Warm-up

1
Warm-up

• In humans
• T ability to roll the tongue
• t inability to roll the tongue
• E unattached earlobes
• e attached earlobes
• TtEE x Ttee
• What are the potential genotypes and phenotypes
  of the offspring? (yes, draw a punnett square)

2
Patterns of Inheritance

• 11.3

3
Incomplete Dominance

• One allele is not completely dominant over
  another allele.
• A heterozygous phenotype will appear as a blend
  of the two homozygous phenotypes.
• Examples Snap Dragon Flower Color
• Genes may be identified in multiple ways
• Red R
• White r or R
• Pink Rr or RR

4
Example

• White horse is crossed with a chestnut brown
  horse. The offspring is golden palomino.
• Incomplete dominance

5
Codominance

• Alleles are equally dominant.
• A heterozygous phenotype will show both of the
  parental phenotypes.
• Exhibits both traits NOT a
  blend

6
Example

• A chicken with black feathers is crossed with a
  chicken with white feathers. The offspring have
  black and white checkers.
• codominance

7
Multiple Alleles

• More than two alleles for a given trait
• Each organism still inherits 2 alleles
• Example Rabbits have 4 alleles for coat color

Phenotype Agouti Chinchilla Himalayan Albino
Allele C Cch Ch c
Picture
Dominance Dominant to all alleles Dominant to Ch and c Dominant to c Recessive to all alleles
Possible Genotypes C___ Cch____ Ch___ c___
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Multiple Alleles

• More than two alleles for a given trait
• Each organism still inherits 2 alleles
• Example Mice have 3 alleles for coat color
• C or cb black (dominant to yellow and agouti)
• cy yellow (dominant to agouti, recessive to
  black)
• ca- agouti (recessive to both black and yellow)

9
Example

• In pigeons we see three feather colors ash- red,
  blue, and chocolate.
• Ash-red BA is dominant
• Blue- B -is dominant to chocolate, but recessive
  to Ash-Red
• Chocolate- b -is recessive to both Ash-red and
  Blue
• What are the potential genotypes if a Blue pigeon
  is crossed with a Blue pigeon.

10
Sex-Linked Genes

• Genes located on the sex chromosomes (usually the
  last pair of chromosomes)
• Frequently found on the X (sometimes on the Y)
• Usually recessive
• Passed from Mother to son
• Occurs more frequently in males less frequently
  in females

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Example

• Eye color in fruit flies
• Red eye color is dominant (R)
• White eye color is recessive (r)
• Always use the sex chromosomes to notate ex. XRXR
  or XRXr is a female with red eyes and XrXr is a
  female with white eyes.
• What is the genotypes for males with red eyes and
  males with white eyes?

12
What do you see?
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Polygenic Traits

• Two or more genes control the trait.
• Also referred to as continuous traits
• The result is the perception of continuous
  gradation in the expression of these traits.
• Examples Stem height in
• certain plants, many human
• examples such as skin color,
• eye color etc.

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Human examples of polygenic traits

• Skin color Eye color Hair color

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Example

• Three genes control stem height in plants
• (A, B and C)
• For all three genes the dominant allele is tall
  and the recessive allele is short.
• Therefore AABBCC is the tallest plant and aabbcc
  is the shortest plant.
• What is the probability of getting a aabbcc
  genotype from parents who are heterozygous for
  all three genes?