Alleles,Genotypes and Phenotypes

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    • #193
      Renee
      Participant

      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.

    • #18634
      biostudent84
      Participant

      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!

    • #18637
      Renee
      Participant

      Thank you so much. You are a life saver!

    • #18665
      Chris
      Participant

      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).

    • #18669
      biostudent84
      Participant

      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).

    • #19094
      2810712
      Participant

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

    • #19128
      Poison
      Participant
      quote biostudent84:

      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.)

    • #19156
      2810712
      Participant

      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 ……………

      hrushikesh

    • #19158
      biostudent84
      Participant

      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)

    • #19160
      Poison
      Participant
      quote 2810713:

      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.

    • #19161
      biostudent84
      Participant
      quote Poison:

      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.

    • #19169
      bizzaroSquirrel
      Participant
      quote 2810713:

      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 😉

    • #19171
      Poison
      Participant

      to your concerns…

      One well known example of mutation is non-disjunction. Non-disjunction is when the spindle fibres fail to seperate during meiosis, resulting in gametes with one extra chromosome and other gametes lacking a chromosome.

      If this non-disjunction occurs in chromosome 21 of a human egg cell, a condition called Down’s syndrome occurs. This is because their cells possess 47 chromosomes as opposed to the normal chromosome compliment in humans of 46.’

      here is the link:
      http://www.biology-online.org/2/7_mutations.htm

    • #19620
      2810712
      Participant

      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.
      I am explaining my q. here-
      There may be two or more forms of a gene i.e. two or more different DNA sequences
      . So, mutation may occur in any one of them . Let A & B be two diff. DNA sequences of a gene . If mutation occurs in A as well as in B , the two mutations are different in the sense they have different raw materials. so, we can’t simply group them under ” the mutations in the gene of some trait ” Thus the ” the mutations in the gene of some trait ”
      can be classified on the basis of raw materials [ the forms of a gene in which they have occured ] , so, the forms of genes are mutated . & what will you call the different forms of a gene i.e. different DNA sequences ? As per I know they R nothing but alleles !!!!
      Alleles are not phenotypes .

      hrushikesh

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