3 point test

Genetics as it applies to evolution, molecular biology, and medical aspects.

Moderators: honeev, Leonid, amiradm, BioTeam

Post Reply
jjfptl
Garter
Garter
Posts: 5
Joined: Mon Oct 22, 2007 6:29 pm

3 point test

Post by jjfptl » Sun Nov 18, 2007 8:44 am

Hi, I have this data:
A three point testcross was made in corn. The alleles C and c result in colored versus colorless seeds, Wx and wx in nonwaxy versus waxy seeds, and Sh and sh in plump versus shrunken seeds. When plants grown from seeds heterozygous for each of these pairs of alleles were testcrossed, the progeny were as follows.

colorless, nonwaxy, shrunken 84
colorless, nonwaxy, plump 974
colorless, waxy, shrunken 20
colorless, waxy, plump 2349
colored, waxy, shrunken 951
colored, waxy, plump 99
colored, nonwaxy, shrunken 2216
colored, nonwaxy, plump 15

and I need to find: a) the genotype of the heterozygous parent, b) the order of the three genes, c) the genetic distance between each gene and d) calculate interference

I have done the problem, just wondering if I am right.......
Genotype of heterozygous parent: cwxSh /CWxsh
Gene order: C Sh Wx
Distance: C-----→Sh = 29cM
Sh---→Wx = 3.2cM
Interference: 44%

my other question is, what is the easiest way to find the gene order in a problem like this? I have been searching tests, etc and I can't find a good answer. They start to explain a visual method, but they just kinda stop and assume you know what they are talking about. I looked at the parental genotypes and the double recombinant genotypes and the order I came up with seems to work, but I am really not sure.........thanks all!

User avatar
mith
Inland Taipan
Inland Taipan
Posts: 5345
Joined: Thu Jan 20, 2005 8:14 pm
Location: Nashville, TN
Contact:

Post by mith » Sun Nov 18, 2007 5:18 pm

The easiest way to find the gene order is to look at the most numerous phenotypes which constitute your two parents. Now the least numerous is the double crosses(middle gene switched). So example:

Most: AB+C / A+BC+
Least: A+B+C / ABC+

Gene order BAC or CAB
Living one day at a time;
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
~Niebuhr

jjfptl
Garter
Garter
Posts: 5
Joined: Mon Oct 22, 2007 6:29 pm

Post by jjfptl » Mon Nov 19, 2007 1:22 am

Well, I am still confused...not sure what exactly is switching. I know my parentals and double recombinants, and that lead me to the folowing gene order:
Parentals: cwxSh /CWxsh = Gene order: C Sh Wx
double recombinants: CWxSh/cwxsh
Also, when listing the gene order, do you list the dominants? Sorry, just feeling really lost and I am sure it is quite simple.....Are my answers correct?
Thanks

User avatar
mith
Inland Taipan
Inland Taipan
Posts: 5345
Joined: Thu Jan 20, 2005 8:14 pm
Location: Nashville, TN
Contact:

Post by mith » Mon Nov 19, 2007 3:35 am

Sorry, by switches I mean double recombinants.
Living one day at a time;
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
~Niebuhr

jjfptl
Garter
Garter
Posts: 5
Joined: Mon Oct 22, 2007 6:29 pm

Post by jjfptl » Mon Nov 19, 2007 7:35 am

sorry, I am still not following........thanks for trying though! I will try to figure it out on my own

Post Reply

Who is online

Users browsing this forum: No registered users and 5 guests