Card Lab: a Population Genetics Simulation Exercise
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How-To-Do-It | Card Lab: A Populaton Genetcs Simulation Exercise Christopher M. Easton Population genetics labs in introduc- the small population could not even longer contribute alleles directly to the tory laboratory manuals usually rely sustain itself, and numbers continued next generations. This age structure is Downloaded from http://online.ucpress.edu/abt/article-pdf/59/8/518/48275/4450369.pdf by guest on 29 September 2021 on jars filled with different colored to decline. Eventually, the remaining similar to that observed with insects beads from which students draw their wild condors were captured, and a which produce large numbers of eggs, breeding population (McCourt 1983; zoo-based breeding program begun, in have a high juvenile mortality, and Dolphin 1992). This type of lab as- an attempt to rebuild a population suf- die shortly after laying eggs as adults. sumes that all individuals drawn are of ficient to maintain itself in the wild. The age structure is also similar to reproductive age. In an actual popula- A population bottleneck also ran- many populations undergoing explo- tion, a range of ages is represented. domly samples alleles from the general sive growth, where the number of in- Populations can be divided into ju- population. Frequently rare alleles are dividuals beyond reproductive age is a veniles (too young to reproduce), indi- lost, reducing the variability of the minute fraction of the total. viduals or reproductive age, and indi- population (Hartl 1980). After the bot- The traditional 'sex' of the face cards viduals that are senescent (too old to tleneck, the diminished effective popu- was preserved, resulting in 16.66% of breed). The senescent organisms have lation size is now vulnerable to the the females being reproductive age, already passed on their alleles, and will effects of genetic drift. More rare alleles while 33.33% of the males are of repro- not do so again. However, the juveniles may be lost, reducing the genetic diver- ductive age. This would seem to be an that will become reproductive and the sity of the population even further. unusual and artificial distribution, but reproductive-age individuals ulti- The reduced diversity may become does characterize human populations mately determine which alleles can be evident as normally recessive and det- in the U.S. and other countries with passed on to the next generations. rimental alleles are expressed in a moderate population growth. Human A precipitous decline in population majority of the remaining population females have a finite reproductive life number (population bottleneck) typi- (inbreeding effects). For example, chee- span and then enter a period of post- cally impacts all ages, with no guaran- tahs were reduced by an unknown reproductive life. In contrast, males can tee that the surviving individuals will catastrophe about 10,000 years ago and remain reproductive throughout their be of reproductive age. If few repro- again by human hunting during the physiological life span, assuming good ductive individuals survive the bottle- 19th and early 20th centuries to a hand- health. Thus, the males have as much neck, the effective population size ful of small breeding populations in as twice the reproductive life span as (Hartl 1980; Hill 1972; Felsenstein South Africa (Campbell 1990). This bot- females, and may, conceivably, consti- 1971), and therefore population fecun- tleneck resulted in decreased general tute twice the reproductive population dity, will be reduced for several breed- fecundity, little genetic variability, and in some countries. In fact, 1985 data ing seasons. In this way, a population high susceptibility to disease. Similar indicate that as much as 70% of the bottleneck may be projected through congenital problems are evident in a males and 40% of the females are of several generations, even after the en- number of domestic dog breeds in reproductive age in highly developed vironmental conditions that imposed it which inbreeding is a common prac- countries, like the United States and have been ameliorated. tice. Sweden (Solomon et al. 1993). Such has been the plight of the Cal- Card lab demonstrates how a popu- Card lab also demonstrates the ef- ifornia condor. Hunting and DDT re- lation bottleneck impacts genetic diver- fects of migration, mutation and selec- duced the numbers to only a few re- sity and even survival of a population. tion on the allelic frequency and diver- maining in the wild. Although DDT It uses a standard deck of playing cards sity of a population. Card lab may was banned and the condors protected, to show how the age structure of a stand alone or supplement "bead labs" population can magnify the effect of a and computer simulations, which offer bottleneck by restricting reproduction more diverse choices for allelic fre- Christopher M. Easton is an Adjunct over several seasons. quency. Instructorin the Department of Biol- The face cards of the deck were cho- Lab