gatorPredent

10+ Year Member
Nov 9, 2008
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Florida
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Pre-Dental
Usually genetics questions are straight forward but lately iv gotten a few wrong. How Should i approach these?

1. How many genetically different gametes can be formed by a mouse that is genotypically AABbCc? (Assume no linkage)? answer is 4

2. In watermelons, the unlinked genes for green color (G) and for short length (S) are dominant over alleles for striped color (g) and long length (s). Predict the phenotypes and their ratios for the cross Ggss x ggSs. answer is 1:1:1:1

Thanks guys
 
Jun 14, 2009
800
3
Status
Pre-Dental
Usually genetics questions are straight forward but lately iv gotten a few wrong. How Should i approach these?

1. How many genetically different gametes can be formed by a mouse that is genotypically AABbCc? (Assume no linkage)? answer is 4

2. In watermelons, the unlinked genes for green color (G) and for short length (S) are dominant over alleles for striped color (g) and long length (s). Predict the phenotypes and their ratios for the cross Ggss x ggSs. answer is 1:1:1:1

Thanks guys
1. There's only one way to segregate A-A, two ways for B-b, two for C-c. Assuming no linkage as noted, the number of different genotypes for gametes would be 1x2x2.

2. start off by looking at the two genes separately. Gg x gg will only give you Gg and gg progeny in a 1:1 ratio. ss x Ss will only give Ss and ss progeny in a 1:1 ratio. Cross those and you get Ggss, GgSs, ggSs, ggss, all in equal probability. This is a problem where the genotypes each correlate with a different phenotype so it comes out to a 1:1:1:1 ratio. If there were two genotypes that result in the same phenotype, you'd add their ratio value together.
If for example a different question had a genotype result that included, GgSs and GGSS, you'd take the sum of their frequencies as a total ratio (1+1 = 2)
 

dentrilla

10+ Year Member
Aug 15, 2008
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Dental Student
Yup, 2nd question is a heterozygous test cross, might be important to know that. A test cross is when you cross with homozygous recessive in order to determine whether the other parent is homo or hetero dominant for the trait of interest. You determine this by looking at the characteristic pattern in the offspring.
 

Nasem

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Aug 30, 2006
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Lansing, MI
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Pre-Medical
Usually genetics questions are straight forward but lately iv gotten a few wrong. How Should i approach these?

1. How many genetically different gametes can be formed by a mouse that is genotypically AABbCc? (Assume no linkage)? answer is 4

2. In watermelons, the unlinked genes for green color (G) and for short length (S) are dominant over alleles for striped color (g) and long length (s). Predict the phenotypes and their ratios for the cross Ggss x ggSs. answer is 1:1:1:1

Thanks guys
1) for this one, just remember that when your talking about gametes, your talking about meiosis, meaning the end result will have only 1 copy of each gene..... for this problem, you have 3 genes:
first gene is AA
2nd gene is Bb
3rd gene is Cc
and they are all contained in a single cell, so your options are...
- So for the first gene, there is only one... and thats A (your done here)
- for the second gene, they can separate into B and b
- for the 3rd gene, they can separate into C and c

Just add the suckers up and ur all done
A+B+C
A+b+C
A+B+c
A+b+c


2) the parental cross is Ggss x ggSs
lets say P1 is Ggss
and P2 is ggSs

P1 gives the following gametes: Gs and gs
P2 gives the following gametes: gS and gs

lets see If I can draw the punnett square here lol
___ Gs | gs
gS GgSs | ggSs
___
gs Ggss | ggss

I think it came out right...