Dihybrid Cross

View previous topic View next topic Go down

Dihybrid Cross

Post by Alla on Wed Mar 19, 2008 12:42 am

VPer wrote:I'm struggling with this problem:

A female fly with alleles S and C is mated with a wild-type male fly. F1 progeny is found to be 50% wild-type and 50% C (phenotypes). Draw the Punnet square for this cross.

I would also need help in determining the punnet square for the F2 progeny.

Given:
Female has alleles for C and S, and, therefore, presumed to display those phenotypes.
Male is wild type, and, therefore, presumed to be homozygous for WT alleles of
C and S phenotypes.
F1 progeny is 50% WT: 50% C phenotype

Without additional date, I would assume both mutations to be autosomal and unlinked.

1. Since male does not have alleles for C or S phenotype, F1 C phenotype progeny must be heterozygous and, therefore, mutant allele for C phenotype must be dominant.
2. Since mutant C allele is dominant but only 50% of F1 display this phenotype, Female F0 must have been heterozygous for C.
3. Since at least some of the F1 progeny have to be heterozygous for allele responsible for S phenotype but none of the F1 display S phenotype, mutation for it must be recessive.
4. Since mutation responsible for S phenotype is recessive, Female F0 must be homozygous for it (otherwise you would not be able to see S phenotype).

Let’s designate:
C – mutant allele of C phenotype
c – WT allele of C
S – WT allele of s
s – mutant allele of S phenotype

Your cross then is between female F0 Ccss and male F0 ccSS.
Expected F1 progeny would be 50% CcSs (C phenotype): 50% ccSs (WT phenotype)

For F2 progeny, unless otherwise instructed, I would cross two flies with
C phenotypes: CcSs x CcSs (gametes CS, Cs, cS, and cs). This cross will result in ratio of 9C: 3WT: 3CS: 1S phenotypes.

If you need more help, let me know.

I would appreciate it, if you registered to this site and used it directly.
Good luck!

Alla
Instructor
Instructor

Posts : 103
Join date : 2008-02-27

View user profile

Back to top Go down

Re: Dihybrid Cross

Post by VPer on Wed Mar 19, 2008 1:31 am

For the F2 progeny, it is instructed to "mate the F1 generation". Isn't that Ccss x ccSs?

How do you know which parents to pick to mate to get the F2 progeny?

Thank you for your help thus far.

VPer
Student
Student

Posts : 3
Join date : 2008-03-19

View user profile

Back to top Go down

Re: Dihybrid Cross

Post by Alla on Wed Mar 19, 2008 2:58 am

Your problem is a bit unusual. In most cases F1 generation is produced by breeding two homozygous parents different from each other (which is not the case here). Such cross would result in phonotypically homogenous heterozygous F1 population and mating F1 results in self-cross. In your problem that is not the case; so, like I said before, I would chose to mate two true heterozygous individuals (CcSs x CcSs) to get F2. However, I would suggest that you do Ccss x ccSs and ccSs x ccSs crosses as well (just to be on the safe side) or ask your teacher for clarification in this case ("mate the F1 generation" is not a clear instruction in the case with more than one F1 phenotype).

Alla
Instructor
Instructor

Posts : 103
Join date : 2008-02-27

View user profile

Back to top Go down

Re: Dihybrid Cross

Post by VPer on Wed Mar 19, 2008 3:35 am

I performed a cross using one with C phenotype and one with wild type (from F1). The results of the F2 progeny were 3WT:3C:1S:1SC.

How do I draw the Punnet square for this one?

VPer
Student
Student

Posts : 3
Join date : 2008-03-19

View user profile

Back to top Go down

Re: Dihybrid Cross

Post by VPer on Wed Mar 19, 2008 4:43 am

Nevermind, I got it.

The cross to determine the f2 generation is CcSs x ccSs.

Thank you for all of your valuable help!

VPer
Student
Student

Posts : 3
Join date : 2008-03-19

View user profile

Back to top Go down

Re: Dihybrid Cross

Post by Alla on Wed Mar 19, 2008 8:03 am

You are welcome!

Alla
Instructor
Instructor

Posts : 103
Join date : 2008-02-27

View user profile

Back to top Go down

Re: Dihybrid Cross

Post by Sponsored content


Sponsored content


Back to top Go down

View previous topic View next topic Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum