Sex Linked Flashcards
XRXR
what is the phenotype
Red-eyed female
XRXr
what phenotype
Red-eyed female
XrXr
White-eyed female
XRY
what phenotype
Red-eyed male
XrY
what phenotype
white-eyed male
are used to
predict the outcome of sexlinked inheritance.
punnett square
A “__-” is a female who is
heterozygous for the trait
carrier
This gene has its ___ on the X-chromosome, it is said to be ___
LOCUS
SEX-LINKED
In sex linked characteristics the ___crosses
do not give the same results
reciprocal
For X-linked genes fathers do not pass the mutant
allele onto their ___
sons
For X-linked genes fathers pass the mutant allele
onto their daughters who are ___
carriers
Carrier mothers may pass the allele onto their sons with a chance of ___
50%
- Females showing the trait for an X-linked mutant
allele can exist but they are ___
rare
Female carriers may show patches of cells with
either trait due to ___
X chromosome inactivation
example of sex-linked traits and disorders
Male pattern baldness, red-green colour
blindness, myopia, night blindness,
hemophilia
Color blindness is found mostly in
males
- complete color blindness, seeing
only shades of gray
achromatopsia
difficulty telling the difference
between red/purple and green/purple
deuteranopia
– Deuteranopia - difficulty telling the difference
between
red/purple and green/purple
difficulty telling the difference
between blue/green and red/green
protanopia
– Protanopia - difficulty telling the difference
between
blue/green
red/green
difficulty telling the difference
between yellow/green and blue/green)
tritanopia
Tritanopia - difficulty telling the difference
between
yellow/green
blue/green
= Red-Green
Colourblindness
daltonism
daltonism is ___colorblindness
red/green
two types of photoreceptor
cones
rods
photoreceptor with a max sensitivity of 505nm
rods
photoreceptor that has red, green, and blue sensitive
cones
cone
___ sensitive 560nm
red
cone
___ sensitive 530nm
green
cone
___ sensitive 420nm
blue
rod
max sensitivity ____
505nm
its distribution is Concentrated in the fovea
color photoreception
is a small pit in the retina that provides sharp, central vision.
fovea
Widely spread over whole
retina, absent from fovea
monochrome photoreception
3 proteins controlled by 3 genes
color photoreception
which pigments in color photoreception are sex linked
red
green
which pigment in photoreception is autosomal
blue
pigment for monochrome photoreception
rhodopsion
rhodopsin is composed of (2)
retinol (vit a)
opsin (protein)
rhodopsin is also called
visual purple
bleaching of color photoreception is
slow
bleaching of monochrome photoreceptioin is
fast (very sensitive)
regeneration of color photoreception
slow (after images in bright light, complementary colors)
regeneration of monochrome photoreception
fast
use of color photoreception
Daylight vision
Light adaptation 5 min
use of monochrome photoreception
Night vision
Dark adaptation 20 min or
wear red goggles!
Hemophilia is a recessive X-linked
trait. What is the probability of a
couple having a hemophiliac child if
the man does not have hemophilia
and the woman is a carrier?
Hemophilia is indeed a recessive X-linked trait, meaning the gene responsible for hemophilia is located on the X chromosome. Men have one X and one Y chromosome (XY), while women have two X chromosomes (XX).
In this scenario:
The man does not have hemophilia (XᵐY), where Xᵐ is a normal X chromosome.
The woman is a carrier (XʰXᵐ), where Xʰ carries the hemophilia gene.
Let’s consider the possible combinations for their children:
The possible combinations for daughters are:
XʰXᵐ (carrier, like the mother)
XᵐXᵐ (normal, not a carrier)
The possible combinations for sons are:
XʰY (affected by hemophilia)
XᵐY (normal, like the father)
Since each child inherits one X chromosome from the mother and one sex chromosome from the father (either X or Y), the probabilities are as follows:
50% of their daughters will be carriers (XʰXᵐ).
50% of their daughters will be normal (XᵐXᵐ).
50% of their sons will have hemophilia (XʰY).
50% of their sons will be normal (XᵐY).
Given these combinations, the overall probability of the couple having a child with hemophilia is 25%. This is because 50% of their sons have a 50% chance of having hemophilia, and sons make up half of their potential offspring.
hese exposed fibers activate a series of proteins in the blood called
clotting factors
One of these clotting factors eventually converts a protein called prothrombin into its active form
thrombin
Thrombin then converts another protein, fibrinogen, into
fibrin
This involves a deficiency in Factor VIII
what type of hemophilia
hemophilia A
This involves a deficiency in Factor IX (antihemophilic factor B)
hemophilia B
The blood clotting reaction is an ___ involving Factors XII, XI, IX, X and II
enzyme cascade
The blood clotting reaction is an enzyme
cascade involving Factors
XII
XI
IX
X
II
Other factors including proteins like Factor __
are essential as coenzymes.
VIII
- About 85% of hemophiliacs suffer from ___
classic hemophilia
They cannot produce factor VIII
classic hemophilia
The rest show ___disease where they
cannot make factor IX
christmas
The rest show Christmas disease where they
cannot make factor __
IX
Hemophiliacs do clot their blood slowly because
there is an alternative pathway via
thromboplastin
is a genetic
family tree that shows
how prevalent a trait is
in a family unit from
generation to
generation.
pedigree
They are often used to
track the expression of
genetic conditions and
disorders
pedigree
___ represent males
and ___females
squares
circles
A ___in shape
means that person has the
trait in question
coloured
A ____ in shape
means that they are
carrying an allele for a
recessive trait.
half coloured
Refers to those situations in which a single
copy of an allele is sufficient to cause
expression of a trait
autosomal dominant inheritance
means not on the sex
chromosomes
autosomal
- Every affected person should have at least one
affected parent.
