 A scientist has studied the amount of PTC tasters in a population. PTC tasting is dominant. From one population, 500 individuals were sampled. The scientist found the following individuals: AA = 110, Aa = 350; aa = 40.  Calculate the genotypic and allelic frequencies for the PTC gene at this population.  Determine the genotypic and allelic frequencies expected at Hardy-Weinberg equilibrium using the homozygous recessive. Is this population in Hardy-Weinberg equilibrium? Is the population evolving?

 AA = 110, Aa = 350; aa = 40.  AA = 110/500 = 0.22; Aa=350/500 = 0.70 ; aa= 40/500= 0.08  A= = 570/1000 = 0.57;  a = = 160/1000 = 0.43

 p=A= PTC taster q= a = PTC non-taster  40/500= 0.08 = PTC non-taster = aa= q 2  √0.08=√q 2  q = 0.28 then p = 0.72  RR = p 2 = (0.72) 2 = 0.52 = 52.00%  Rr = 2pq = 2(0.72)(0.28) = 0.40= 40.00%  rr = q 2 = (0.28) 2 = 0.08 = 8.00%

 Green color (G) is dominant to white color (g) in turtles.  In a population of 200 turtles, 13% are white. A) What are the allele frequencies? B) What percentage of each genotype are in this population? C) How many turtles are heterozygous?

 G= Greeng= white  White = 13% = 0.13 = gg= q 2  √0.13=√q 2 A) q = 0.36 then p = 0.64 B) GG = p 2 = (0.64) 2 =0.4096= 40.96%  Gg = 2pq= 2(0.64)(0.36)=0.4608= 46.08%  gg = q 2 = (0.36) 2 = = 12.96% C) (.4608)(200) = 92 turtles are heterozygous

Ms. Kim H. Biology

1. Geographic isolation 2. Reproductive barriers (isolation) 3. Change in chromosome numbers through mutation 4. Adaptive radiation (example of divergent evolution)  Speciation = formation of NEW species

A. harrisi A. leucurus Hello over there Geographic Isolation

Two general modes of speciation determined by the way gene flow among populations is initially interrupted: Geographic and Reproductive Isolation Speciation can occur in two ways: ◦ Geographic: Allopatric speciation (means “other”)  a genetic isolation WITH a geographical barrier; new group isolated from its parent population ◦ Reproductive: Sympatric speciation (means “together”)  genetic isolation WITHOUT a geographical barrier; a reproductive barrier isolates population in SAME habitat

Allopatric speciation Sympatric speciation eeman.com/the lifewire/content /chp24/ html

Reproductive Isolation  biological factors (barriers) that stop 2 species from producing viable, fertile hybrids  Two types of barriers ◦ Postzygotic “after the zygote”  Zygote can NOT develop ◦ Prezygotic “before the zygote”  Sperm and egg can not fuse

Pre-Zygotic Barriers

 2 species encounter each other rarely, or not at all, because they live in different habitats, even though not isolated by physical barriers Sympatric: Habitat Isolation

 Species that breed at different times of the day, different seasons, or different years cannot mix their gametes Sympatric: Temporal Isolation Late Winter Late Summer

 Courtship rituals and other behaviors unique to a species are effective barriers Sympatric: Behavioral Isolation m/bc_campbell_ biology_7/26/66 61/ cw/ index.html

 Morphological differences can prevent successful mating  Related species may attempt to mate but CAN’T  anatomically incompatible  Sperm = transfer Sympatric: Mechanical Isolation Mating organs don’t fit

 Sperm of one species may not be able to fertilize eggs of another species  Ex: specific molecules on egg coat adhere to specific molecules on sperm Sympatric: Gametic Isolation

Post-Zygotic Barriers

 Genes of the different parent species may interact and impair the hybrid’s development  Hybrids are very weak and/or underdeveloped Reduced Hybrid Viability Salamander hybrid shows incomplete development

 Even if hybrids may live and be strong, they may be sterile Reduced Hybrid Fertility

 Polyploidy is presence of EXTRA sets of chromosomes due to accidents during cell division ◦ ex: “nondisjunction”  It has caused the evolution of some plant species  More common in plants than in animals