Chapter 4 Lesson 2

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Chapter 4 Lesson 2

• Modeling Inheritance

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Learning Objective

• Using your family history to predict genetic
  outcomes with phenotypes.

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Modeling Inheritance

• Two tools can be used to identify and predict
  traits among genetically related individuals.
• Punnett square using family histories to
  predict genotypes and phenotypes.
• Pedigree Creating a map using family histories
  to predict phenotypes.

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One more thing about Punnetts

• Human Gender
• XX girl
• XY boy
• You ALWAYS have a 50 chance of having a boy or
  girl EVERY time.

X X
X XX XX
Y XY XY
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Pedigrees

• A pedigree shows genetic traits that were
  inherited by members of a family.
• Pedigrees focus more on phenotypes.
• They are also used with Punnett Squares to
  determine genotypes.

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Pedigree chart
1
1
2
Normal
Affected
Female
Male
Married
3
6
7
8
5
4
Children
12
14
13
9
10
11
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Pedigrees to evaluate

• Go to page 201 and do problems 7 - 9
• 7 Not affected dd C
• 8 affected Dd B
• 9 not affected dd C

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Draw a pedigree

• One couple has a son and a daughter with normal
  pigmentation. Another couple has one son and two
  daughters with normal pigmentation. The daughter
  of the first couple has three children with the
  son of the second couple. Their son and one
  daughter have albinism their daughter has normal
  pigmentation.

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Answer

• Is albinism, recessive or dominant?
• It is recessive.
• What must the genotype be of 2 and 3? (hint
  make a Punnett Sq.)

Albino
Female
Male
1st couple
2nd couple
3
4
5
2
1
6
8
7
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Answer

• Both parents must be Aa.
• Not all their children are albino.

A a
A AA Aa
a Aa aa
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Learning Objective Part 2

• By chance, Mendel studied traits only influenced
  by one gene with two alleles. However, we know
  now that some inherited traits have
• There are more complex patterns.

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Incomplete Dominance

• Incomplete dominance produces a THIRD phenotype
  that is a blend of parents phenotype.

R red flowers
W white flowers
Red x white 100 pink
R R
W RW RW
W RW RW
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Codominance

• When BOTH alleles can be observed in the
  phenotype.
• Black horses (BB) are codominant to white horses
  (WW). The heterozygous horses (BW) is an
  appaloosa horse.

B B
W BW BW
W BW BW
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Codominance continued

• Blood types are unique because they are an
  example of
• Codominance A and B are both dominant.
• AND
• Multiple Alleles There are three different
  alleles.

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Multiple Alleles

• Some genes only have two alleles, like in
  Mendels experiments.
• However, there are genes that have more then two
  alleles.
• But remember you can still only inherit two of
  the alleles. One from each parent.

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Multiple Alleles continued

• In a Labrador retriever, coat color is determined
  by one gene with 4 alleles.
• Black is dominant to chocolate B or b.
• Yellow is recessive epitstatic E
• (when present, it blocks the black and chocolate
  alleles)

Phenotype Possible genotypes
Black BBEE, BdEE, BBEe, BbEe
Chocolate bbEE bbEe
Yellow BBee Bbee bbee
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Sex-linked

• Because the Y chromosome is shorter than the X
  chromosome it has fewer genes.
• Therefore if you are a boy you only get one copy
  of these genes. So you get what your Mom gives
  you.

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Sex-linked continued

• Examples in humans include
• Colorblindness
• Hemophilia

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Polygenic Inheritance

• When multiple genes determine the phenotype.
• Many phenotypes are possible
• Examples in humans include
• Height
• Weight
• Skin color

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Polygenic - Skin color

• There may be 100 different genes involved and
  many mutations.
• Melanin is a pigment responsible for skin color
  and is a natural sunblock.
• Lighter skin allows for more absorption of UV
  rays from sunlight. This is important for making
  vitamin C.

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Polygenic - Skin color
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Polygenic - Skin color
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Polygenic - Skin color

• The long standing, but unproven hypothesis is
  that . . .
• If you lived near the equator you needed darker
  skin to protect you from the intense UV rays . .
  .
• If you lived farther north you needed lighter
  skin to help you get more UV rays because there
  is less sunlight.

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Genes and the Environment

• Environment can affect an organisms phenotype.
• Genes effect heart disease, but so do diet and
  exercise.
• Genes affect skin color, so does exposure to
  sunlight.
• Go to page 189 and write down, on the left side
  of your notebook, two more examples of how the
  environment can affect genes.

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Learning Objective

• To learn about different types of genetic
  disorders.

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Genetic Disorders

• If a change occurs in a gene, the organism with
  the mutation may not be able to function as it
  should.
• An inherited mutation can result in a phenotype
  called a genetic disorder.

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Sickle Cell Anemia

• This disease affects millions of people world
  wide.
• About 2 million Americans have the sickle cell
  trait. About 1 in 12 are African Americans.

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Sickle Cell Continued
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Sickle Cell Continued
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Sickle Cell Continued
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Sickle Cell Continued