Download Multiple Alleles and Polygenic Inheritance A. Multiple alleles

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Multiple Alleles and
Polygenic Inheritance
… a huge variety!
A. Multiple alleles
 Genes having more than two alleles
 Note: this does not mean that an
individual can have more than two
alleles. (One from Mom, one from
Dad.) It only means that more than
two possible alleles exist in a
population
 Example 1: Screech owl colors
 Example 2: Human blood type
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Screech Owls
 A recent study suggests that in
screech owls, red (R) is dominant to
brown (R’), which is dominant to grey
( r ). Also abbreviated by:
 R > R’ > r
 Is it possible for a red owl and a
brown owl to have a grey baby?
Show with Punnett square(s), or
explain in words.
Solution
  Red: R R, RR’, Rr
  Brown: R’R’, R’r
  Grey: rr
R’
r
R
RR’
Rr
r
R’r
rr
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ABO Blood Types
  Multiple alleles:
 
 
IA, IB, and i
(Note: IA and IB are
codominant to each other, and
i is recessive.)
  In 1943 a young woman,
Joan Barry, sued Charlie
Chaplin for parental support
of her child.
  Charlie Chaplin's blood was
type O. The mother of the
child had type A and her
baby girl had type B blood.
  Based on blood type, could
the child have been Charlie
Chaplin's? Show with
Punnett square or explain in
words.
Solution
  Type O, Charie must have
genotype ii. Why?
  Type A, the mother must
have genotype IAi. Why?
  Type B, the baby must have
genotype IBi. Why?
  So, baby had to get an “i”
from mom (OK!), and an “IB”
from dad (Uh Oh!)
  Charlie Chaplin could NOT
have been the father.
  Charlie was found guilty and
had to pay child support,
because the blood test was
inadmissible.
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B. Polygenic Traits
  More than one gene contributes to the
expression of the trait
  For example, skin color, hair color, eye
color, height.
Height is a
polygenic trait
Skin Color
  Up to 7 genes code for skin
color. Here is an example
of the possibilities with just
3 genes:
  AA = dark
Aa = less dark
aa - light
  And similarly for the other
two genes - in all cases
dominance is incomplete
for each gene, each
contributing a certain
amount of melanin.
  Think of each “capital”
allele (A, B, C) as adding a
dose of brown paint to
white paint.
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