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tee tee
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Posts: 63
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13 years ago
I have done some of each question. But i am having trouble. Thank you in advance and will donate at the end.

Question 1.                               
White Leghorn chickens are homozygous for a dominant allele, C, of a gene responsible for coloured feathers, and also for a dominant allele I, of an independently segregating gene that prevents the expression of C. The White Wyandotte breed of chickens is homozygous recessive for both genes, c/c,i/i. What proportion of the F2 progeny obtained from mating White Leghorn X White Wyandotte F1 hybrids would be expected to have coloured feathers

Question 2.
 Seborrheic keratosis is a rare hereditary skin condition due to an autosomal dominant mutation. Affected people have skin marked with numerous small sharply margined, yellowish or brownish areas covered with a thin greasy scale. A man with keratosis marries a normal woman and they have three children.

a.   What is the chance that all three are normal?

b.   What is the chance that all three are affected?

Question 3.                                  
In D. virilise, the mutations dusky body (dy), cut wings (ct) and white eyes (w) are all recessive alleles located on at different places on the x chromosome. Females heterozygous for all three mutations were crossed to dy ct w males, and the following phenotypes were obtained

Class         Phenotype                  Number
1         wild type.                       18
2         dusky                        153
3         cut                            6
4         white                            76
5         cut, white                       150
6         dusky, cut                         72
7         dusky, cut, white                    22
8         dusky, white                     3
                           

(i)   What are the genotypes of the two maternal X chromosomes?
(ii)   What is the map order of the genes on the X chromosome?
(iii)   What are the two-factor recombination frequencies between each pair of genes?
(iv)   Are there as many observed double-crossover gametes as you would expect if there was no interference?
(v)   What is the coefficient of coincidence and interference in this region?

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Bio_World100Bio_World100
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13 years ago Edited: 13 years ago, Bio_World100
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wrote...
On Hiatus
13 years ago
Sorry.  I made a mathematical error:

(3/4)(1/4) is NOT 1/16.  It's 3/16. Smiling Face with Open Mouth 

wrote...
On Hiatus
13 years ago Edited: 13 years ago, Bio_World100
The best way to approach the 2nd question is by way of drawing a pedigree.  Well...I don't think one is really needed for this question since there are ONLY two generations.  

Question 2

So, let's define our alleles:

A = dominant (seborrheic keratosis)
a = recessive (normal)

So, there can be either one of two crosses:

Aa (man) x aa (woman)    or    AA (man) x aa (woman)  

We know that a man has the disease, so he must have one of the following genotypes: Aa or AA.  Were not sure which one because the question doesn't specify whether he's heterozygous or homozygous.  So, the man's genotype would then be A_.  The _ could either be the "A" allele or the "a" allele.  The woman's genotype would have to be aa since she is normal.        

If the man's genotype were to be Aa, the children would either have the genotypes Aa or aa.  So, 1/2 normal and 1/2 carriers.  

If the man's genotype were to be AA, then ALL the children would have the genotype Aa and would all be carriers.  

a) The man could either be AA or Aa, so 1/2.  Since this question is asking for the probability that all three children will be normal, you would only have to consider the genotype Aa, since the "a" allele is normal.  So, the probability that all three children would be normal would be (1/2)^3 = 1/8

b) The answer to this question would be the same as question 2a.  This is because the question is asking for the chance that all three children would be affected, and therefore you would have to again consider AA or Aa, so 1/2.  For a child to be affected, he can either have the genotypes AA or Aa, so the answer should be 1/8.  

I know this is a little confusing, but if you still have any problems understanding this question, please feel free to send me a personal message and I will be more than willing to explain it to you.  

Hope this helps!  Smiling Face with Open Mouth

I will post the 3rd question next.
wrote...
Staff Member
13 years ago
Bio_World100 - awesome. Had no idea how to approach this lol Tee, please mark as solved.
- Master of Science in Biology
- Bachelor of Science
tee Author
wrote...
Donated
13 years ago

I will post the 3rd question next.

Thank you heaps, Just need help with the last question (3) but ill make my donation now.
Thank you once again for explaining it.
wrote...
Staff Member
13 years ago
Try to use this as reference and see if you can obtain the correct answer Thinking Face
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pokru,  biol1903,  Kcihczay,  N@t
- Master of Science in Biology
- Bachelor of Science
wrote...
13 years ago
Tanks for your help
i am working hard on the 3nd question
tee Author
wrote...
Donated
13 years ago
Tanks for your help
i am working hard on the 3nd question

do you get question 3, i just cant wrap my head around it.
tee Author
wrote...
Donated
13 years ago
i am going to  try and attempt it again today coz its due at the end of the day. if i get it ill post the answer.

But if so can someone please help me asap!!!  Face with Rolling Eyes
wrote...
Valued Member
13 years ago
i am going to  try and attempt it again today coz its due at the end of the day. if i get it ill post the answer.

But if so can someone please help me asap!!!  Face with Rolling Eyes

I'd like to see the solution if you're done, I hate genetics.
tee Author
wrote...
Donated
13 years ago
Try to use this as reference and see if you can obtain the correct answer Thinking Face

I will post the 3rd question next.
[/quote]

Can u tell me if this is right:

Question 3.                                 
In D. virilise, the mutations dusky body (dy), cut wings (ct) and white eyes (w) are all recessive alleles located on at different places on the x chromosome. Females heterozygous for all three mutations were crossed to dy ct w males, and the following phenotypes were obtained

Class         Phenotype                  Number
1         wild type.                            18
2         dusky                                  153
3         cut                                      6
4         white                                 76
5         cut, white                         150
6         dusky, cut                            72
7         dusky, cut, white               22
8         dusky, white                     3
                           

(i)   What are the genotypes of the two maternal X chromosomes?
(ii)   What is the map order of the genes on the X chromosome?
(iii)   What are the two-factor recombination frequencies between each pair of genes?
(iv)   Are there as many observed double-crossover gametes as you would expect if there was no interference?
(v)   What is the coefficient of coincidence and interference in this region?
Answers question tree someone please tell me if I’m on the right track

a) Parents
Dy Ct W  / dy ct w  X    dy ct w/  dy ct w   

b)
Class         Phenotype                  Number
1         dusky                                  153                         Parental no cross over’s
2         cut, white                           150

3         white                                   76                        Recombinants Single cross over Region 1
4         dusky, cut                            72

5         dusky, cut, white               22                        Recombinants Single cross over Region 2
6         wild type.                            18

7         cut                                      6                           Recombinants double cross over
8         dusky, white                          3

Cross over in region 1 dy-ct
76+72+6+3 /500 x 100
= 31.4%
Cross over in region 2 ct-w
22+18+6+3/500 x 100
= 9.8%
Gene map
dy------------------------------ct-------------w
|--------------------------------|--------------|
            31.4%                    9.8%
|-----------------------------------------------|
                     41.2%
I don’t know the rest of the answers its due in 3 hrs.



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