Download Ch 6 PP

Matters of Sex




1. A trait that is __________________, will be found
mostly in males while ___________________ traits will
be spread out evenly between males and females.
2. _________________ are the tips of the
chromosomes – only about 5% of the entire
chromosome.
3. The blood-clotting disorder, __________________,
is a ____________ trait since its found mostly in
males.
4. The nucleus of a cell in a female, during
interphase, has one dark-staining X chromosome
called a _____________________________.


Family trees
Pedigree
◦ a graphic representation of genetic inheritance thru a
family.


Looks similar to a family tree
Uses symbols
◦
◦
◦
◦
Male
Female
Children
relationships









Family history of traits recorded over generations
Can tell if the trait is dominant
Recessive
Sex-linked
Autosomal
Circles –females
Squares –males
Marriage horizontal lines
Vertical lines children






Sex-linked vs autosomal
Only seen in males ---sex linked
Both sexes equally---autosomal
Dominant vs recessive
Trait is dominant then every infected individual’s
parent will have the disease
Recessive—parents are normal children are infected



Use pedigrees
Genetic counseling
Prenatal testing
◦ Amniocentesis/chorionic villi sampling to determine
karyotypes

ON THE FOLLOWING SLIDE, BE SURE TO LABEL:
◦ 1. Dominant or Recessive
◦ 2. Sex-linked or Autosomal

ON THE FOLLOWING SLIDES, BE SURE TO LABEL:
◦ 1. Dominant or Recessive
◦ 2. Sex-linked or Autosomal
◦ 3. Tell the genotype of each person

Ben and Jan are married with 4 boys. Ben has
dimples as does his 2 oldest boys. Jan’s parents
do not have dimples. Their youngest son married
a female with dimples and together they have 2
daughters and a son – all of who have dimples 
1. Does a dominant or recessive allele produce
the trait? Explain.
2. Is it autosomal or sex-linked? Explain.
3. What are the genotypes of all the individuals in
the pedigree? (Write them on the pedigree.)
4. What is the genotype of individual IV2? Explain.
5. What is the genotype of individual IV6? Explain.
6. What is the genotype of individual I1? Explain
Offspring must have 2 traits before the disorder will
show up – must be passed down from both parents
 If the parents’ do not show signs of the disorder,
they are considered to be CARRIERS
 This is why blood relatives should not have
children together – no incest!!!!
Consanguinity: “shared blood”—family members may
share certain traits or disorders





1. males and females are equally affected
2. Affected males and females can transmit the
gene, unless it causes death before reproductive
age
3. The trait can SKIP generations
4. Parents of an affected child are heterozygous or
carriers
CANCER
 Ex:
Tay-Sachs—problem with
chromosome 15
◦ Recessive disorder of the central nervous
system
◦ An enzyme that breaks down lipid
produced and stored under tissues is not
made and this lipid accumulates in the
cells
◦ Survival rate: 4-5 years
◦ Occurs in many Jews

Infants with Tay-Sachs disease appear to develop
normally for the first few months of life. Then, as nerve
cells become distended with fatty material, a relentless
deterioration of mental and physical abilities occurs.
The child becomes blind, deaf, and unable to swallow.
Muscles begin to atrophy and paralysis sets in. A much
rarer form of the disorder which occurs in patients in
their twenties and early thirties is characterized by
unsteadiness of gait and progressive neurological
deterioration. Patients with Tay-Sachs have a "cherryred" spot in the back of their eyes. The condition is
caused by insufficient activity of an enzyme called
hexosaminidase A that catalyzes the biodegradation of
acidic fatty materials known as gangliosides.




Ex: Phenylketonuria (PKU)
Recessive disorder that results from the absence of
an enzyme that converts one amino acid,
phenylalanine to a different amino acid tyrosine
Affects the CNS
Common among Nordic or Swedish people





Normal at first
Then the baby begins to drink milk which has high
amounts of phenylalanine
Mental retardation occurs
Special diets until brain is fully developed
Chromosome 12

One gene from either parent and the child is
affected
◦ Tongue rolling
◦ Hapsburg lip
◦ Free earlobes
◦ Hitchhiker’s thumb
◦ Almond shaped eyes
◦ Thick lips
◦ Hair in the middle section of your fingers

