Download Zygotic Barriers (Macro 2)

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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?
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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
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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%
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?
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G= Green
g= white
 White = 13% = 0.13 = gg= q2
 √0.13=√q2
A) q = 0.36 then p = 0.64
B) 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
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Ms. Kim
H. Biology
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Geographic isolation
Reproductive barriers (isolation)
Change in chromosome numbers through
mutation
Adaptive radiation (example of divergent
evolution)
Speciation = formation of NEW species
Hello over
there 
A. harrisi
A. leucurus
Geographic 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
http://bcs.whfr
eeman.com/the
lifewire/content
/chp24/24020
01.html
Allopatric speciation
Sympatric speciation
http://www.pbs.org/wgbh/nova/evolution/evolution-action-salamanders.html
biological factors (barriers) that stop
2 species from producing viable,
fertile hybrids
 Two types of barriers
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◦ Postzygotic “after the zygote”
 Zygote can NOT develop
◦ Prezygotic “before the zygote”
 Sperm and egg can not fuse
Pre-Zygotic
Barriers
Sympatric: Habitat
Isolation
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2 species encounter each other rarely, or
not at all, because they live in different
habitats, even though not isolated by
physical barriers
Sympatric: Temporal
Isolation
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Species that breed at different times of the
day, different seasons, or different years
cannot mix their gametes
Late Summer
Late Winter
Sympatric: Behavioral
Isolation
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Courtship rituals and other behaviors
unique to a species are effective barriers
http://wps.aw.co
m/bc_campbell_
biology_7/26/66
61/1705356.cw/
index.html
Sympatric: Mechanical
 Morphological
Isolation
differences can
prevent successful
mating
 Related species
may attempt to
mate but CAN’T
anatomically
incompatible
 Sperm = transfer
Mating organs don’t fit
Sympatric: Gametic
Isolation
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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
Post-Zygotic
Barriers
Reduced Hybrid Viability
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Genes of the different parent species may interact
and impair the hybrid’s development
Hybrids are very weak and/or underdeveloped
Salamander
hybrid shows
incomplete
development
Reduced Hybrid Fertility
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Even if hybrids may live and be strong, they
may be sterile
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
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