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” and “n” alleles obtained and record in the chart. Do not count the genes in the graveyard. Calculate the new gene frequency for the remaining population.
x. Once counted, place all the genes from the surviving yaks back into the gene pool. Do not include the genes from the graveyard. The gene pool will be shrinking during the activity. xi. Repeat steps 4-10 three more times (until a fourth generation has been born and counted.)

IV. Data table:
Gene Frequencies and Natural Selection Data Table genotypes drawn genes remaining V. Graph:

VI. Calculations:

My results did not support my hypothesis because I said that by the fourth generation there would be no mutation left but there was. An environment where the frequency change would be different would be in and environment that was hot because then the yaks would not need fur. The set-up of the gene pool was completely unrealistic because the genes are not always an even amount of the same genes. We know that natural selection was the cause of the shift in frequencies because there was no random mating, no new mutations, they did not migrate, and the population was even. The frequency of the mutated gene will reach zero over a long period of time.

References: http://en.wikipedia.org/wiki/Natural_selection http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html
Mrs. K’s Yak Lab Handout

References: http://en.wikipedia.org/wiki/Natural_selection http://www.globalchange.umich.edu/globalchange1/current/lectures/selection/selection.html Mrs. K’s Yak Lab Handout