Population Genetics

BBS 1134 GENETICS LAB EXERCISE Population Genetics Objectives 1. To enable student to understand how to determine allele and genotype frequencies in a population in Hardy-Weinberg equilibrium. 2. To demonstrate the effect of one generation of migration on allele and genotype in the conglomerate generation. 3. To study the effect of one generation of selection on allele and genotype frequencies. Introduction Hardy-Weinberg Equilibrium states that under certain conditions, after one generation of random mating, the genotype frequencies at a single gene locus will become fixed at a particular equilibrium value. The conditions are: • Infinite population size (or sufficiently large so as to minimize the effect of genetic drift. • No natural selection. • No mutation. • No migration/gene flow. • Random mating within a single population. • Is sexually reproducing, either monoecians & dioecian. Material Yellow (Dhal bean), White (Soy bean), Black (black pepper) Experiment Autosomal Allele 1. 100 Dhal beans and 20 black peppers were prepared, mixed together. 2. The seeds were randomly paired. 3. The results obtained were examined. 4. Step 1 to 3 was repeated to examine F2. T: p T: q

= 100/200 = 0.83 = 20/200 = 0.17

Results F1 Generation Genotype

Observed

Expected

TT Tt tt Total

41 17 2 60

p² (60) = 41 2pq (60) = 17 q² (60) = 2 60

(Obs-Exp)² Exp 0 0 0 0

F2 Generation Genotype

Observed

Expected

TT Tt tt Total

39 21 0 60

p² (60) = 41 2pq (60) = 17 q² (60) = 2

(Obs-Exp)² Exp 0.098 0.941 2.00 3.039

Form the result, x2, were obtained, it shows that it follows the Hardy-Weinberg equilibrium. Multiple Allele 1. 100 Dhal beans, 50 soy bean and 20 black peppers were prepared and mixed together. 2. The seeds were randomly paired up. 3. The result obtained was examined. IA : black IA = (20/170)  p= 0.118 IB: white IB = (50/170) q = 0.29 l: yellow l = (100/170)r = 0.59 Results Genotype

Observed

IA IA

2

IA i

8

IB IB

8

IB i

26

IA IB

9

ii

32

TOTAL

85

Expected (0.12)2 (85) =1 2(0.12) (0.59) = 12 (0.29)2 (85) =7 2(0.29) (0.59) (85) = 29 2(0.120 (0.29) (85) =6 (0.59)2 (85) = 30

(Obs- Exp)2 Exp 1.000 1.333 0.143 0.310 1.500 0.133

From the result, we can conclude that the Hardy-Weinberg equilibrium is followed.

Migration 75

pd = 0.8 qd = 0.2

pr = 0.2 qr = 0.8

pd = 160 yellow qd = 40 white

pr = 40 yellow pr = 160 white

1. 160 Dhal beans (yellow) and 40 soy beans (white) were prepared and mixed together to represent the donor. 75 seeds from donor were transferred up to recipient.

2. Seeds were randomly paired up from the conglomerate population and the results were examined. Results Allele frequencies in recipient population

Initial genotype frequencies

New allele frequencies in conglomerate population

p = 0.2 (yellow)

p² = 0.04

Pc = (72/250)

q = 0.8 (white)

2pq = 0.32 q² = 0.64

New genotype frequencies in conglomerate p² = 0.083 2pq = 0.410

Qc = (178/250)

q² = 0.507

From the results obtained, we can conclude this generation obeys the Hardy-Weinberg equilibrium. Natural Selection 1. 100 Dhal beans and 100 soy beans were prepared and mixed together. 2. Beans were randomly paired. 3. Lethal alleles (heterozygous) were eliminated and the remaining alleles were counted. 4. From the F1 generation, the seeds were mixed and randomly paired up. 5. The F2 generation alleles were counted and the results were examined. 100 yellow (WAA) 100 white (Waa) Lethal gene (WAa)

Results Allele Frequencies

A = p : 0.5

a = q : 0.5

Original Genotype Frequencies WAA = (30/100)

Allele Frequencies After Selection

Genotype Frequencies After Selection

P = [(2x30)/(2x10)] = 0.30

WAA = (17/55) = 0.31 WAa= (25/55) = 0.45

WAa = (45/100)

Waa = (25/100)

q = [(2x25)/(2x100)] = 0.25

Waa = (13/55) = 0.24

0.55

1.00

From the results obtained, F1 generation and F2 generation obey the Hardy-Weinberg equilibrium. Discussion Migration occurs when living things organization move from one biome to another. In most cases organisms migrate to avoid local shortages of food, usually caused by winter or overpopulation. Animals may also migrate to certain location to breed, as is in the case with some fish. Effect of migration in population: • The allele frequencies in the gene pool change. • Causing evolution. • Gene flow can hinder optimal adoption of a population to local condition. • Recurrent migration can maintain a disadvantages trait at high frequency. Selection is the evolutionary process by which favorable traits that are heritability become more common in successive generations of a population of reproducing organisms, and unfavorable traits that are heritable become less common. Effect of selection in population: • Decrease the frequency of harmful mutation (stabilizing selection) • Increase the frequency of beneficial mutation (directional selection). • New organisms through evolution. • Organisms become better adapted to their environment (increase in fitness of the individual)

Conclusion 1. The understanding of how to determine the allele and genotype frequencies in a population of Hardy-Weinberg was achieved. 2. The effect of one generation of migration on allele and genotype frequencies in a conglomerate generation was demonstrated 3. The effect to one generation of selection on allele and genotype frequency was studied.