Ex: Huntington’s Disease
◦
◦
◦
◦
Lethal genetic disorder— AUTOSOMAL DOMINANT
Breakdown of certain areas of the brain
No treatment
Onset is between 30 and 50
◦ +++++++++++++++++++++++++++++++++++



Found on the X chromosome
Females: XX – 2 copies
Males: XY – 1 copy

Ex: colorblindness: Females XcXc
Males XcY

Others: hemophilia and male-pattern baldness


Ex: Rett Syndrome
◦ This type is rarely found in males because many types are
fatal or cause them to die before the reproductive age
◦ EX: Fragile X Syndrome
Brain disorder – causes the “forgetting” of things previously learned
-- very similar symptoms to Autism
--only found in female – WHY?
Missing piece of X chromosome
Mental retardation, large ears, elongated face
***************************************



1. Explain why DOMINANT, x-linked disorders are
more commonly found in females.
2. __________________ is a disorder with
chromosome 15 that prevents the body from
producing an enzyme needed to break down lipids
around nerves of the CNS.
3.___________________ means “shared blood” and is
shown by the symbols:____________________-

Homozygous Red Snap Dragons x Homozygous
White Snap Dragons
◦ Pink Snap Dragon
◦ RR x R’R’
◦ Neither allele is completely dominant over the other
one
◦ R—protein to make red pigment
◦ R’—makes no pigment
◦ Pinkish color
◦ Does have segregation of alleles
◦ What happens in the F2 generation?

Mendelian Genetics
◦ Simple---dominant or recessive alleles
◦ NOT ALWAYS THIS SIMPLE!!!!!!






Both phenotypes appears
Chickens
Black-feathered and white-feathered birds both
homozygous
BB x WW
Produces a chicken with black and white feathers—
checkered
++++++++++++++++++++++++++++



1. If both parents carry the recessive allele that
causes cystic fibrosis (autosomal recessive trait),
whats the % chance that their child will have it?
2. PKU is a recessive disorder that results from the
absence of an enzyme that turns _________________
into tyrosine.
3. Tay-sachs occurs mainly in ____________.





Autosomes
Chromosomes that are not involved with
determining sex
1-22 pairs
Sex chromosomes
X and y chromosomes that determine the sex of
individuals




Traits that are found on the x and y chromsomes
X and y are not homologous
Found by Thomas Hunt Morgan
Used flies and noticed that the male had white eyes;
crossed red x white and got red; did not get the 3:1
ratio because only males had white eyes



Color blindness
Male pattern baldness
hemophilia


Traits that are controlled by 2 or more alleles
Pigeon feathers
◦ Ash-red
◦ Wild type blue feathers
◦ Chocolate feather

Blood types – A and B are codominant, O is
recessive.




Is the inheritance pattern of a trait that is controlled
by two or more genes
Genes maybe on the same chromosome or on
different chromosomes
When a trait is produced by main gene interactions
Ex: Skin color:




Dominant genes A,B,&C – control dark pigmentation
Recessive genes a,b,&c – has lowest amount of pigmentation
EX: AaBbCc would be what skin color?________________
++++++++++++++++++++++++++++++++++++++



External Environment
Temperature, nutrition, light, chemicals, and
infectious agents all can influence gene expression
What can TEMP do to proteins? (hormones for
example, insulin, ect)


Internal environment
Hormones and structural differences between sex
◦ Male-pattern baldness
◦ hemophilia


1. Cri du chat
2. Progeria diseases

Symptoms
The syndrome gets its name ("cat's cry") from the
characteristic cry of infants born with the disorder.
The infant sounds just like a mewing kitten, due to
problems with the larynx and nervous system. This
cry identifies the syndrome. About 1/3 of children
lose the cry by age 2. Other symptoms of cri-duchat syndrome may include:






Feeding problems because of difficulty
swallowing and sucking
Low birth weight and poor growth
Severe cognitive, speech, and motor delays
Behavior problems such as hyperactivity,
aggression, tantrums, and repetitive movements
Unusual facial features which may change over
time
Diagnosis is based on the distinctive cry and
accompanying physical problems. Genetic testing
(FISH) can confirm the diagnosis.

A deletion is caused by a break in the DNA molecule
that makes up a chromosome. In most cases, the
chromosome break occurs while the sperm or egg
cell (the male or female gamete) is developing.
When this gamete is fertilized, the child will develop
cri-du-chat syndrome. The parent, however, does
not have the break in any other cells of the body
and does not have the syndrome. In fact, the break
is usually such a rare event that it is very unlikely
that any other children will have this disorder.




