Download Non-Mendelian Genetics

Non-Mendelian Genetics
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For all of the inheritance patterns we will be
doing Punnett squares in class. Please leave
room in your notes to add those.
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Today, we know that genes often do not
follow Mendel’s Laws all the time! There are
exceptions…..
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Incomplete dominance
Co-dominance
Epistasis
Polygenics
Sex influenced
Sex linkage
Environmental genes
Pleiotropy
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Incomplete dominance
• Characterized by a blending of traits. Phenotype of
offspring falls somewhere between each parent, when
genotype is heterozygotic. These intermediate
offspring are called roans.
• EX: Red horses (RR) crossed with white horses (rr)
produce Rr roans that are “pink” in color.
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Co-dominance
• Characterized by the
expression of both
alleles. Even the
recessive allele affects
the organism.
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EX: Blood type - A
and B are both
dominant!
• IAIA or IAi= A type
• IAIB = AB type
B
B
B
• I I or I i = B type
• ii = O type
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Epistasis
• Characterized where one set of genes (2 alleles) covers
or overrides a totally separate set of genes (2 other
alleles).
Ex: Heterochromia iridum
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Epistasis
Ex: Albinism. If an organisms carries the albino gene (a)
no matter what genes that organism has for color, the
organism will be albino.
So a mouse with a
B=black coat genotype of BBaa
will have NO
a= albino
color!
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Polygenic traits
Characterized by many genes are needed to affect a
single trait.
Eye color
Hair color
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Sex influenced
Genes that are expressed differently based on hormones
produced by the sex chromosomes X or y.
EX: patterned baldness
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Sex linkage
Characterized by genes carried on the X or Y
chromosomes.
• If the genes are on the • Those carried on the X
y, they are called
are more abundant
holandric. Ex: Ear hair • EX: Muscular Dystrophy
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• EX: Hemophilia
• XhXh or XhY= hemophilia.
• Males CAN’T be carriers of an X-linked gene!
Lets do a
Punnett Square
to show this
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Environmental genes
Phenotype that changes as genes are exposed
to external stimuli, like temperature.
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Pleiotropy
One gene controls multiple expression.
EX: Genes for white coat color in dogs also
controls the ability to hear.
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