Sandy colored mouse –2 copies of same allele (sandy) Black colored –At least one copy of black allele
Mutation Rate Mutation rate = 2 mutations per 10 9 sites in DNA Possible sites = 10 Diploid organism has 2 copies of the gene Now multiply it all: 2 x 10 -9 x 2 = 4 x 10 -8 But what does this number mean?
This Number Means Something 4 x 10 -8 can also be seen as a fraction 1/25,000,000 So 1 out of every 25 million mice will have a mutation that gives rise to a black coat Wow, sounds like this will never happen! We don’t have all the info yet –We need to factor time and breeding into the equation
Determining the Rate of Change Reproductive rate = 5 offspring per year Population has 5000 breeding females Calculate the total offspring per year 5 x 5000 = 25,000 per year Hmm, that number still doesn’t mean much to me Remember 1/25,000,000? Multiply! –1/25,000,000 x 25,000 = 1/1000 –That’s one black mouse every 1000 years
Rate of Change and Time Big deal, one black mouse every thousand years. How’s that going to do anything for evolution? The lava flows in this mouse’s habitat are 17,000,000 years old That means this variation could have happened 1700 times since those flows appeared! Only once was needed
Natural Selection Natural selection took care of the rest