Mendelian Genetics

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

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sez123
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Mendelian Genetics

Post by sez123 » Mon Feb 09, 2009 12:20 am

The ability to taste the chemical PTC is an autosomal dominant phenotype, and the inability to taste is recessive. If a taster woman with a non taster father marries a taster man, who is a previous marriage had a nontaster daughter, what is the probability that their first child will be
i) a non taster girl
ii) a taster girl
iii) a taster boy

What is the probability that their first two children will be tasters of any sex?

OK so i have made an attempt at this. From what i have done, i think the taster man must be heterozygous, since he produced a non taster daughter from his previous marriage.

but now i am thinking all this information is insignificant, just to complicate things. Should i just start with the taster mother (displays dominant phenotype) and non taster father(displays recessive phenotype)?

hmm now i have confused myself further! any help greatly appreciated thanks!

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mith
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Post by mith » Mon Feb 09, 2009 2:49 am

No, it is necessary info. You're right that the father has to be hetero to be both a taster and a non-taster parent.

Using the same line of reasoning, you can figure out who the mother must be and then, it's downhill from there.
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Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
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GeGnome
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Re: Mendelian Genetics

Post by GeGnome » Thu Feb 12, 2009 8:14 am

sez123 wrote:The ability to taste the chemical PTC is an autosomal dominant phenotype, and the inability to taste is recessive. If a taster woman with a non taster father marries a taster man, who is a previous marriage had a nontaster daughter, what is the probability that their first child will be
i) a non taster girl
ii) a taster girl
iii) a taster boy

What is the probability that their first two children will be tasters of any sex?

OK so i have made an attempt at this. From what i have done, i think the taster man must be heterozygous, since he produced a non taster daughter from his previous marriage.

but now i am thinking all this information is insignificant, just to complicate things. Should i just start with the taster mother (displays dominant phenotype) and non taster father(displays recessive phenotype)?

hmm now i have confused myself further! any help greatly appreciated thanks!


It's pretty obvious that the woman is heterozygous with the information provided considering it states she's a taster with a nontaster father.

The father is a taster, but had a nontaster daughter. Assuming his previous wife was faithful to him, he must also be heterozygous.

T = dominant for taster, t = recessive.
The mother is Tt.
The father is Tt

Do the punnet square and then figure out the phenotypic ratios. A phenotype is an expressed characteristic, so you only care about the traits that reveal themselves.

To answer the first question, what is the probability of having a child with the nontaster phenotype? Multiply that with the probability of having a female. The probability of having a female is 1/2, and the probability of having a male is also 1/2.

The rest should be obvious.

miloshic
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Post by miloshic » Thu Feb 12, 2009 9:38 am

Tt x Tt
and you get TT Tt Tt tt
1. 3/4*1/2=3/8
2. 1/4*1/2=1/8
3. 3/4*1/2=3/8
I think I did this well :)

GeGnome
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Re:

Post by GeGnome » Thu Feb 12, 2009 3:34 pm

miloshic wrote:Tt x Tt
and you get TT Tt Tt tt
1. 3/4*1/2=3/8
2. 1/4*1/2=1/8
3. 3/4*1/2=3/8
I think I did this well :)


You only got one of the answers correct.

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