COMPLEX PATTERNS OF INHERITANCE Patterns of inheritance that do NOT follow Mendel’s law

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  • COMPLEX PATTERNS OF INHERITANCEPatterns of inheritance that do NOT follow Mendels law.

  • Review Mendels Simple GeneticsThere are 2 alleles for each trait.An allele is either Dominant Which is represented by upper case, D.The phenotype is visible w/just one allele.So the phenotype is visible with either a heterozygous or a homozygous genotype.Or RecessiveWhich is represented by lower case, d.The phenotype is visible ONLY w/2 recessive alleles: thats the homozygous recessive genotype.

  • Review Mendels Simple GeneticsMendels Law of Segregation: these alleles will separate from each other during the formation of gametes.

    Mendels law of Independent Assortment: theses alleles will be assorted into the newly formed gametes independently of each other.

  • Incomplete DominanceThe phenotype of the heterozygote is in between those of the two homozygotes.

    It is an intermediate, and a third phenotype appears when the heterozygote is present

    In heterozygotes, neither allele is completely dominant.

  • Example-SnapdragonsRR = RedRR = WhiteRR = Pink R RR


  • CODOMINANCEThe phenotypes of both alleles are equally expressed in the heterozygote.

    Example: Horses

    HRHR = Red Horse

    HWHW = White Horse

    HRHW = Roan Horse



  • RedHorseWhiteHorseRoanHorseCODOMINANCE

  • Multiple AllelesTraits controlled by more than 2 alleles (more than 2 phenotypes)

    A diploid individual can only have 2 alleles of a trait.

    Example: Blood type = 3 different alleles: IA, IB, i

  • Multiple Alleles

    Blood TypeBlood Type That Can Be ReceivedType of Antigens PresentType of Antibodies ProducedA ( IA )A and OA antigensB antibodiesB ( IB )B and OB antigensA antibodiesO ( i )Universal DonorOnly ONo antigensA and B antibodiesAB ( IAIB ) Universal RecipientAll typesA and B antigensNo antibodies


    HRGenes can be on the same chromosome or on different chromosomes.

    Phenotypes usually show a continuous range or variability.

    - Example: Height = A, B, and C all contribute to height.

    Polygenic Traits

  • AaC cBbTallest = AABBCC

    Shortest = aabbcc

    In between = AbBbCc

    Polygenic traits include: skin color, body weight, eye color, hair color, and height.Polygenic traits