today: some things mendel did not tell us... exam #3 t 12/2 in class, final sat. 12/6
TRANSCRIPT
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Today: some things Mendel did not tell us...Today: some things Mendel did not tell us...Exam #3 T 12/2 in class, Final Sat. 12/6Exam #3 T 12/2 in class, Final Sat. 12/6
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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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PhenotypeGenotype
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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Fig4.7
Sickle-cell anemia is caused by a point mutation
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Sickle and normal red blood cells Fig4.7
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Mom = HS Dad = HS
H or S
H or S
HH
HS SS
HS possible offspring75% Normal25% Sickle-cell
Mom
Dad
S=sickle-cell
H=normal
Sickle-Cell Anemia:A dominant or recessive allele?
Fig4.7
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Coincidence of malaria and sickle-cell anemia
Fig 24.14
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Mom = HS Dad = HS
H or S
H or S
HH
HS SS
HS
possible offspringOxygen transport:75% Normal25% Sickle-cell
Malaria resistance:75% resistant25% susceptible
Mom
Dad
Sickle-Cell Anemia:A dominant or recessive allele?
S=sickle-cell
H=normal
Fig4.7
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The relationship between genes and traits is often complex
Complexities include:
• Complex relationships between alleles
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Sex determination is normally inherited by whole chromosomes or by number of chromosomes.
Fig 3.18
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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
(includes Mic2 gene)
Fig 4.14
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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
No one affected, female carriers
A= normal; a= colorblind
colorblindnormal
similar to Fig 4.13
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Sex-linked traits: Genes on the X chromosome
50% of males affected, 0 % females affected
A= normal; a= colorblind
normalnormal
similar to Fig 4.13
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Sex-linked traits: Genes on the X chromosome
50% males affected, 50% females affected
A= normal; a= colorblind
colorblindnormal
similar to Fig 4.13
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Sex-linked traits: Genes on the X chromosome
No one affected, female carriers
50% of males affected, 0 % female affected
50% males affected, 50% females affected
A= normal ; a= colorblind
similar to Fig 4.13
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males and females may have different numbers of chromosomes
Fig 3.18
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Tbl 7.1
dosage compensation
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At an early stage of embryonic development
The epithelial cells derived from this
embryonic cell will produce a patch of
white fur
While those from this will produce a patch of black fur
Fig 7.4
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Promotes compaction
Prevents compaction
Mammalian X-inactivation involves the interaction of 2 overlapping genes.
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The Barr body is replicated and both
copies remain compacted
Barr body compaction is heritable within an individual
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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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Epigenetics: http://www.pbs.org/wgbh/nova/sciencenow/3411/02.html
Lamarck was right? Sort of…
Image from: http://www.sparknotes.com/biology/evolution/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-inherited 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=curly hair
a=straight hair
B=beady eyes
b=normal
*=methylation
A* in males
B* in females
aB*
aB* A*
bA*b
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A hypothetical example of imprinting
A=curly hair
a=straight hair
B=beady eyes
b=normal
*=methylation
A* in males
B* in females
A*abB*
A*abB*
aB*
aB* A*
bA*b
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A hypothetical example of imprinting
A=curly hair
a=straight hair
B=beady eyes
b=normal
*=methylation
A* in males
B* in females
A*abB*
A*abB*
A*abB
AabB*
aB*
aB* A*
bA*b
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A hypothetical example of imprinting
A=curly hair
a=straight hair
B=beady eyes
b=normal
*=methylation
A* in males
B* in females
A*abB*
A*abB*
A*abB
AabB*
A*b, A*B,ab, aB
Ab, AB*,ab, aB*
aB*
aB* A*
bA*b
similar to Fig 7.10
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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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• 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
Imprinting and DNA Methylation