Yak Lab

Yak Lab

Natural selection is the process by which favorable heritable traits become more common in successive generations of a population of reproducing organisms, and unfavorable heritable traits become less common. Natural selection acts on the phenotype, or the observable characteristics of an organism, such that individuals with favorable phenotypes are more likely to survive and reproduce than those with less favorable phenotypes. If all the offspring that organisms can produce were to survive and reproduce, they would soon overrun the earth. Darwin illustrated this point by a calculation using elephants. “The elephant is reckoned the slowest breeder of all known animals, and I have taken some pains to estimate its probable minimum rate of natural increase; it will be safest to assume that it begins breeding when 30 years old and goes on breeding until 90 years old; if this be so, after a period from 740 to 750 years there would be nearly 19 million elephants descended from this first pair."

I. Purpose:

The purpose of this lab was to simulate natural selection.

II. Materials:

Paper bag

White beans, “N” shaggy fur

Brown beans, “n” no fur

3 Petri dishes

III. Methods:

i. Obtain a gene pool containing 50 normal genes (N) and 50 defective genes (n).

ii. Record and calculate the initial frequencies on the data chart. Write a hypothesis above the data table that predicts what will happen to the frequency of the defective gene over four generations.

iii. Label one Petri dish “N” and one “n”. Label the third dish “graveyard”.

iv. Shake the bag containing all the genes in order to “mate” the yaks in the population.

v. Blindly select two beans at a time and record the genotype of the newborn yak on your data chart under “NN”, “Nn”, or “nn”.

vi. If the yak born has no hair (nn), put both genes in the graveyard. This yak has died and these genes (beans) will not be counted nor used again.

vii. If the yak born is has hair (NN or Nn), sort the dominant (N) and recessive (n) alleles into the correct Petri dishes.

viii. Continue to draw out genes until all the yaks in the bag have been born.

ix. Count and record the total number of “N”