* 2. Males and females should be equally often
affected.
* 3. An affected person has at least a 50% chance
of transmitting the dominant allele to each
offspring.
autosomal dominant inheritance
(caused by a mutation) in which the
person ages very rapidly. They die before they can
reproduce.
progeria
Autosomal Dominant Inheritance
Examples
progeria
huntington’s disease
e in which the central nervous
system starts to break down around the age of 30.
huntinton’s disease
Refers to those situations where two
recessive alleles result in a trait being
expressed.
autosomal recessive inheritance
- An affected person may not have affected parents. Parents
would be carriers.
* 2. Affects both sexes equally. Can appear to skip generations.
* 3. Two affected parents will have affected children 100% of the time.
autosomal recessive inheritance
Autosomal Recessive
Examples
albinism
tay sachs
is a genetic condition which is the loss
of pigment in hair, skin and eyes
albinism
is a genetic disorder which is a build
up of fatty deposits in the brain, eventually
proving to be fatal.
Tay Sachs
- Refers to those situations where a recessive
allele on the X chromosome can lead to a
trait/condition or disorder
x-linked recessive inheritance
Males are affected more often than females. Ratio of ___ in x-linked recessive inheritance
8:1
Affected males will transmit the allele to all
___, but not to sons.
x-linked recessive inheritance
daughters
can arise only from
matings in which the father is affected and the
mother is affected or a carrier.
homozygous recessive females
which
causes progressive and degenerative
muscle weakness
duchenne muscular dystrophy
x-linked recessive disorders include
hemophilia
duchenne muscular dystrophy
given that the gametes are
XC
Xc
Y
where
Xc = colorblind gene
give the GR and PR
GR: 1XCXc:1XCY
PR: 1 normal female (but carrier): 1 normal male
Refers to situations where a single dominant
allele on the X chromosome can lead to a
trait/condition
x-linked dominant inheritance
- Twice as many females are affected as males.
* 2. Usually half the children of an affected female will be
affected, regardless of sex.
* 3. All the daughters of an affected male will be affected but
none of the sons.
x-linked dominant inheritance
example of x-linked dominant
vitamin D resistant rickets
which can
lead to bone deformities, particularly in
the lower limbs (bowed legs)
vitamin D resistant rickets
XDXD - female with defective teeth enamel
XDXd - female with defective teeth enamel
XdXd - female with normal teeth
XD – male with defective teeth enamel
XdY - male with normal teeth
defective teeth x normal teeth
XDXD x XdY
give GR and PR
1 XDxd
1 XDY
PR: 1 daughter with defective teeth
1 son with defective teeth
Chart showing genetic relationships between members
of a family
pedigrees
produces bone disorders such as rickets that cannot be cured with vitamin D
hypophosphatemia
hypophosphatemia is an example of X-linked ___
dominant
characterized by browning of teeth
defective teeth enamel
defective teeth enamel is an example of X-linked ___
dominant
atrophy of adrenal glans, mental deterioration, death 1-5 years after onset
adrenuloeukodystrophy
adrenoleukodystrophy is an example of X-linked ___
recessive
insensitive to green light; 60-75 percent of color blindness
deutan colorblindness
deutan colorblindness is an example of X-linked ___
recessive
insensitivity to red light; 25-40 percent of colorblindness
protan colorblindness
protan colorblindess is an example of X-linked ___
recessive
metabolic disease caused by lack of enzyme a-galactosidase A; progressive cardiac, renal problems, early death
farby’s death
farby’s death is an example of X-linked ___
recessive
benign condition that can produce severe even fatal anemia in presence of certain foods and drugs
glucose-6-phosphate dehydrogenase deficiency
g6p dehydrogenase deficiency is an example of X-linked ___
recessive
inability to form blood clots; caused by a lack of clotting factor VIII
hemophilia A
christmas disease clotting defect caused by lack of factor IX
hemophilia B
hemophilia is an example of X-linked ___
recessive
skin disorder causing large, dark scales on extremities, trunk
Icthyosis
icthyosis is an example of X-linked ___
recessive
metabolic defect caused by lack of enzyme hypoxanthine guanine phosphoribosyl transferase (HGPRT); causes mental, self mutilation, early death
Lesch-Nyhan Syndrome
Lesch-Nyhan Snydrome is is an example of X-linked ___
recessive
duchenne-type, progressive; fatal condition accompanied by muscle wasting
muscular dystrophy
muscular dystrophy
insensitivity to testosteron in XY individual resulting in female sexual phenotyp
testicular feminization
whole body except palms, soles, head, and face is covered with rough bristly scales and cylindrical bristle-like outhrowths nearly an inch long
porcupine man
characterized by a web like connection between second and third toes
webbed toes
a conspicuous growth of hair on the outer rim of the ears
hypertrichosis of the ears
A carrier female (XCXc) marries a
normal male (XCY). What would be the
chance of colorblindness appearing in
their progenies?
Probability:
25% Normal female
25% Carrier female
25% Normal male
25% Colorblind male
So, there’s a 25% chance that any male child will be colorblind, while no female child will exhibit colorblindness due to this genetic combination
