USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
 Home USMLE Articles USMLE News USMLE Polls USMLE Books USMLE Apps
 Register FAQs Members List Search Today's Posts Mark Forums Read

 USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

#1
06-24-2010
 USMLE Forums Veteran Steps History: 1 + CK Posts: 234 Threads: 63 Thanked 127 Times in 63 Posts Reputation: 157

pls I need help on how to apply hardy Weinberg equation. I don't understand how to use it to solve questions in genetics. pls i need explanation. my exam is quite near.
 The above post was thanked by: drzamzam (08-17-2015), Usmle16Forall (11-26-2016)

#2
06-27-2010
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 363 Threads: 18 Thanked 310 Times in 148 Posts Reputation: 320

Quote:
 Originally Posted by achistikbenny pls I need help on how to apply hardy Weinberg equation. I don't understand how to use it to solve questions in genetics. pls i need explanation. my exam is quite near.
what do you need help with? What the equation means? what the p^2+2pq+q^2=1 means?

I assume you know what Hetero, Homo is?
 The above post was thanked by: achistikbenny (06-28-2010), drzamzam (08-17-2015), Ronald (06-27-2010)
#3
06-28-2010
 USMLE Forums Veteran Steps History: 1 + CK Posts: 234 Threads: 63 Thanked 127 Times in 63 Posts Reputation: 157

thanks, i know what homozygous and hetero means but i dont know how to apply it using HW equation. i will really appreciate if u can help me here.
#4
06-28-2010
 USMLE Forums Guru Steps History: 1+CK+CS+3 Posts: 363 Threads: 18 Thanked 310 Times in 148 Posts Reputation: 320

Quote:
 Originally Posted by achistikbenny thanks, i know what homozygous and hetero means but i dont know how to apply it using HW equation. i will really appreciate if u can help me here.
Ok, sorry if this is going to be a long post.

^2 = to the power of 2

Equation:
(p+q=1)^2 or p^2 +2pq+q^2=1

AA=p^2
Aa=2pq
aa=q^2

The best way to learn how to use the equation is by following examples.

Autosomal Dominant Inheritance
-------------------------------
Achondroplasia Dwarfism (AD Lethal)- Study of Achondroplasia documented 7 new cases out of 250 000 in the USA. IN achondroplasia Homoqygensity is genetic lethat.
What is the Allele Frequency of Acondroplasia in the USA population?

Solution-
-7/250 000 = .000028

-Aa = 2pq
2pq=.000028

Allele Frequency p of the disease is small in AD
allele frequency q is ~1 in AD

so since q is about 1, then really the 2pq can just become 2p.

2p=.000028 / 2 (divide 2p and the .00028 by 2)
p=.00614 or 1/71428

Huntingtons occurs in the USA at a frequency of 1/10000 or .0001.
Huntingtons is homoqygosity is not genetic lethal.
What is the allele frequency of homo dominant (HD) gene in the USA

solution
P^2+2pq+q^2=1

All geno's containing HD include: AA=p^2 and Aa=2pq

Thus frequency is equal to p^2+2pq=.0001

Frequency of homo (p^2) is small ~0
allele frequency q is about 1, so

2p(1) or 2(p) = .0001

2p/2 = .0001/2
p=.00005 or 1/20 000

I assume that AD diseases q is 1 all the time so just figure out p

Autosomal Recessive (q^2 is equal to the disease frequency)
----------------------
Autosomal recessive disorders homogenciity aa produces the disorder.
ex- homo (dd) for sickle cell produces the disorder where as Hetero (Dd) is a carrier.

Sickle Cell
A study of sickle documented 10 new cases out of 6 250 in the AA population.

-what is the allele frequency (p) of the sickle gene in AA population?
- What is the frequency of the hetero carrier?

Solution
- Frequency= 10/6 250 = 1/625 or .0016

2- SS gene showing disease is homo aa=q^2

disease show is q^2=.0016
take square root of q^2 of .0015
q=.04 or 1/25

Allele frequency p of sickle is 1-q
p= 1.00-.04=.96
Allele frequency (p) of ss normal is .96 or 1/1.04

Frequncey of Hetero Carrier is 2pq
2(.96)(.04)=.0768 or 1/13

X-Link Dominant (q is equal to disease frequency)
-----------------
-Observed twice the # of females than of males. Males usually die

EX: rhetts syndrome
Study of Rhetts documented 10 new cases out of 180 000 over the last 10 years.

What is the Allele Frequency (q) of rhetts in the usa
what is the allele frequency (p) of rhetts in the usa

Solution
1- 10/180 000 = 1/18 000 or .00006

Allele frequency (q) is equal to the disease frequency. This means q=.00001 or 1/ 100 000

3- Allele frequency (p) of rhetts normal gene is 1-q
meaning p=1.00 - .00001 = .999 or ~1

Allele frequency )p_ of rhetts normal gene is .999 or 1/1.0001

X-Link Recessive (q is equal to the disease frequency)
----------------
X-link recessive is only observed in males
ex- hunters

Hunters
study in the usa documented 10 new cases out of 1 000 000 over 5 years.

What is the allele frequency (q) of hunters in the USA
what is the allele frequency (p) of hunters in the USA
what is the female Hetero carrier?

solution
1- 10/100 000 - 1/10 000 or .00001

2- x link recessive allele frequency (q) equals disease frequency
q=.00001

3- allele frequency (p) of hunters normal is 1-q
p=1.00-.00001 = .9999 or ~1
Allele frequency (p) of hunters normal gene is .9999

4- Frequency of female geterocarrier is 2pq
p=~1
2pq = 2(1) (.00001)
= .00002 or 1/50 000

I hope this helps some. The best thing you can do, is print this out and do other questions and use this as a guide. Out of a handful of people I've talked to, only maybe 1 has gotten a question on these types of quesitons

If you need an clarification, let me know. I type 2 quick sometimes and mispell or my piece of of **** 1 year old dell laptop keyboard doesn't work sometimes.

 The above post was thanked by: achistikbenny (06-29-2010), jugraj (08-08-2013), Karrar (07-03-2010), mazrodin (07-04-2010)
#5
06-29-2010
 USMLE Forums Veteran Steps History: 1 + CK Posts: 234 Threads: 63 Thanked 127 Times in 63 Posts Reputation: 157

thank u Peewee for making out time to type and explain all these for me i honestly appreciate . thank u very much.
#6
07-03-2010
 USMLE Forums Newbie Steps History: --- Posts: 1 Threads: 0 Thanked 1 Time in 1 Post Reputation: 11

[QUOTE=Peewee;11259]....hey!p2 is taken for homozygous....i.e:complete homozygous n dominant traits....n q2 for homogyous recessive...n 2pq for heterozygous individuals......if the frequency is given u can find out the total population....n if the population is given u can find out the frequency of the homozygous [dominant or recessive]and heterozygous populations.....hope now u can solve the problems....if u still hav doubt u can mail me a question to my gmail account....ill solve that n ll send u...all the best for u r exam.....bye...
 The above post was thanked by: achistikbenny (07-03-2010)
#7
07-03-2010
 USMLE Forums Veteran Steps History: 1 + CK Posts: 234 Threads: 63 Thanked 127 Times in 63 Posts Reputation: 157

thank u very much but u didnt leave ur gmail address.

 Tags Genetics-

Message:
Options

## Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
User Name:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
 AMG IMG ---
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

 Not yet Step 1 Only CK Only CS Only 1 + CK 1 + CS 1+CK+CS CK+CS 1+CK+CS+3 ---
Favorite USMLE Books
 What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
 Where you live. Leave blank if you don't want to tell.

## Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.