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Alleles,Genotypes and Phenotypes

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Alleles,Genotypes and Phenotypes

Postby Renee » Wed Nov 10, 2004 4:23 am

Can someone help me answer these two questions 1. What is one way that new alleles can be produced on a certain gene? 2. How can mutations affect genotypes and phenotypes? Please Help me! I wiould greatly appreciate any input into these two questions.
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Postby biostudent84 » Fri Nov 12, 2004 3:17 am

Sure thing!

An allele is a pair of genes, in which the more dominant of the two is expressed. My parents' alleles for hair are (dad) Brown/Blonde, (mom) Blonde/Red. Take one (random) half an allele from mom, and another (random) half from dad. My sister, who has blonde hair, recieved the blonde/blonde allele. The expressed gene is blonde. I, on the other hand, have brown hair. My expressed gene, the stronger of the two is brown. The other half of my allele can either be red or blonde. This other half of my allele is the weaker of the two, and will only be expressed if it becomes the dominant gene in my offspring.

Mutations are literally mistakes in the replication of DNA. When this occurs in the gametes (sex cells), they are passed onto the alleles of offspring. When this mutation is the weaker of the two genes recieved, it becomes a recessive gene. 99% of the time, a mutation that becomes expressed will result in a miscarraige...but sometimes, it will be non-fatal and be expressed. This can result in some diseases. Albinism, Sickle-cell Anemia, and additional digits comes to mind.

I hope this helps!
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Postby Renee » Sat Nov 13, 2004 5:29 am

Thank you so much. You are a life saver!
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Postby Chris » Wed Nov 24, 2004 2:23 am

I believe that down syndrome is the most common non-fatal example of this. It is an example of trisomy (having 3 chromosomes of one kind other than 2).
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Postby biostudent84 » Tue Nov 30, 2004 6:30 pm

Down's Syndrome is not the result of a mutation. It is the result of the chromosomes in an older mother failing to completely couple with the chromosomes of the father. The result is an additional Chromosome #22...causing slight tilting of the eyes, oversized tounge, mental retardation, and other effects. It only happens in older women having children (older men are not at risk of producing down babies).
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Postby 2810712 » Sat Jan 22, 2005 5:19 am

allele is mutated or the gene? I think, it's the allele- because one gene may have many alleles .What is ur opinion?
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Postby Poison » Sun Jan 23, 2005 9:33 am

biostudent84 wrote:Down's Syndrome is not the result of a mutation. It is the result of the chromosomes in an older mother failing to completely couple with the chromosomes of the father. The result is an additional Chromosome #22...causing slight tilting of the eyes, oversized tounge, mental retardation, and other effects. It only happens in older women having children (older men are not at risk of producing down babies).


There are a few things that results in down's syndrome.
And there are 3 types of mutations. 1) structural changes on chromosomes 2) changes on the number of the chromosomes 3) point mutations
So why do you say that Down's Syndrome is not a result of mutation?
As much as I know 21. chromosome trisomy (2n+1) also causes Down's Syndrome. (you know trisomy is the numerical change of chromosomes.)
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please help...

Postby 2810712 » Wed Jan 26, 2005 1:08 pm

Is trisomy a type of mutation ? How wud U classify it ? As per I remember the cases of mutations due to change in number of chromosomes [?] [or change in the no. of gene/s] include the appearance of more or less copies than normal ,of one or more genes. Can we say that this is same as
trisomy? Trisomy is a result of non-disjunction and mutations are due to some radiations or chemicals or other such things , as per I know . So , think this is not muation. PLEASE HELP IF I AM WRONG ...............

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Postby biostudent84 » Wed Jan 26, 2005 5:09 pm

As individuals get older, chromosome recombinations do not work well. Trisomy ini chromosome pair 21 is the result of the female's chromosomes not binding to the male's properly due to the female's age (a man can be as old as he wants to and it will not affect the occurence of Down's Syndrome)
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Re: please help...

Postby Poison » Wed Jan 26, 2005 7:14 pm

2810713 wrote: Trisomy is a result of non-disjunction and mutations are due to some radiations or chemicals or other such things , as per I know . So , think this is not muation.

hrushikesh


mutations are sudden and permenant changes in DNA. according to you, we must say that thalassemia is also a cause of chemical or radiation. (as you say all mutations are due to radiation or chemicals). Is it true? I dont think so.
and about trisomy: as much as I know changing in number of chromosomes is also a mutation. I had an exam few weeks ago. there was a question like that which I got full mark.
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Re: please help...

Postby biostudent84 » Wed Jan 26, 2005 8:16 pm

Poison wrote:much as I know changing in number of chromosomes is also a mutation. I had an exam few weeks ago. there was a question like that which I got full mark.


Teachers can be wrong just as much as anyone else. While it is rare, it is possible. Trisomy resulting from failure of chromosomes to properly combine is technically not mutation.

Definition is a CHANGE in the structure or sequence of DNA. In order for DNA to change, you must have a previous version of DNA to go by. Whenever fertilization occurs, two half-sets of chromosomes (I.E. DNA) combine to make a whole genome. There is no existing "original" DNA structure in which a trisomy can occur.

Ok, that sounds complicated. Let me make an example.

I have two bikes, both similar, but not identical. The idea is for me to tear these bikes apart to make a new, supposedly better bike from parts of the original two. I intend to make another similar two-wheel bike, but end up making a tricycle. While this new creation is different from the parent deisgns, the new design did not "mutate" as there is no preexisting structure in which it had.

Mutations in this example would be if the bike rusted, warped, bent, etc.
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Postby bizzaroSquirrel » Thu Jan 27, 2005 9:36 am

2810713 wrote:allele is mutated or the gene? I think, it's the allele- because one gene may have many alleles .What is ur opinion?
hsg


The allele refers to the phenotype of the gene, or the trait that the gene codes for. Example, in mendels' little pea pod experiment, there were 2 genes, one for smooth seeds and one for wrinkled seeds. So there are 2 alleles here (and they are usually shown by a capital and normal letter, S for smooth, s for wrinkled).

Genes become mutated.

by the way this is my first post, so hi all :wink:
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