Transcript Hardy-Weinberg Equation

Hardy-Weinberg Equation
Sometimes, it’s fairly easy to
determine if you have a genetic
disorder – the symptoms can be very
obvious. However, just because you
don’t have a particular genetic
disorder doesn’t mean you don’t
carry it. People go to genetics
counselors who collect information
about your family history and build a
pedigree. From these pedigrees and
using a mathematical equation, they
can determine the chance that you
are a carrier.
Hardy-Weinberg Equation
1.
2.
Definition – An equation used to figure out how
common the carriers are based on knowing how
often a trait is inherited.
Frequency – How often something occurs;
usually written as a decimal.
25
Ex. 1 out of 4 people have blue eyes = ______%
0.25
As a decimal = ___________
Hardy-Weinberg Equation
D = dominant
r = recessive
All the genes present in a population of people:
frequency of dominant genes + frequency of recessive genes = 100%
OR
D+r=1
Ex. 75% of people have brown eyes
while 25% have blue eyes
0.75 + 0.25 = 1
Hardy-Weinberg
If two hybrid parents are crossed:
frequency of purebred Dom. ind. =
frequency of hybrid ind.= D*r +D*r OR
frequency of purebred rec. ind.= r2
D2 + 2Dr + r2 = 1
CARRIERS
D
r
D
DD
Dr
r
Dr
rr
D2
2D*r
HAVE RECESSIVE TRAIT
Hardy-Weinberg
If two hybrid parents are crossed:
D2 + 2Dr + r2 = 1
Hardy-Weinberg equations:
1. D + r
=
D
r
D
DD
Dr
r
Dr
rr
1
2. Have recessive trait = r2
3. Carriers = 2Dr
Sample problem
If tongue rolling (T) is dominant to non-tongue rolling (t), and 36% of the
population are non-rollers how common are the carriers of the nontongue rolling gene?
STEP 1: # of tt = 36%
OR
0.36
STEP 2: solve for number of t genes = t2 = 0.36
t = 0.6
STEP 3: solve for number of T genes = T + 0.6 = 1 T = 0.4
STEP 4: solve for carriers = 2T*t = 2(0.4)(0.6) = 0.48 or 48% of
pop. are carriers
PTC Taster
4 in 25 students are non-tasters
STEP 1: # of tt =
4/25 or 16% or 0.16
STEP 2:solve for number of t genes = t2 = 0.16
t = 0.4
STEP 3: solve for number of T genes = T + 0.4 = 1
T =0.6
STEP 4: solve for carriers = 2T*t = 2(0.6)(0.4) =
0.48 or 48% of pop. are carriers
Cystic Fibrosis
1 in 2500 babies (Caucasians)
STEP 1: # of cc = 1/2500 = 0.04% or 0.0004
STEP 2:solve for number of c genes = c2 = 0.0004 c = 0.02
STEP 3: solve for number of C genes = C + 0.02 = 1 C = 0.98
STEP 4: solve for carriers = 2C*c = 2(0.98)(0.02) =
0.039 or 3.9% of pop. are carriers
(approx. 1 in every 25 people)
Cystic Fibrosis
1 in 16,000 babies (AfricanAmerican)
STEP 1: # of cc = 1/16,000 or 0.00625% or 0.0000625
STEP 2:solve for number of c genes = c2 = 0.0000625
c = 0.008
STEP 3: solve for number of C genes = C + 0.008 = 1 C = 0.992
STEP 4: solve for carriers = 2C*c = 2(0.992)(0.008) =
0.015 or 1.5% of pop. are carriers
(approx. 1-2 in every 100 people)
Sickle Cell Anemia
9% of population in Africa
STEP 1: # of ss = 9% or 0.09
STEP 2:solve for number of s genes = s2 = 0.09
STEP 3: solve for number of S genes = S + 0.3 = 1
STEP 4: solve for carriers = 2S*s = 2(0.7)(0.3) =
0.42 or 42% of pop. are carriers
(almost half)
s = 0.3
S = 0.7
Genetic Disorder Project
Assignment #4
Use the Hardy Weinberg equation to determine the
frequency of carriers for your assigned genetic disorder.
STEP 1: # of ss =
STEP 2:solve for number of s genes =
STEP 3: solve for number of S genes =
STEP 4: solve for carriers =