today: some things mendel did not tell us... exam #3 t 12/2 in class, final sat. 12/6
TRANSCRIPT
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
Single genes controlling a single trait are unusual. Inheritance of most genes/traits is much more complex…
Dom. Rec. Rec. Dom.
PhenotypeGenotype
Genes code for proteins (or RNA). These gene products give rise to traits…
It is rarely this simple.
Fig 4.4
Fig4.7
Sickle-cell anemia is caused by a point mutation
Sickle and normal red blood cells Fig4.7
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
Coincidence of malaria and sickle-cell anemia
Fig 24.14
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
The relationship between genes and traits is often complex
Complexities include:
• Complex relationships between alleles
Sex determination is normally inherited by whole chromosomes or by number of chromosomes.
Fig 3.18
X/Y chromosomes in humans
The X chromosome has many genes; the Y chromosome only has genes for maleness.
Human sex chromosomes
(includes Mic2 gene)
Fig 4.14
Sex-linked traits are genes located on the X chromosome
Color Blind Test
Sex-linked traits: Genes on the X chromosome
No one affected, female carriers
A= normal; a= colorblind
colorblindnormal
similar to Fig 4.13
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
Sex-linked traits: Genes on the X chromosome
50% males affected, 50% females affected
A= normal; a= colorblind
colorblindnormal
similar to Fig 4.13
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
males and females may have different numbers of chromosomes
Fig 3.18
Tbl 7.1
dosage compensation
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
Promotes compaction
Prevents compaction
Mammalian X-inactivation involves the interaction of 2 overlapping genes.
The Barr body is replicated and both
copies remain compacted
Barr body compaction is heritable within an individual
• 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
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
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
Genomic Imprinting:Methylation of genes during gamete production.
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
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
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
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
Thus genomic imprinting is permanent in the somatic cells of an animal
–However, the marking of alleles can be altered from generation to generation
• 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