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?

Bellringer-March 23, 2015

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

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?

Problem #2

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

Evolution and Zygotic Barriers (Macroevolution

part 2)Ms. Kim

H. 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