Single genes controlling a single trait are unusual. Inheritance of most genes/traits is much more complex

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Single genes controlling a single trait are
unusual. Inheritance of most genes/traits is
much more complex
Dom.
Rec.
Rec.
Dom.
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Phenotype
Genotype
Genes code for proteins (or RNA). These gene
products give rise to traits It is rarely this
simple.
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Fig 4.4
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Sickle-cell anemia is caused by a point mutation
Fig4.7
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Fig4.7
Sickle and normal red blood cells
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Fig4.7
Sickle-Cell Anemia A dominant or recessive
allele?
Ssickle-cell Hnormal
Mom HS
Dad HS
Dad
H or S
possible offspring 75 Normal 25 Sickle-cell
HS
HH
H or S
Mom
HS
SS
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Coincidence of malaria and sickle-cell anemia
Fig 24.14
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Fig4.7
Sickle-Cell Anemia A dominant or recessive
allele?
Ssickle-cell Hnormal
Mom HS
Dad HS
possible offspring Oxygen transport 75
Normal 25 Sickle-cell Malaria resistance 75
resistant 25 susceptible
Dad
H or S
HS
HH
H or S
Mom
HS
SS
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The relationship between genes and traits is
often complex

• Complexities include
• Complex relationships between alleles

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Fig 3.18
Sex determination is normally inherited by whole
chromosomes or by number of chromosomes.
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X/Y chromosomes in humans
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The X chromosome has many genes the Y chromosome
only has genes for maleness.
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Human sex chromosomes
Fig 4.14
(includes Mic2 gene)
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Sex-linked traits are genes located on the X
chromosome
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Color Blind Test
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Sex-linked traits Genes on the X chromosome
A normal a colorblind
colorblind
normal
No one affected, female carriers
similar to Fig 4.13
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Sex-linked traits Genes on the X chromosome
A normal a colorblind
normal
normal
50 of males affected, 0 females affected
similar to Fig 4.13
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Sex-linked traits Genes on the X chromosome
A normal a colorblind
colorblind
normal
50 males affected, 50 females affected
similar to Fig 4.13
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Sex-linked traits Genes on the X chromosome
A normal a colorblind
No one affected, female carriers
50 of males affected, 0 female affected
50 males affected, 50 females affected
similar to Fig 4.13
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Fig 3.18
males and females may have different numbers of
chromosomes
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Tbl 7.1
dosage compensation
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Fig 7.4
The epithelial cells derived from this embryonic
cell will produce a patch of white fur
At an early stage of embryonic development
While those from this will produce a patch of
black fur
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Mammalian X-inactivation involves the interaction
of 2 overlapping genes.
Promotes compaction
Prevents compaction
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• A few genes on the inactivated X chromosome are
  expressed in the somatic cells of adult female
  mammals
• Pseudoautosomal genes(Dosage compensation in
  this case is unnecessary because these genes are
  located both on the X and Y)
• Up to a 25 of X genes in humans may escape full
  inactivation
• The mechanism is not understood

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Lamarck was right? Sort of
Epigenetics http//www.pbs.org/wgbh/nova/science
now/3411/02.html
Image from http//www.sparknotes.com/biology/evol
ution/lamarck/section2.rhtml
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Genomic Imprinting

• Genomic imprinting is a phenomenon in which
  expression of a gene depends on whether it is
  inherited from the male or the female parent
• Imprinted genes follow a non-Mendelian pattern of
  inheritance
• Depending on how the genes are marked, the
  offspring expresses either the maternally-inherite
  d or the paternally-inherited allele Not both

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Genomic Imprinting Methylation of genes during
gamete production.
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A hypothetical example of imprinting
a B
a B
A b
Acurly hair astraight hair Bbeady
eyes bnormal methylation A in males B in
females
A b
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A hypothetical example of imprinting
a B
a B
A b
Acurly hair astraight hair Bbeady
eyes bnormal methylation A in males B in
females
A b
Aa bB
Aa bB
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A hypothetical example of imprinting
a B
a B
A b
Acurly hair astraight hair Bbeady
eyes bnormal methylation A in males B in
females
A b
Aa bB
Aa bB
Aa bB
Aa bB
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A hypothetical example of imprinting
similar to Fig 7.10
a B
a B
A b
Acurly hair astraight hair Bbeady
eyes bnormal methylation A in males B in
females
A b
Aa bB
Aa bB
Aa bB
Aa bB
Ab, AB, ab, aB
Ab, AB, ab, aB
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• Thus genomic imprinting is permanent in the
  somatic cells of an animal
• However, the marking of alleles can be altered
  from generation to generation

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Imprinting and DNA Methylation

• Genomic imprinting must involve a marking process
• At the molecular level, the imprinting is known
  to involve differentially methylated regions
• They are methylated either in the oocyte or sperm
• Not both