Genetics

1
Hardy-Weinberg Equation

• Sometimes, its fairly easy to determine if you
  have a genetic disorder the symptoms can be
  very obvious. However, just because you dont
  have a particular genetic disorder doesnt mean
  you dont 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.

2
Hardy-Weinberg Equation

• 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 ___________
3
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
Ex. 75 of people have brown eyes while 25 have
blue eyes
D r 1
0.75 0.25 1
4
Hardy-Weinberg

• If two hybrid parents are crossed
•  

D r
D DD Dr
r Dr rr
frequency of purebred Dom. ind. D2
frequency of hybrid ind. Dr Dr OR 2Dr
DD
Dr
frequency of purebred rec. ind. r2
Dr
rr
D2
2Dr
r2
1
5
Hardy-Weinberg

• If two hybrid parents are crossed
•  

D r
D DD Dr
r Dr rr
D2 2Dr r2 1
Hardy-Weinberg equations
D r 1
1.
2.
Have recessive trait r2
Carriers 2Dr
3.
6
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
  non-tongue rolling gene?
• STEP 1 of tt
• STEP 2 solve for number of t genes
• STEP 3 solve for number of T genes
• STEP 4 solve for carriers

36 OR 0.36
0.6
t2 0.36 t
T 0.6 1 T
0.4
2Tt 2(0.4)(0.6)
0.48 or 48 of pop. are carriers
7
PTC Taster
4 in 25 students are non-tasters
STEP 1 of tt STEP 2solve for number of t
genes STEP 3 solve for number of T genes
STEP 4 solve for carriers
4/25 or 16 or 0.16
t2 0.16 t
0.4
T 0.4 1 T
0.6
2Tt 2(0.6)(0.4)
0.48 or 48 of pop. are carriers
8
Cystic Fibrosis
1 in 2500 babies (Caucasians)
STEP 1 of cc STEP 2solve for number of c
genes STEP 3 solve for number of C genes
STEP 4 solve for carriers
1/2500 0.04 or 0.0004
0.02
c2 0.0004 c
C 0.02 1 C
0.98
2Cc 2(0.98)(0.02)
0.039 or 3.9 of pop. are carriers (approx. 1
in every 25 people)
9
Cystic Fibrosis
1 in 16,000 babies (African-American)
STEP 1 of cc STEP 2solve for number of c
genes STEP 3 solve for number of C genes
STEP 4 solve for carriers
1/16,000 or 0.00625 or 0.0000625
c2 0.0000625 c
0.008
C 0.008 1 C
0.992
2Cc 2(0.992)(0.008)
0.015 or 1.5 of pop. are carriers (approx. 1-2
in every 100 people)
10
Sickle Cell Anemia
9 of population in Africa
STEP 1 of ss STEP 2solve for number of s
genes STEP 3 solve for number of S genes
STEP 4 solve for carriers
9 or 0.09
0.3
s2 0.09 s
S 0.3 1 S
0.7
2Ss 2(0.7)(0.3)
0.42 or 42 of pop. are carriers (almost half)
11
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 2solve for number of s
genes STEP 3 solve for number of S genes
STEP 4 solve for carriers