Incomplete Dominance

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Incomplete Dominance

• Neither allele for a trait is dominant.
• The phenotype produced is intermediate between
  the two homozygous parents.

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Multiple Alleles

• More than two alleles are multiple alleles.
• Traits controlled by multiple alles produce more
  than three phenotypes.

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Multiple Genes
Coat color genes in mammals
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AaBb
F1
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AB
Ab
aB
ab
AB
Ab
aB
ab
A_B_ agouti A_bb cinnamon aaB_ black
aabb brown
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Polygenic Inheritance

• A group of gene pairs acts together to produce a
  trait, which creates more variety in phenotypes.
• Many human traits are controlled by polygenic
  inheritance, such as hair and eye color.

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Polygenic Inheritance Skin Color
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Mutations

• Genes that are altered or copied incorrectly.
• A mutation can be harmful, beneficial, or have no
  effect.

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Down Syndrome

• Down syndrome is caused by an extra copy of
  chromosome 21

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Recessive Genetic Disorders

• Both parents have a recessive allele responsible
  for the disorder and pass it on to their child.
• Because the parents are heterozygous, they dont
  show any symptoms.

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Cystic Fibrosis
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Manx gene in cats Mm tail-less mm normal MM
dead
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Sex-linked Genes

• Genes that determine the sex of an organism are
  XX in females and XY in males.
• Females produce eggs with an X Chromosome ONLY!
• Males produce sperm with either an X or a Y
  chromosome.

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Sex-linked disorders

• An allele inherited on an X or Y chromosome is
  called a sex-linked gene.
• Color blindness is a sex-linked disorder caused
  by a recessive allele on the X chromosome.

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Pedigree

• Follows a trait through generations of a family.
• Circle family
• Square male

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