General Interview Questions - Alleles, mutations & phenotypes

What is the difference between an allele and a mutation? How is an allele different from a gene?

Explain in terms of gene product function how a mutant allele can be dominant? recessive?
Describe how the genotype of an organism can influence the phenotype associated with a particular allele.

What does it mean to say that an allele is pleiotropic?
What does it mean to say that an allele of one gene is epistatic to that of another?

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1. Genes can exist in different versions, which differ in the nucleotide sequence; these versions are known as alleles.
2. The complete set of genes carried by an organism is its genome; the specific set of alleles it carries is known as its genotype.
3. The specific features of an organism is known as its phenotype.
4. The phenotype is a function of the genotype and environmental and molecular events that occur during embryonic development and thereafter.
5. Some phenotypic traits are due to the allelic composition of a single gene, most are based on a large number of different genes.
6. During meiosis the process of recombination can lead to the formation of new alleles and new combinations of alleles along a chromosome.
7. The process of sexual reproduction can generate vast numbers of possible genotypes.
8. All alleles have their origins as a mutation or a recombination event.  The original version of the gene, before the mutation, is known as the wild type allele.
9. A specific gene is also known as a genetic locus (position).   In a particular population of organisms, the number and frequency of alleles of a specific genetic locus will be determined by various factors, including founder effects, genetic drift and natural selection.  Generally the most frequent allele will be considered the wild type, but this is an artificial convention.
10.  Genes produce products, either RNAs or (indirectly) polypeptides (proteins).  
11. A mutation can alter either the gene product itself, its regulation (when, where and how much is produced). 
12. We can classify mutations formally, without even knowing what the gene products do or how the mutation alters them in the following terms.  A mutation can be amorphic (no gene product produced), hypomorphic (the gene product has the same function, but is less active than the wild type), hypermorphic (the gene product has the same function, but is more active than the wild type), antimorphic (the mutant gene product antagonizes the function of the wild type product) or neomorphic (the gene product has a new function, different from the wild type gene produce).   
13. Haploid organisms have a single copy of each genetic locus.  Diploid organisms have two copies (one inherited from the maternal parent the other from the paternal parent).  In a diploid organism, if a phenotypic trait is determined by one allele, irrespective of the nature of the other allele at the genetic locus, the determining allele is said to be dominant, the other allele(s), recessive.
14 Most alleles are neither strictly dominant or recessive, but interact in complex ways with each other and the rest of the genotype to determine phenotype.   

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