The Chromosome Theory of Inheritance

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The Chromosome Theory of Inheritance
Chpt. 15 .
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1866 Mendels paper
Putting the pieces together
1875 process of mitosis revealed
1890 process of meiosis revealed
1902 realization that chromosomes were Mendels
factors
ONLY 36 YEARS!!!
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Sex chromosomes- Autosomes
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Sex chromosomes- vary within species --gt --gt
--gt
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Sex chromosomes-
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In 1902 Sutton suggested that "the association of
paternal and maternal chromosomes in pairs and
their subsequent separation during the reduction
division...may constitute the physical basis of
the Mendelian law of heredity." His "The
Chromosomes in Heredity" was published in 1903.
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• Walter Sutton 1902
• Genes have specific locations (loci) on
  chromosomes
• chromosomes undergo segregation and independent
  assortment.
• The Chromosome Theory of Inheritance

... but you already knew that!
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tracking 2 genes on different chromosomes in
their homologous pairs.
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Thomas Hunt -Morgan
1st to associate specific genes on specific
chromosomes
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• Thomas Hunt Morgan
• UtilizedDrosophila melanogaster
• fruit fly
• 3 pairs autosomes
• 1 pair sex chromosomes

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• Thomas Hunt Morgan
• Utilized Drosophila melanogaster
• can reproduce a generation in two weeks.

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Fruit Fly Chromosomes
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Genetic Symbols

• Mendel - use of uppercase or lowercase letters.
• T tall
• t short
• Morgan symbol from the mutant phenotype (for
  fruitflies).
• wild phenotype (predominant)

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Examples

• Recessive mutant
• w white eyes
• w red eyes
• or red eyes

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Examples

• Mutant
• Cy Curly wings
• Wild Type
• Cy Normal wings

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• Evidence for Sex Linkage
• female red eyes X male white eyes
• F1 --gt 40 RED

red dominant
You would expect this with Mendel would you not?
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Evidence for Sex Linkage female red eyes X
male red eyes
red dominant
F2 --gt 31 BUT ONLY males had white eyes??
F2
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eye color linked to gender
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Examples

• Recessive mutant
• w white eyes
• w red eyes
• or red eyes

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• eye color linked to gender
• 50 males had red eyes.
• 50 males had white eyes.

0 females had white eyes.
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• Evidence for Sex Linkage
• 50 males had red eyes.
• 50 males had white eyes.
• 0 females had white eyes.

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Fruit Fly Chromosomes
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Linked Genes
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• Linked Genes (not sex-linked genes)
• Genes are on the same chromosome, therefore
  passed along as a unit

A
B

• Ratios mimic monohybrid crosses.. But it is a
  dihybrid cross.

these DEVIATE from Mendels norm
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Linked Genes (not x-linked)
1111
5511
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IF genes are linked, we would NOT expect any
offspring to have different characters from that
of the parents
THAT was not the case though, the offspring were,
in fact different
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Well now, THATs confusing
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Linked Genes (not x-linked)
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Somethings goofy
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Recombination due to crossing over in
linked genes
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YES!!! I remember this stuff!!
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Crossing-Over

• Breaks up linkages and creates new ones.
• Recombinant offspring formed that doesn't match
  the parental types.

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Alfred Sturtevant
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• Recombination Frequency
• of recombinants total
  offspring
• gives a rough estimate of how often recombination
  occurs.
• used to map genes in relation to one another.

X 100
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• Recombination Frequency
• The farther apart two genes, the higher the
  probability that a X-over will occur.
• The higher the Recombination Frequency

... but you already knew that!

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YES!!! I remember this stuff!!
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b - vg 17
b - r 7.5
r - vg 9.5
Map of 3 genes relative to each other (genes b,
r, vg)
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b - vg 17
b - r 7.5
r - vg 9.5
b
vg
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7.5
Map of 3 genes relative to each other
(genes b, r, vg)
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b - vg 17
b - r 7.5
r - vg 9.5
b
r
vg
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7.5
Map of 3 genes relative to each other
(genes b, r, vg)
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b - vg 17
b - r 7.5
r - vg 9.5
b
r
vg
17
7.5
9.5
Map of 3 genes relative to each other
(genes b, r, vg)
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Map of 3 genes relative to each other
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Map of 3 genes relative to each other
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• Gene Map -
• Relative position using map units.
• Obtained from Recombination Frequency Data

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Girls must be more powerful b/c girls get two
X's and boys only get one!!!
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Actually, one X becomes inactive during
embryonic development
Barr Body
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Calico Cats.
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Calico Cats.
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Actually, one X becomes inactive during
embryonic development

• Result - body cells are a mosaic of X types.

Barr Body