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