More Examples of Alterations in Mendelian Patterns of Inheritance

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More Examples of Alterations in Mendelian
Patterns of Inheritance
Extranuclear Inheritance
These are traits that don't yield genetic
patterns normally associated with biparental
inheritance.
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Extranuclear Inheritance
1. Maternal effect Genotype of the female
parent, not the genotype of the offspring
determines the phenotype of those offspring.

• 2. Organelle heredity (cytoplasmic inheritence)
  results from expression of genes in chloroplasts
  or mitochondria.
• Always maternal inheritance in animals
  usually in plants.
• Mitochondrial and Chloroplast DNA
• -Usually contributions from egg only.
• -Circular DNA, organized similar to
  bacteria (no chromatin).

3. Imprinting
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Maternal Effect

• Traits are under the control of nuclear gene
  products present in the cytoplasm of the egg
• mRNAs or proteins influence the early
  development of the offspring
• Classical example shell coiling in the
  hermaphrodite snail Limnaea
• -Some have dextral (right-handed) coils,
  others sinistral
• (left-handed)

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Maternal Effect
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Organelle DNA

• Chloroplasts and mitochondria contain DNA
• Carried in the cytoplasm of the egg from
  mother to offspring (no contribution from sperm
  or pollen)
• Difficult to study because
• -Many organelles are passed on
• -Function relies on organelle and
  nuclear genes

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• Types of Inheritance in Mitochondrial Disease
• Maternal Inheritance Defects in the
  mitochondrial DNA, including point mutations,
  deletions, and duplications. Contribution only
  from the mother.
• Autosomal Inheritance Defects in the
  nuclear DNA. Contributions from both parents. Can
  be dominant or recessive.
• X-linked Inheritance Defects of the X
  chromosome.

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Mitochondrial DNA (mtDNA)
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Mitochondria with Mutations
mild heteroplasty
severe heteroplasty
homoplasty
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Inheritance of Mutant Mitochondrial DNA
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Mitochondrial Inheritance
The hallmark characteristics of mitochondrial
inheritance in humans 1.affected males do
not transmit the trait to any of their children
2.affected females transmit the trait to all of
their children
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Variation in Chloroplast DNA
Variegation of leaves in plants
The leaves can be green, white or a mixture of
green and white. White leaves result from a
mutation in the genome of the chloroplasts of
these leaves that prevents the formation of
chlorophyll.
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Explanation for Variegation
1. Branches with white leaves are derived from
cells that contain only mutant chloroplasts,
branches with green leaves are derived from cells
with normal chloroplasts and branches with
variegated leaves come from cells with both
mutant and normal chloroplasts that segregate
randomly to the cells that make up the leaf.
2. Flowers on green branches produce seeds that
grow into all green plants regardless of the
source of the pollen. Flowers of white branches
always produce all white offspring and flowers of
variegated branches can produce green, white or
variegated offspring independent of the pollen
source.
3. Thus, the phenotype of the offspring is
controlled solely by the phenotype of the
maternal parent, because the mutation occurs in
the chloroplasts, which are contributed to the
embryo by the ova.
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Exceptions to Maternal Inheritance of Chloroplast
Paternal or biparental inheritance of chloroplast
DNA
Found inEuropean Larch and many conifers
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Imprinting Allows Uniparental Allele Expression
Stages of the imprinting cycle.
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Germline Erasure and Resetting of Imprinting
Testis
Erase Reset Imprinting
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Mechanisms of Imprinting
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Imprinted Genes on Mouse Chr 7