Question

1. Describe the connections between the following causal factors (in no specific order) for the evolution of mice with lighter coat coloration on white sand beaches:
2. 1. Owls and other carnivores prey on beach mice that do not carry the mutant allele.
   2. A substitution of cysteine for arginine at position 67 of the MC1R protein.
   3. A substitution of thymine for cytosine at position 199 of the mc1r gene nucleotide sequence.
   4. The failure of melanocytes to lay down melanin pigment in the cortex of hairs of the lighter colored beach mice.
   5. The poorer binding affinity for α-MSH and the lower amount of cAMP produced by individuals with the mutated MC1R protein.

Answer 1

a.Owls and other carnivores prey on beach mice that do not carry the mutant allele. :Mouse that do not carry the mutant allele have a dark coat color dur to deposition of eumelanin pigment in their hair cortex and being dark colored ,they are easily identified by predators such as owl and other carnivores that fed on them.

b.A substitution of cysteine for arginine at position 67 of the MC1R protein :When this substitution occurs,the MC1R protein fails to bind to α-MSH; hence no cAMP produced and biosynthetic pathway is hindered and eumelanin is not produced ;hence no color in mouse.

c.A substitution of thymine for cytosine at position 199 of the mc1r gene nucleotide sequence. :This mutation type occured in the the beach mouse populations in response to their need for protection from being attacked by owls.As a result of this mutation, melanocytes fail to make to make an MC1R protein( that stimulates cAMP production that in turn activates synthesis of (tyr), Tyrp1, Tyrp2 )•When cAMP is produced less, c(tyr), Tyrp1, Tyrp2 and p are not as readily expressed and hence no pigment is produced.

d.The failure of melanocytes to lay down melanin pigment in the cortex of hairs of the lighter colored beach mice.Hair color is present due to production of eumelanin in the hair follicle melanocytes. When MC1R protein becomes non-functional,no  eumelanin is produced and hence no eumelanin pigment is present in the cortex of hairs of light colored beach mouse.So, they are white colored.

e.The poorer binding affinity for α-MSH and the lower amount of cAMP produced by individuals with the mutated MC1R protein.With poorer binding affinity, the biosynthetic pathway for eumelanin production is hindered.No,cAMP is produced and therefore c(tyr), Tyrp1, Tyrp2 and p expression is also reduced and hence all together eumelanin production is prevented and no pigment is laid down in the cortex of hair of light colored beach mice.