Procedures ogy at Tompkins Cortland Commu- sen to represent the reproductive aged nity College and a Ph.D. student in the Department of Biological Sci- individuals purely for the simplicity in Students were given a lab handout, ences at Binghamton University,Bing- recognizing them. The remaining cards which not only provided basic instruc- hamton, NY 13902-6000, e-mail: represent juveniles. Individuals be- tions for the lab, but also asked leading [email protected]. yond reproductive age are not in- questions to stimulate thought and dis- cluded in this model because they no cussion about results. Students were 518 THEAMERICAN BIOLOGY TEACHER, VOLUME 59, NO. 8, OCTOBER1997 encouraged to work in pairs or small single mated pair colonize a new area, reduced by population bottlenecks. groups, and to actively discuss their starting a new population. Approximatelyhalf the students using answers. In addition to the lab hand- Each suit (hearts,spades, diamonds, this lab immediately extrapolated to out, student groups needed a standard clubs) in the deck represents a genetic analyzing the age structure of initial deck of 52 playing cards and a calcula- variant (allele) of the population. Aces deals that did not contain reproductive tor. represent infants of both sexes. Even age individuals. Most of these students The lab handout is reproduced be- numbers (2, 4, 6, 8, 10, Q) represent assumed that a '10' would require one low as part of the text. Generalanswers females, but only the Queens are of breeding season to reach reproductive are provided immediately following reproductive age. Odd numbers (3, 5, age. They then looked at the numberof each question or set of questions.These 7, 9, J, K) represent males, with Jacks reproductive individuals available for answers may be readily derived from and Kings being reproductive age. the next five seasons, realizing that the the concepts and principles described Laterin the semesterwe may make use single bottleneck would thus be pro- in any introductorylevel text (e.g. So- of the age structureand introduce dif- jected through several generations of lomon et al. 1993; Campbell 1990). ferential reproduction between Jacks the population. The remaining stu- Some concepts were not mentioned in and Kings, but for now they may be dents required additional coaching to the lab handout, but were emphasized considered identical. realize the severity of the effect they to the students during lab as each had created.Discussions of population group reached certain points in the Questions for the Students genetics and microevolutionfollowing exercise. This fostered communication 1) What is the frequency of each this lab reinforced the concepts, and between individual students, the genetic variant(suit) in the population? integratedthem into the frameworkof Downloaded from http://online.ucpress.edu/abt/article-pdf/59/8/518/48275/4450369.pdf by guest on 29 September 2021 group, and the instructor. It also al- This simply requires dividing the evolutionarybiology. lowed the instructorto assess individ- numberof cardsin each suit (13)by the ual participationwithin the group. total number of cards in the deck (52), 13/52 = 1/4 = 0.25 for each suit. PartII: The Number of Caution to Instructors 2) What percent of the population is SurvivorsNeeded To Individuals from foreign countries of reproductiveage? or from strict religious backgrounds This requirescounting the face cards Avoid a Boffleneck may lack any exposure to playing (12) and again dividing by the total Instructions cards. Instructorsshould be prepared number of cards (12/52 = 0.23), then to explain some fundamentals,such as multiplying by 100% to convert the Using trial and repetition,determine what a suit is, what a face card is, and frequency to a percentage (23%). your answers to the following two how to shuffle, without embarrassing questions.You should be able to repeat the student. Instructions your result in order to call it consistent. The following rules shall apply to One method to assure this is to shuffle deal Introduction to Population this lab: A) Females may mate with and the cards, counting the cards Genetics only one male. B) Hybridization will until the stated requirementsare met. Write down this number. Shuffle the Population genetics is a study of the preserve both genetic variants. To simulate a population bottleneck: cardsback into the deck and repeatthis distribution of genes and alleles (pos- a total of 10 times. Shuffle the cards well, then deal 10 process Then,calcu- sible alternategene forms) within pop- late the mean (average), mode (most ulations. Population geneticists also cards face up. Record your results by writing down the face value and suit of frequent), and median (middle in a study the circumstancesthat alter the ranked of 10 each card dealt. Repeat this procedure list) your counts. [Instruc- distribution, such as mutation, migra- tor's note: Instructorsshould be two more times, shuffling dealt cards pre- tion, selection,and genetic drift.A pop- cal- back into the deck each time.