Title: Single genes controlling a single trait are unusual. Inheritance of most genes/traits is much more complex
1(No Transcript)
2Single genes controlling a single trait are
unusual. Inheritance of most genes/traits is
much more complex
Dom.
Rec.
Rec.
Dom.
3Phenotype
Genotype
Genes code for proteins (or RNA). These gene
products give rise to traits It is rarely this
simple.
4Fig 4.4
5Sickle-cell anemia is caused by a point mutation
Fig4.7
6Fig4.7
Sickle and normal red blood cells
7Fig4.7
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
8Coincidence of malaria and sickle-cell anemia
Fig 24.14
9Fig4.7
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
10The relationship between genes and traits is
often complex
- Complexities include
- Complex relationships between alleles
11Fig 3.18
Sex determination is normally inherited by whole
chromosomes or by number of chromosomes.
12X/Y chromosomes in humans
13The X chromosome has many genes the Y chromosome
only has genes for maleness.
14Human sex chromosomes
Fig 4.14
(includes Mic2 gene)
15Sex-linked traits are genes located on the X
chromosome
16Color Blind Test
17Sex-linked traits Genes on the X chromosome
A normal a colorblind
colorblind
normal
No one affected, female carriers
similar to Fig 4.13
18Sex-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
19Sex-linked traits Genes on the X chromosome
A normal a colorblind
colorblind
normal
50 males affected, 50 females affected
similar to Fig 4.13
20Sex-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
21Fig 3.18
males and females may have different numbers of
chromosomes
22Tbl 7.1
dosage compensation
23Fig 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
24Mammalian X-inactivation involves the interaction
of 2 overlapping genes.
Promotes compaction
Prevents compaction
25(No Transcript)
26- 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
27Lamarck 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
28Genomic 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
29Genomic Imprinting Methylation of genes during
gamete production.
30A 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
31A 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
32A 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
33A 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
34- Thus genomic imprinting is permanent in the
somatic cells of an animal - However, the marking of alleles can be altered
from generation to generation
35Imprinting 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