7C: genotypes + phenotypes

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Last updated 1:28 AM on 9/21/26
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14 Terms

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genotype

  • genotype is the genetic composition of an organism at one particular gene locus


<ul><li><p>genotype is the <strong>genetic composition </strong>of an organism at one particular gene locus</p></li></ul><p></p>
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homozygous

  • inherit two identical alleles (AA / aa)


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heterozygous

  • two different alleles (Aa)


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dominant allele

  • expressed even when there is one copy of the allele


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recessive allele

  • only expressed when two copies are present


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heterozygous advantage

  • sometimes, carrying a disadvantageous allele can give a biological advantage for an organism

    • e.g. sickle cell anemia

  • explains why harmful recessive alleles are able to persist in a population over time, hidden in advantageous heterozygotes

    • provides greater malaria resistance


<ul><li><p>sometimes, carrying a <strong>disadvantageous allele </strong>can give a <strong>biological advantage </strong>for an organism </p><ul><li><p>e.g. sickle cell anemia </p></li></ul></li><li><p>explains why <strong>harmful recessive alleles</strong> are able to persist in a population over time, hidden in <strong>advantageous heterozygotes </strong></p><ul><li><p>provides <strong>greater malaria resistance </strong></p></li></ul></li></ul><p></p>
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phenotype

  • observable characteristics

    • genotype → directly influence genotype

      • also influences by environment → susceptible to change over time

  • genotype + environment = phenotype


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complete dominance

  • pattern of dominance where only the dominant allele from the genotype of a heterozygous individual is expressed in the phenotype of that organism


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co-dominance

  • when both alleles from the heterozygous genotype are fully or equally expressed in the phenotype

    • both alleles can be dominant and neither allele can mask the expression of the other allele

  • e.g. ABO blood system


<ul><li><p>when both alleles from the heterozygous genotype are fully or <strong>equally</strong> expressed in the phenotype </p><ul><li><p>both alleles can be <strong>dominant</strong> and <strong>neither</strong> allele can mask the expression of the other allele </p></li></ul></li><li><p>e.g. ABO blood system </p></li></ul><p></p>
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human blood system

  • co-dominant

    • blood type O is recessive to both A and B alleles

    • neither allele A nor B show dominance over the other


<ul><li><p>co-dominant </p><ul><li><p>blood type O is <strong>recessive</strong> to both <strong>A and B alleles </strong></p></li><li><p>neither allele A nor B show <strong>dominance</strong> over the other </p></li></ul></li></ul><p></p>
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incomplete dominance

  • neither allele is fully expressed in the phenotype

    • ‘blending’ of both alleles

  • e.g. red + white → pink


<ul><li><p><strong>neither</strong> allele is <strong>fully expressed </strong>in the phenotype </p><ul><li><p>‘blending’ of both alleles </p></li></ul></li><li><p>e.g. red + white → pink </p></li></ul><p></p>
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lethal alleles

  • mutation to a gene causing an allele of that gene to cause great harm if homozygous

    • e.g. HH Huntington’s disease or cc cystic fibrosis

      • if lethal combination is homozygous dominant then predicted phenotype → 2 dominant : 1 recessive


<ul><li><p>mutation to a gene causing an allele of that gene to cause <strong>great harm</strong> if <strong>homozygous </strong></p><ul><li><p>e.g. HH Huntington’s disease or cc cystic fibrosis </p><ul><li><p>if lethal combination is homozygous dominant then predicted phenotype → 2 dominant : 1 recessive </p></li></ul></li></ul></li></ul><p></p>
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sex-linked inheritance

  • present on sex chromosomes


<ul><li><p>present on sex chromosomes </p></li></ul><p></p>
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sex-linked inheritance in other animals

  • e.g. females: ZW, male ZZ

    • males can be homozygous or heterozygous and female → hemizygous

      • hemizygous = a cell or organism that has only one copy of a gene or chromosome segment instead of the usual two copies found in a normal pair