Have no clue....Genetics

[littleduce]

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I guess I just really suck at genetics but how would you go about this Q'?

Predict the phenotypes and their ratios for the cross Ggss x ggSs?

tell me if what I'm doing is wrong. On my practice exams I would cross Gg x gg then ss x Ss. get the ratio and multiply them together. then answer but it seems that you cant do that on this problem.

Here is another Q'. Lets say they wanted the probability of ggSs? how would you find that?

or what if they give you just find the probability of different genotypes of AaBBCc?

I have gone over all the genetics in KB DAT book, KB MCAT book, online, but just cant seem to understand how it all works.

Do you guys have an easier way to explain this or any short cuts to get the answer? Plz help!!! Thank you guys

 

[sbdento]

You have to look at which alleles each parent will pass on. Each parent will only pass on one allele from each gene. Since we are looking at two genes parent one will pass on Gs and gs and parent two will pass on gS and gs. Do the punnent square with those options and you will get 4 different results. You should be able to find all of your probabilities from that.

If there are three or more genes just use the same method, but make sure you are looking at what each parent can possibly give. Or which packet of alleles they can donate to the offspring. They give a packet of one allele per gene represented in the example.

 

[UCB05]

I guess I just really suck at genetics but how would you go about this Q'?

Predict the phenotypes and their ratios for the cross Ggss x ggSs?

tell me if what I'm doing is wrong. On my practice exams I would cross Gg x gg then ss x Ss. get the ratio and multiply them together. then answer but it seems that you cant do that on this problem.

Here is another Q'. Lets say they wanted the probability of ggSs? how would you find that?

or what if they give you just find the probability of different genotypes of AaBBCc?

I have gone over all the genetics in KB DAT book, KB MCAT book, online, but just cant seem to understand how it all works.

Do you guys have an easier way to explain this or any short cuts to get the answer? Plz help!!! Thank you guys

Keeping in mind the law of independent assortment, you can treat the probabilities of the two genes separately, and multiply those together. if you have Ggss x ggSs, the breakdown minipunnet frequencies are:

Gg x gg = .50 Gg, .50 gg
ss x Ss = .50 Ss, .50 ss

the probability of the two genes assorting to diploid offspring are:
Gg & Ss = (.50)(.50) = .25
Gg & ss = (.50)(.50) = .25
gg & Ss = (.50)(.50) = .25
gg & ss = (.50)(.50) = .25

You can do a 4-unit punnett, but it will get you the same answer:
GgSs = 4/16
Ggss = 4/16
ggSs = 4/16
ggss = 4/16

Same concept goes for figuring out haploid genotype frequencies. If you have AaBBCc, you get:
.5 frequency A, .5 frequency a
1.0 frequency B
.5 frequency C, .5 frequency c

so your chances for different genotypes are the product of the 3 genes frequencies you're interested in.

Also keep in mind genotype =/= phenotype.