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?
Bellringer – March 13, 2014
G= Green g= white White = 13% = 0.13 = gg= q2
√0.13=√q2
A) q = 0.36 then p = 0.64B) GG = p2= (0.64)2=0.4096= 40.96% Gg = 2pq= 2(0.64)(0.36)=0.4608= 46.08% gg = q2= (0.36)2= 0.1296= 12.96%C) (.4608)(200) = 92 turtles are heterozygous
ANSWER KEY
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?
Practice Problem #2
AA = 110, Aa = 350; aa = 40. AA = 110/500 = 0.22; Aa=350/500 = 0.70 ; aa=
40/500= 0.08 A=110 + 110 + 350 = 570/1000 = 0.57; a = 40 + 40 + 350 = 160/1000 = 0.43
A) Actual population
p=A= PTC taster q= a = PTC non-taster 40/500= 0.08 = PTC non-taster = aa= q2
√0.08=√q2
q = 0.28 then p = 0.72 RR = p2 = (0.72)2 = 0.52 = 52.00% Rr = 2pq = 2(0.72)(0.28) = 0.40= 40.00% rr = q2 = (0.28)2 = 0.08 = 8.00%
b) Hardy-weinberg
Evolution and Zygotic Barriers (Macroevolution
part 2)
Ms. KimH. Biology
1. Geographic isolation2. Reproductive barriers (isolation)3. Change in chromosome numbers
through mutation4. Adaptive radiation (example of
divergent evolution)
Speciation = formation of NEW species
Why don’t similar species interbreed??
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
http://bcs.whfreeman.com/thelifewire/content/chp24/2402001.html
http://www.pbs.org/wgbh/nova/evolution/evolution-action-salamanders.html
Reproductive Isolationbiological 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 WinterLate Summer
Courtship rituals and other behaviors unique to a species are effective barriers
Sympatric: Behavioral Isolation
http://wps.aw.com/bc_campbell_biology_7/26/6661/1705356.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
Polyploidy
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