Tottaly confused...

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

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xllxashleexllx
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Tottaly confused...

Post by xllxashleexllx » Tue Apr 25, 2006 2:55 pm

Ok i have read the section in my bio book on Phenotypes Genotypes about 5 times. But i still dont under stand homozygous and heterozygous. Could anyone help me? Please?


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Ashlee

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Khaiy
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Post by Khaiy » Tue Apr 25, 2006 4:11 pm

Sure. A phenotype is just what trait is expressed in an organism. For example, I have brown hair, and so I display the brown hair phenotype.

Genotype is just the gene combination of an individual. Let's stick with hair for an example: My phenotype is brown, but that could be the result of different genotypes. Let's say that the allele for brown hair is dominant over the allele for blonde hair (So the brown hair allele is B, and the blonde hair allele is b). My brown hair phenotype could have come from having only brown hair alleles (genotype BB), or from having one brown allele and one blonde allele (Bb). But if I had blonde hair, then we would know that my genotype was bb.

Homozygous and heterozygous are descriptions of genotype. If I were homozygous for brown hair, then that means that both of the alleles I had would be the same (homo=same), and would code for brown hair. If I were heterozygous (heter=different), then that would mean that I had two different alleles, in this case the brown allele B and the blonde allele b. There is also another possible homozygous genotype, bb, which would result in blonde hair.

Sorry, that was kind of long. In summary:
Homozygous: Same alleles (Both dominant or both recessive).

Heterozygous: Different alleles (One dominant and another recessive).

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Post by xllxashleexllx » Tue Apr 25, 2006 5:18 pm

Khaiy wrote:Sure. A phenotype is just what trait is expressed in an organism. For example, I have brown hair, and so I display the brown hair phenotype.

Genotype is just the gene combination of an individual. Let's stick with hair for an example: My phenotype is brown, but that could be the result of different genotypes. Let's say that the allele for brown hair is dominant over the allele for blonde hair (So the brown hair allele is B, and the blonde hair allele is b). My brown hair phenotype could have come from having only brown hair alleles (genotype BB), or from having one brown allele and one blonde allele (Bb). But if I had blonde hair, then we would know that my genotype was bb.

Homozygous and heterozygous are descriptions of genotype. If I were homozygous for brown hair, then that means that both of the alleles I had would be the same (homo=same), and would code for brown hair. If I were heterozygous (heter=different), then that would mean that I had two different alleles, in this case the brown allele B and the blonde allele b. There is also another possible homozygous genotype, bb, which would result in blonde hair.

Sorry, that was kind of long. In summary:
Homozygous: Same alleles (Both dominant or both recessive).

Heterozygous: Different alleles (One dominant and another recessive).

Thank you soo much. I actually could understand this time.

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