence Dark Fur: MPTQGPQKRLLGSLNSTSTATPHLGLATNQTGPWCLQVS I PDGLFLSLGLVSLVENV LVVIAITKN R NLHSPMYSFICCLALSDLMVSISLVLETAIILLLEAGALVTRAALVQQLD NVIDVLICGSMVSSLCFLGVIAIDRYISIFYALRYHSIVTLPRARRAIXGIWVASIFFSTLFI TYYNHTAVLICLVTFFLAMLALMA X LYVHMLTRAYQHAQGIAQLQKRQGSTXQGFCL KGA X TLTIILGIFFLCWGPFFLHLTLIVLCPQHPTCSCI FKNFNLYLVLIIFSSIVDPLIYAFRSQELRMTLREVLLCSW Amino Acid Sequence Light Fur: MPTQGPQKRLLGSLNSTSTATPHLGLATNQTGPWCLQVSVPDGLFLSLGLVSLVEN VLVVIAITKN C NLHSPMYSFICCLALSDLMVSISLVLETAIILLLEAGALVTRAALVQQL DNVIDVLICGSMVSSLCFLGVIAIDRYISIFYALRYHSIVTLPRARRAIVGIWVASIFFSTL FITYYNHTAVLICLVTFFLAMLALMA I LYVHMLTRAYQHAQGIAQLQKRQGSTRQGFC LKGAATLTIILGIFFLCWGPFFLHLTLIVLCPQHPTCSCI FKNFNLYLVLIIFSSIVDPLIYAFRSQELRMTLREVLLCSW

24 Freeman 4e Fig. 15.4

25 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.

26 mc1r Gene 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’

27 mc1r Gene 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.

28 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 4.7

29 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. 4.9

30 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. 5.1

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

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

33 Observable Relationship: Genes vs. Fur Color There are three possible genotypes associated with the mc1r gene: 1.RR  Arginine-Arginine: Indicates that both copies of chromosome 16 have an arginine amino acid at position #67 of the mc1r gene. + Eumelanin 5.4

34 Observable Relationship: Genes vs. Fur Color There are three possible genotypes associated with the mc1r gene: 1.RR  Arginine-Arginine: Indicates that both copies of chromosome 16 have an arginine amino acid at position #67 of the mc1r gene. + Eumelanin 2.CC  Cysteine-Cysteine: Indicates that both copies of chromosome 16 have a cysteine amino acid at position #67 of the mc1r gene. - Eumelanin 5.4

35 Observable Relationship: Genes vs. Fur Color There are three possible genotypes associated with the mc1r gene: 1.RR  Arginine-Arginine: Indicates that both copies of chromosome 16 have an arginine amino acid at position #67 of the mc1r gene. + Eumelanin 2.CC  Cysteine-Cysteine: Indicates that both copies of chromosome 16 have a cysteine amino acid at position #67 of the mc1r gene. - Eumelanin 3.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 5.4

36 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 = ? 5.5

37 House Mouse Karyotype (Mus musculus) Chromosome 8 is approx. 130,000,000 bp

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

39 Observable Relationship: Scoring System

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

41 Observable Pattern: All Body Parts RR Individuals Body Part Rostrum Whisker Cheek Eyebrow Ear Ventrum Ankle RC Individuals CC Individuals Average Color Scores for: Average Hoekstra et al a

42 RR Individuals Body Part Rostrum Whisker Cheek Eyebrow Ear Ventrum Ankle RC Individuals CC Individuals Average Color Scores for: Average b Question: What does the above table tell you? Does it confirm or refute a genetic basis for differences in fur color among mice?

43 Questions: There is a clear pattern: beach mice with the RR genotype tend to be darker than those with the RC or CC genotype. 1.Why is the average score for RR mice score less than 2 for most body parts? 2.Why is the average score for CC mice greater than 0 for most body parts? 3.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. 5.10

44 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. 1.Strongly Agree 2.Agree 3.Unsure/Confused 4.Disagree 5.Strongly Disagree 5.11

45 Predict Allele Frequencies ___% R ___% C ___% R ___% C ___% R ___% C ___% R ___% C ___% R ___% C ___% R ___% C 5.12a

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

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

48 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. Ancestral Inland Population Present-day Beach Population Present-day Inland Population Time

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

50 The Ecology of Fur Color in Beach Mice 2.0

51 Beach Mouse Food Facts: 2.1

52 Hunting Style of Predators Sight and Sound Hunters Taste/Smell Hunter 2.2

53 Predator-Prey Experiment (The Advantage of Fur Color) 2.3

54 Predator-Prey Experiment (The Advantage of Fur Color) Owls catch dark mouse first 64% of the time Owls catch light mouse first 36% of the time. Owls catch dark mouse first 37% of the time Owls catch light mouse first 63% of the time. 2.4

55 Regional Pattern: Fur Color and Habitat Color -Researchers examined fur color in nine beach mouse populations. -Fur color brightness was significantly correlated to soil brightness where each population lived. 2.5

56 Predation Study – Clay Mice (A) Two locations with different color soil where predation on clay mice was tested. (B) Most attacks in light soil environments were on dark mice; most attacks in dark soil environments were on light mice. 2.6

57 Attack on a Clay Mouse 2.6b

58 Summary Evidence suggests that fur color may have evolved as a result of selective predation. Fur coloration matching the habitat coloration leads to less detection by predators and increases the odds of successful reproduction. 2.7

59 Clicker Q1 The C  T substitution at position 199 of the mc1r gene: A.arose by a mutation in the beach mouse populations in response to a need for protection from predation. B.leads to the failure of melanocytes to make an MC1R protein. C.arose by a mutation then increased in frequency because it was selectively advantageous in the beach mouse populations. D.had no effect on the beach mouse populations. E.produced an alternate allele that was detrimental to mice on the white sand beaches 6.6

60 Clicker Q2 What was the reason for the lighter coat colors of the mice on the white sand beaches? A.Owls and other carnivores prey on beach mice that do not carry the mutant allele. B.A substitution of cysteine for arginine at position 67 of the MC1R protein. C.A substitution of thymine for cytosine at position 199 of the mc1r gene nucleotide sequence. D.The failure of melanocytes to lay down melanin pigment in the cortex of hairs of the lighter colored beach mice. E.The poorer binding affinity for α-MSH and the lower amount of cAMP produced by individuals with the mutated MC1R protein. 6.7


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