Is it Natural Selection? Key Beak Depth in Darwin's Finches

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1 Teacher Guide Is it Natural Selection? Key Beak Depth in Darwin's Finches Checklist item or? Evidence and tes Change over time Mean beak depth was greater in the offspring that were born after the drought. Variability Individuals have different beak depths. Heritability Beak depth in offspring resembles (has a positive relationship to) that of the parents. (inferred) Individuals with greater beak depth survived, presumably because they were able to eat larger seeds. Therefore, they were more likely to reproduce. Beak depth in finch parents and their offspring 11 Mean beak depth (mm) Parents (x) Offspring (y) Offspring s mean beak depth (mm) Parents mean beak depth (mm) 2016 University of Utah Updated March 20,

2 Horn Length in Bighorn Sheep Checklist item or? Evidence and tes Change over time Mean horn length decreased over 30 years of study. Variability Individuals have different horn lengths. Heritability Horn length of sons resembles that of their fathers. Hunters selectively harvested rams with longer horns, making rams with smaller horns more likely to reproduce. 1. Calculate the mean horn length for all of the rams: total horn length number of rams 2. Calculate the mean horn length for the rams that were harvested: total horn length number of rams 968 cm 14 rams 307 cm 4 rams 69 cm 77 cm Horn lengths of 5-year-old rams in 1989 and if they were eventually harvested Horn length (cm) Harvested? 2016 University of Utah Is it Natural Selection? Teacher Guide 2

3 Mold Resistance in Irish Lumper Potatoes Checklist item or? Evidence and tes Change over time potatoes were resistant before or after the blight all that were exposed died. Variability All plants were genetically identical clones. Heritability Mold resistance comes from an allele of the R1 gene, which passes from parents to offspring. Offspring (clones) had the same alleles as the parents. All of the potatoes were vulnerable to infection, so ne were more likely to reproduce. te: This example shows how a population with very low genetic diversity is vulnerable to extinction Vlnerable Resistant 2016 University of Utah Is it Natural Selection? Teacher Guide 3

4 Shell Length in Freshwater Snails Checklist item or? Evidence and tes Change over time In this example, we see evidence. Variability Individuals have different shell lengths. Heritability Longer shell length is associated with presence of crayfish in the water, t with the shell length of the parents. When they are present, crayfish eat the smaller snails, making the larger snails more likely to reproduce. Snail parents NC NC C C Water source NC stream C stream NC stream C stream Mean shell length (mm) Mean shell length (mm) NC parents NC water NC parents C water C parents NC water C parents C water 2016 University of Utah Is it Natural Selection? Teacher Guide 4

5 Eye span in stalk-eyed flies Checklist item or? Evidence and tes Change over time Fossilized stalk-eyed flies had shorter eye spans than stalk-eyed flies that are living today. Variability Individuals have different relative eye spans. Heritability Eye span/body length of sons resembles that of their fathers. Males with longer eye spans are more likely to get to mate. Relative eye span of stalk-eyed fly fathers and sons 1.40 Fathers (x) Sons (y) eye span body length mean eye span body length Sons mean eye span/body length Father s eye span/body length 2016 University of Utah Is it Natural Selection? Teacher Guide 5

6 Malaria Resistance in People in Uganda Checklist item or? Evidence and tes Change over time We can infer change over time, because the Hb S allele is much more common in the Ugandan population than it is in the rest of the world. Variability People in the population have different combinations of the Hb and Hb S alleles, which make some people resistant to malaria and others t resistant. Heritability Hb alleles pass from parents to offspring. People with one copy of the Hb S allele are more likely to survive malaria, reach reproductive age, and have children of their own. Alleles Hb/Hb (n-carrier) Hb/Hb S (carrier) Children with malaria Children without malaria Total number of children % of children with malaria TOTAL n-carriers (Hb / Hb) Carriers (Hb / Hb S ) 2016 University of Utah Is it Natural Selection? Teacher Guide 6

7 Color Blindness in Pingalapese People Checklist item or? Evidence and tes Change over time Color blindness is more common today than it was in the past. Variability People in the population have different combinations of working and n-working CNGB3 alleles, which make some people color blind, some carriers of the n-working allele, and some n-carriers. Heritability CNGB3 alleles pass from parents to offspring. We see evidence that people's CNGB3 allele combination or color blindness makes some individuals more likely to reproduce than others. te: This is an example of the founder effect, which is a type of genetic drift. Time Color blind Carrier Unaffected Total After the 1775 typhoon 5 % 95 % 100% Today 5 % 3 65 % 100% After the 1775 typhoon Today Unaffected Carrier Color blind Unaffected Carrier Color blind 2016 University of Utah Is it Natural Selection? Teacher Guide 7