Blood Group Genetics - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

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


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 03-18-2013
USMLE Forums Scout
 
Steps History: Not yet
Posts: 10
Threads: 5
Thanked 2 Times in 2 Posts
Reputation: 12
Genetics Blood Group Genetics

A man with the blood type A and Rh+ marries a woman with A and Rh- blood-type. They have two boys who both have O- blood. Assuming simple Mendelian inheritance of blood type and Rh, what is the probability that their next two children will be male and will have O- blood, too?
A. 1/8
B. 1/16
C. 1/32
D. 1/64
E. 1/256
Reply With Quote Quick reply to this message



  #2  
Old 03-18-2013
USMLE Forums Guru
 
Steps History: Not yet
Posts: 375
Threads: 17
Thanked 131 Times in 81 Posts
Reputation: 147
Default

A. 1/8 ?????????
Reply With Quote Quick reply to this message
  #3  
Old 03-18-2013
USMLE Forums Scout
 
Steps History: Not yet
Posts: 10
Threads: 5
Thanked 2 Times in 2 Posts
Reputation: 12
Default

Anwer is C. I don't know how to get it though.
Reply With Quote Quick reply to this message
 
  #4  
Old 03-18-2013
tai35's Avatar
USMLE Forums Addict
 
Steps History: Not yet
Posts: 133
Threads: 25
Thanked 25 Times in 21 Posts
Reputation: 35
Question

Can someone please explain, what determines if the Kids get the O + or O - genotype ? I mean which one is dominant ? I thought the blood group is co dominant genetics
Reply With Quote Quick reply to this message
  #5  
Old 03-18-2013
USMLE Forums Veteran
 
Steps History: CS Only
Posts: 219
Threads: 44
Thanked 44 Times in 33 Posts
Reputation: 54
Default

Ive read about it online:
ABO system: A and B are dominant (3 alleles A,B and O)
So to be blood gp A, u can be AA or AO for example

Rh system: controlled by two genes: one is dominant and makes the person Rh+

The answer i came up with is 1/16 for their next kid to be male, O-
The question asks for the chance their "two" next kids to be O-. I thought that we multiply the chances of each kid, so 1/16 * 1/16.. But it doesn't give the answer..

That was my try .. Not sure if its correct
Reply With Quote Quick reply to this message
The above post was thanked by:
Easy (05-08-2013), Taayseer (08-23-2014)
  #6  
Old 03-18-2013
USMLE Forums Addict
 
Steps History: Not yet
Posts: 135
Threads: 3
Thanked 73 Times in 48 Posts
Reputation: 83
Default

E) 1/256, that's what i'm getting
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
You can't confuse the confused!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message
  #7  
Old 03-19-2013
MedicalExaminer's Avatar
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 824
Threads: 66
Thanked 463 Times in 298 Posts
Reputation: 473
Default

1/2 chance of having son x 1/4 chance of son being blood group O x 2/4 chance of being rh negative x by same data for another child = 4/1024=1/256
__________________
Everything is possible for him who believes (MARK 9:23)
245/247/passed on 1st attempt/223/2mos Obsie /3 US LORS/visa not needed/2008 grad
Reply With Quote Quick reply to this message
The above post was thanked by:
Ahmer Asif (07-30-2015)
  #8  
Old 03-19-2013
USMLE Forums Addict
 
Steps History: Not yet
Posts: 138
Threads: 1
Thanked 46 Times in 26 Posts
Reputation: 56
Default

yeah I'm getting 1/256 aswell
Reply With Quote Quick reply to this message
  #9  
Old 07-04-2016
USMLE Forums Scout
 
Steps History: Not yet
Posts: 40
Threads: 4
Thanked 1 Time in 1 Post
Reputation: 11
Default

P(male)=1/2
Quest says two male thus 1/2*1/2=1/4(independent)
P(blood group-O)=1/4(punnett)
P(rh negative)=1/2
Thus 1/2*1/4*1/4=1/32
Reply With Quote Quick reply to this message



Reply

Tags
Genetics-, Step-1-Questions

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
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.

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.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Skype group for CS Prep nikhilt USMLE Step 2 CS Study Partners 7 09-10-2015 06:35 PM
Handa Medical Group tramps USCE & Clinical Rotations 0 03-18-2013 09:44 AM
study group? fshyang USMLE Step 1 Forum 0 02-22-2012 09:35 AM
Study Group ideas DrRomy USMLE Step 1 Forum 15 12-14-2010 05:09 AM
Blood Brain Blood CSF Barriers Difference Sabio USMLE Step 1 Bits & Pieces 0 09-25-2009 08:23 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)