Question 3 What unit best describes estimates of evolutionary rate? substitutions/site/year substitutions/site mutations/year alleles/year
Added by Dale C.
Close
Step 1
Step 1: Evolutionary rate is the rate at which mutations occur in a population over time. Show more…
Show all steps
Your feedback will help us improve your experience
Madhur L and 97 other Biology educators are ready to help you.
Ask a new question
Labs
Want to see this concept in action?
Explore this concept interactively to see how it behaves as you change inputs.
Key Concepts
Recommended Videos
Two species differ at 15 positions in a protein sequence of 120 amino acids. If these species diverged 20 million years ago, what is the rate of substitution. Please give your answer as the number substitutions per site per million years correct to six decimal places.
Madhur L.
4.2 Two lineages separated 10 million years ago and differ at 50 of 780 nucleotides What is the rate of substitution for the locus? What is the substitution rate per site at this locus?
Narayan H.
Researchers sequenced 420 nucleotides from a human and a mouse that code for 140 amino acids that are part of a larger protein. These two taxa split 96 million years ago. By comparing the two sequences, they found 45 synonymous and 5 nonsynonymous differences. Assume all of these are substitutions. They calculate that 80% of all mutations would be non-synonymous and the remainder synonymous. The potential/expected number of synonymous (S) and nonsynonymous (N) sites are then obtained as S = 420 x 0.2 = 84 and N = 420 x 0.8 = 336. a) Calculate the proportion of synonymous (pS) and nonsynonymous differences (pN). [1] b) For species separated by so many years, observed mutations will often affect the same codon, leaving uncertainty as to which happened first. Depending on the sequence of mutations, the same mutation could be counted as nonsynonymous or synonymous. We will ignore this complication here. Estimate the number of synonymous (dS) and nonsynonymous (dN) substitutions per site using the Jukes-Cantor correction as: dS = -3log(1 - (4pS/3)) and dN = -3log(1 - (4pN/3)) Note that this is now differences per site, rather than per gene. [1] c) What is the rate of synonymous and nonsynonymous substitutions? Use the equations: r = dS / S and r = dN / N which are the same as equation 8.3 except that we have already divided by the number of nucleotides (L - 84 and 336, respectively) when we calculated pS and pN, and doing so again would be incorrect. [1] d) If we assume that the nonsynonymous mutations can be divided into two classes: a) having no fitness effect and b) being lethal, what percentage of nonsynonymous mutations can be considered lethal? You have to assume that the synonymous rate = neutral mutation rate and then use rN = (1-α)μ. [1]
Adi S.
Recommended Textbooks
Biology for AP Courses
Objective Biology for NEET
Introduction to General, Organic and Biochemistry
Transcript
Watch the video solution with this free unlock.
EMAIL
PASSWORD