Inheritance of Traits

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Inheritance of Traits

• Probability
• Carriers
• Autosomal
• Sex-linked
• Pedigrees
• Complex patterns of heredity
• Incomplete dominance
• Codominance
• Multiple Alleles
• Practice

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Inheritance of Traits

• Probability- the likelihood that a specific event
  will occur
• When you flip a coin, there is a 50/50 chance it
  will land tails side up
• If there are 4 kids in a family, probability says
  2 will be girls and the other 2 will be boys

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Inheritance of Traits

• Carrier- an individual who is heterozygous for an
  inherited disorder but does not show symptoms.
• Ex. Linda is a carrier for albinism.
• Genotype-(Aa)
• Phenotype- not albino
• Even though she does not display the symptoms,
  she can still pass on albinism to her children.

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Inheritance of Traits

• Autosomal- when a gene is autosomal, it will
  appear in both sexes
• Sex-linked- when a gene is sex-linked, it is
  found only on the X or Y chromosomes so the
  effects are only seen in males.
• Remember, males are (Xy) and females are (XX)
• Examples- colorblindness, hemophilia, Cystic
  Fibrosis and Sickle Cell Anemia

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Inheritance of Traits

• Sex-linked Punnett Square for colorblindness

X
X
Key XX- female Xy- male Xby- colorblind
male XXb- female carrier XbXb- colorblind female
Xb
y
What are the offspring?
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Inheritance of Traits

• Sex-linked Punnett Square for colorblindness

X
Xb
Key XX- female Xy- male Xby- colorblind
male XXb- female carrier XbXb- colorblind female
X
y
What are the offspring?
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Inheritance of Traits

• Sex-linked Punnett Square for colorblindness

Xb
X
Key XX- female Xy- male Xby- colorblind
male XXb- female carrier XbXb- colorblind female
Xb
y
What are the offspring?
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Pedigrees

• Pedigree- a family history that shows how a trait
  is inherited over several generations
• Useful to track the carriers of genetic disorders
  in families
• Can be used for both autosomal and sex-linked
  disorders

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Pedigrees

• Pedigree for albinism

The order of children is from left to right
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Pedigrees

• Pedigree for albinism

1. Which individuals are heterozygous for albinism?
2. Which are homozygous for albinism?
3. Which individuals have albinism?
4. Which generations have an individual with
   albinism?

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Complex Patterns of Heredity

• Polygenic inheritance- when several genes
  influence a characteristic
• Incomplete dominance
• Codominance
• Multiple alleles

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Complex Patterns of Heredity

• Incomplete dominance- when an individual displays
  an intermediate/middle phenotype of the parents
• Ex. A red (RR) snapdragon flower is crossed with
  a white (rr) one and their offspring are pink
  (Rr)

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Complex Patterns of Heredity

• Codominance- when two dominant alleles are
  expressed at the same time
• Ex. Blood types- AB blood

A
A
B
AB
AB
AB
AB
B
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Complex Patterns of Heredity

• Codominance
• Ex. Roan horses (have both red and white hair)

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Complex Patterns of Heredity

• Multiple alleles- genes with 3 or more possible
  alleles
• Ex. Blood types- A, B, O (AB- codominant)

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PracticeBlood Type

• If a man is homozygous for type B blood, and has
  a child with a homozygous woman with type A
  blood, what are the possible blood types of the
  child?

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PracticeBlood type

• A man is heterozygous for type A blood and has a
  child with a woman that has AB blood. What are
  the possible blood types of the child?

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PracticeIncomplete dominance

• Assume
• Red RR
• White rr or WW or RR
• Pink Rr or RW or RR
• You cross a red flower with a white flower

What happens?