Download Inheritance Patterns - Bergen County Technical Schools

Inheritance Patterns
Many inherited disorders in humans are
controlled by a single gene. All of our somatic
cells possess two copies of each gene, one
inherited from your mother and one inherited
from your father.
46,XY male karyotype
Most inherited disorders are caused
by autosomal recessive alleles
– Autosomes are the 22 pairs
of chromosomes that are not
the sex chromosomes
– Alleles are all of the alternate
forms of a gene (ie. B and b)
– Recessive means it takes two
abnormal copies to exhibit the
full blown phenotype
– Examples of autosomal
recessive disorders are :
cystic fibrosis,
sickle-cell disease, PKU
– A Punnet Square
demonstrating inheritance of
an autosomal recessive
deafness is found at the right
Normal
Dd
PARENTS
Normal
Dd
D
D
Eggs
Sperm
DD
Normal
d
OFFSPRING
d
Dd
Normal
(carrier)
Dd
Normal
(carrier)
dd
Deaf
Figure 9.9A
Found on Chromosome 12
• A few inherited disorders are caused by
dominant alleles. Dominant alleles hide
recessive alleles, phenotypically.
– Examples: achondroplasia, Huntington’s disease
Figure 9.9B
Autosomal Dominant Inheritance
Table 9.9
Sex-linked disorders affect
mostly males
• Most sex-linked human
disorders are due to
recessive alleles
• These sex linked alleles are forms of genes
found on the X chromosome. A male has
only one X chromosome
– Examples: hemophilia,
red-green color blindness
– These are mostly seen in males, but can
be seen in females.
– A male receives a single X-linked allele
from his mother, and will have the
disorder, while a female has to receive the
allele from both parents to be affected
Figure 9.23A
– Their inheritance pattern reflects the fact that
males have one X chromosome and females
have two
– These figures illustrate inheritance patterns for
white eye color (r) in the fruit fly, an X-linked
recessive trait
Female
XRXR
Male
Xr Y
XR
Female
XRXr
Xr
XRXr
Male
XRY
XRY
Xr
XRXR
XrXR
XRY
XrY
R = red-eye allele
r = white-eye allele
Male
XRXr
XR
XR
Y
Female
XrY
Xr
XR
Y
Xr
XRXr
Xr Xr
Y
XRY
XrY
Figure 9.22B-D
X-Linked Recessive Inheritance
X-Linked Dominant Inheritance
Incomplete dominance results in
intermediate phenotypes
• When an offspring’s
phenotype—such
as flower color— is
in between the
phenotypes of its
parents, it exhibits
incomplete
dominance
P GENERATION
White
rr
Red
RR
Gametes
R
r
Pink
Rr
F1 GENERATION
1/
1/
Eggs
1/
F2 GENERATION
2
2
2
R
1/
2
r
1/
R
R
Red
RR
r
Pink
Rr
Sperm
1/
Pink
rR
White
rr
Figure 9.12A
2
2
r
• Incomplete dominance in human
hypercholesterolemia (high levels of
cholesterol in the blood)
GENOTYPES:
HH
Homozygous
for ability to make
LDL receptors
Hh
Heterozygous
hh
Homozygous
for inability to make
LDL receptors
PHENOTYPES:
LDL
LDL
receptor
Cell
Normal
Figure 9.12B
Mild disease
Severe disease
Codominance-The individual expresses
both phenotypes and neither is
dominant.
Type AB express both antigens
Mitochondrial Gene Inheritance
Mitochondrial Disorders
Mitochondrial Disorders
•Depletion of mtDNA
Infantile myopathy
Fatal
"Later-onset"
AZT treatment
Several types of mtDNA
defect
Deafness
Diabetes
External ophthalmoplegia
(PEO)
Sporadic
Maternal
Dominant
Recessive
Leigh's
Myopathy
Rhabdomyolysis
Sensory neuropathy
Systemic disorders
•
mtDNA Point mutations
Cardiomyopathy
Leber's optic neuropathy
Leigh's syndrome
MELAS
MERRF
NARP/MILS
Single deletion or duplication
Ataxia, Leukodystrophy
Diabetes: Maternal
inheritance
Kearns-Sayre
Pearson's
PEO: Sporadic
Multiple deletions
Aging
Myositis
Inclusion body
COX- muscle fibers
MNGIE
PEO
Wolfram
Mitochondrial Inheritance
Mitochondrial disease begins to become
apparent once the number of affected
mitochondria reaches a certain level; this
phenomenon is called 'threshold
expression'.
In class……………………….
• What is the mode of inheritance of the
disorder you are researching?
• If you are studying a particular cell type,
are there diseases associated with this cell
type when it is mutated and how are those
diseases inherited?