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Complex Inheritance

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Complex Inheritance & Dihybrid Crosses Complex Inheritance Patterns If all traits were controlled by only two alleles and one was dominant and the other was recessive ... – PowerPoint PPT presentation

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Title: Complex Inheritance


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Complex Inheritance Dihybrid Crosses
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Complex Inheritance Patterns
  • If all traits were controlled by only two alleles
    and one was dominant and the other was recessive,
    it would be easy to predict the traits of
    offspring. But this is not the case think about
    traits in which there is A LOT of variation or
    where alleles seem to blend together to produce
    a phenotype that is somewhere in between the
    homozygous dominant and homozygous recessive
    phenotypeshow are these inherited???

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  • Incomplete Dominance
  • Individuals who are heterozygous have a phenotype
    that is a mixture of the 2 homozygous
    phenotypes.
  • Ex Snapdragons can have red or white flowers if
    they are homozygous. However if you cross a red
    and white flower together you get pink offspring!
  • OR Straight curly hair ? Wavy hair

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When you do a punnetts sq - still use 1 letter
to represent the gene -only know its incomplete
because you get a blended phenotype.
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Codominance Individuals who are heterozygous
will show the phenotypes of BOTH homozygous
individuals. They do not MIX (blend) into a new
color.
  • Both colors are represented so each gets its own
    capital letter. If this was incomplete the
    chicken would be? _________
  • Ex Chickens who are homozygous can have black
    feathers (BB) or white feathers (WW).
    Individuals who have the heterozygous genotype
    (BW) will have BOTH black feathers AND white
    feathers.

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  • What if hair was controlled by codominance?
  • Straight curly
  • both!

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  • Multiple Alleles
  • Many genes have more than 2 possible alleles in a
    population.
  • In this case, each individual still inherits only
    2 alleles (one from each parent) but in the
    population as a whole, there are more than 2
    possibilities.
  • NOTE they are all the same gene but since it has
    many alleles the alleles get a super script.

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  • Example 3 Color Coat in Rabbits (pg 273)
  • C full color, dominant to all alleles (brownish)
  • cch chinchilla (grayish) dominant to ch and c
    alleles
  • ch Himalayan (white with black feet, ears,
    nose) dominant to c allele
  • c albino recessive to all other alleles

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  • What are the phenotypes for the following
    genotypes?
  • CC
  • Ccch
  • cch ch
  • ch c

full brown
full brown
chinchilla
Himalayan
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  1. The interesting case of blood type in
    humansblood type has a 2 different inheritance
    patterns

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  • There are 3 possible alleles to inherit for blood
    typethe A, B and O allele.
  • We symbolize the A allele as IA
  • We symbolize the B allele as IB
  • We symbolize the O allele as i
  • The A and B alleles are dominant to the i allele.
    However, the A allele and the B allele are also
    codominant when inherited together.
  • Write all the different genotypes possible for
    each phenotypes of blood using the chart!

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ANSWERS
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  • HW is to complete all of the practice problems
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