Monday 20 May 2013

3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance

Dominant: a dominant allele is the one that will be made
Recessive: a recessive allele will be masked by a dominant one and not visible
Homozygous: if you have two of the same alleles for a gene in one persons DNA
Heterozygous: if you have two different alleles for a gene in in someones DNA
Phenotype: what allele is expressed as a protein
Genotype: what alleles you have in your DNA for a gene
Codominance: when two alleles have equal dominance (they will both be expressed)

By expressed I mean shown as in having brown hair is brown hair allele being expressed; and by masked I mean not expressed.
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8 comments:

  1. philip11 December 2015 at 03:46

    a dominant allele is the one that will be made ??? please expand thanks

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    1. Unknown15 December 2015 at 04:18

      a dominant allele is the one that will be made because it is 'dominating' against the recessive allele. For example, brown is a dominant eye colour, so when it is up against blue (the recessive eye colour), the persons eye colour will be brown as that allele is 'dominating' against the recessive allele (blue).
      I hope this makes sense :)

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    2. Unknown29 December 2015 at 08:39

      Probably obvious, but just wanted to point out that if two recessive alleles come up, then that allele will be shown

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  2. Unknown30 December 2015 at 08:30

    the phenotype is what trait ends up being visible in the appearance. e.g if there is a heterozygous pair of alleles, B for brown eyes (dominant) and b for blue eyes (recessive) (genotype:Bb) the phenotype is what the person ends up looking like/having, so brown eyes because brown was the dominant allele

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  3. Unknown15 May 2016 at 14:11

    Although the dominant one is largely expressed the recessive one is also expressed slightly for example if you are heterozygous for the recessive cystic fibrosis then you will still have some problems but not to a great enough extent that they will cause you difficulties but the effects can still be seen

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    1. Unknown30 November 2016 at 12:30

      Dominant genes are always expressed instead of the recessive allele unless the alleles are codominant in which case they are equally expressed, which is in the case with some flower petal colours.

      Delete
  4. Mike Tsang26 June 2017 at 04:39

    The Biology Syllabus has changed…

    Here is a New blog for the 2017 Syllabus:

    http://igcse-biology-2017.blogspot.hk

    ReplyDelete
  5. SophieRice27 June 2017 at 06:20

    more at

    http://igcse-biology-notes.blogspot.hk/2017/06/317-understand-meaning-of-terms.html

    ReplyDelete

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