Inheritance of Traits

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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 equally

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Inheritance of Traits

• Sex-linked- when a gene is sex-linked, it is
  found only on the X chromosome so the effects are
  seen in males more often than females
• 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

X
Xb
Key XX- female Xy- male Xby- colorblind
male XXb- female carrier XbXb- colorblind female
Xb
y
What are the offspring?
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• Sex linked
• Sometimes you can write sex linked genotypes like
  this
• (N normal n abnormal)
• XNXN
• XNXn
• XnXn

XNy Xny
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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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Pedigree Key

• Circle- female Square- male
• Clear circle/square- does not show trait/disorder
• Shaded circle/square- has trait disorder
• Carries can be displayed several different ways
• half will be shaded
• it will be clear with a line through the middle
• it will be clear
• Horizontal line between circle and square
  indicates two married people
• Vertical line extending from a parent line leads
  to offspring
• The order of children is left to right

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Pedigrees

• Pedigree for albinism
• (autosomal)

The order of children is from left to right
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Pedigrees

• Pedigree for albinism (autosomal)

B
A
D
C
E
F
G
H
I
J
K

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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Pedigree for colorblindness (sex-linked-
X-linked Recessive Trait)
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A
F
X

• How many males are colorblind?
• How many females are colorblind?
• What is the genotype for square A?
• What is the genotype for circle F?
• Is circle F colorblind?
• What is the genotype for circle X?

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Complex Patterns of Heredity

• We have been talking about Mendelian Genetics
  where the phenotype of one allele dominants over
  another
• Now were are going to talk about Non Mendelian
  Genetics
• Intermediate inheritance
• Polygenic inheritance
• Incomplete dominance
• Codominance
• Multiple alleles

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Intermediate Inheritance

• Intermediate inheritance- when the heterozygous
  offspring (Bb, Rr, etc) display a trait that is
  not exactly like either parent
• One trait DOES NOT simply dominate over the other

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Polygenic Inheritance

• Polygenic inheritance
• Many genes contribute to the phenotype
• Provides genetic variation
• Examples
• Skin color, hair color, height

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Incomplete domiance

• Incomplete dominance- when an individual displays
  an intermediate/middle phenotype of the parents
  (neither is dominate or recessive)
• Ex. A red (RR) snapdragon flower is crossed with
  a white (rr) one and their offspring are pink
  (Rr)

R
R
r
Rr
Rr
r
Rr
Rr
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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?
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Incomplete Domiance

• Cross a red flower with a pink flower
• What happens?

R
R
R
RR
RR
r
Rr
Rr
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Codomiance

• Codominance- when two dominant alleles are
  expressed at the same time
• Ex. Roan horses or cattle
• have both red AND white hair

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Codominance Practice

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

What happens?
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Codominance

• Another example of codominance is blood type
• If someone has AB blood that means they have both
  A blood AND B blood

A
A
B
AB
AB
B
AB
AB
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Multiple Alleles

• Multiple alleles- more than 2 forms of a gene are
  expressed
• Example- rabbit coat color
• It isnt just black OR brown brown OR white
• Rabbit fur could be brown, black, white, or a
  combination of black and white

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Multiple Alleles

• Another common example of multiple alleles is
  blood type
• IAIA homozygous dominant A blood
• IAIO heterozygous dominant A blood
• IBIB homozygous dominant B blood
• IBIO heterozygous dominant B blood
• IAIB heterozygous but has both A and B blood
  (is also codominant)
• iOiO homozygous recessive

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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?