At birth, a child with Hutchinson-Gilford progeria
appears normal. The syndrome begins to show
around 6-12 months of age, when the baby fails
to gain weight and skin changes occur. Over time,
the child begins to look like an elderly person.
Some of the characteristic symptoms are:
Head and face: baldness, prominent scalp veins
and eyes, small jaw, delayed tooth formation
Bones: thin limbs with prominent joints, short
stature, joint stiffness, hip dislocations
Heart disease and artery disease





Werner syndrome is a less well-known but more common
form of progeria, occurring in about 1 in 1 million
individuals. Typically, Werner syndrome is identified when
an adolescent fails to have a normal growth spurt. Over
time, the young person begins to look elderly. Some of
the characteristic symptoms are:
Striking difference between the person's appearance and
his/her real age
Head and face: gray hair and/or balding, wrinkling of the
face, cataracts, sunken cheeks and small jaw, a highpitched voice
Bones: osteoporosis, small stature, muscle weakness
Diabetes and cancer common

Since the pedigrees presented are simple
pedigrees, the following assumptions can be
made:
◦ No new mutations occur in the families. This means that
a dominant trait must occur in a parent if it appears in a
child. This also means that if a recessive trait appears in
a child but does not occur in either parent, both parents
must be heterozygous carriers for the trait.
◦ All traits are 100% penetrate. This means that if the
genotype for the trait occurs in an individual, the trail
will appear.

If neither parent is affected,
◦ the trait cannot be dominant.
◦ the trait could be recessive and either parent or both could
be heterozygous carriers.

If one parent is affected,
◦ the trait could be dominant and the affected parent could
be heterozygous while the unaffected parent is not a
carrier
◦ the trait could be recessive and the affected parent is
homozygous while the unaffected parent could be a
heterozygous carrier

If both parents are affected
◦ the trait could be dominant and both parents could be
heterozygous carriers which means that some of the
children could be unaffected
◦ the trait could be recessive meaning that both parents
would have to be homozygous and all the children would
have to be affected
Consideration of X-linked or Y-linked traits:

X-linked recessive
◦


affected male children must have, at least, an heterozygous
mother
an affected female will transmit the trait to all male children
X-linked dominant
◦


affected males transmit the trait to all daughters
affected sons must have an affected mother
Y-linkage
◦


male to male transmission only
no affected females

Mitochondria associated traits
◦ affected females transmit the trait to all children
◦ affected males do not transmit the trait to any children
Mitochondria contain their own DNA – but only the mother
can pass down mitochondrial DNA to her offspring


Females are homogametic – they have the same sex
chromosomes (XX)
Males are heterogametic – they have different sex
chromosomes (XY)
◦ Other species can be different:
 Ex: male snakes are ZZ and females are ZW
 The X chromosome carries 1500 genes, the Y
chromosome can only carry approx 230 (much smaller)
Telomeres: tips of the
chromosome
*Pseudoautosomal region:*
•The tips of the Y chromosome
that compromise 5% of the
entire chromosome
•They have counterparts on the
X chromosome and can cross
over with them



is the condition in which an organism is born with
secondary sex characteristics or a phenotype that is
different from what would be expected on the basis
of the gonadal tissue (ovary or testis).
In some cases, the external sex organs look
intermediate between the typical clitoris or penis.
In other cases, the external sex organs have an
appearance that does not look intermediate, but
rather has the appearance that would be expected
to be seen with the "opposite" gonadal tissue.



Because of this, pseudohermaphroditism is
sometimes not identified until puberty. It is
possible for the condition to be undetected until
adulthood.
The term "male pseudohermaphrodite" is used
when a testis is present
The term "female pseudohermaphrodite" is used
when an ovary is present.


The term "true" hermaphrodite is reserved for the
very RARE cases where both ovarian and testicular
tissue is present.
A person would be XY but look phenotypically like a
female




Very poorly understood – does NOT mean
transvestite
When an individual has the phenotype and sex
chromosomes of one gender, but feels strongly that
he or she is the “other” gender
Genetic of physical basis is not known
Many undergo surgery so their “physical” selves
match their gender




Very poorly understood – does NOT mean
transvestite
When an individual has the phenotype and sex
chromosomes of one gender, but feels strongly that
he or she is the “other” gender
Genetic of physical basis is not known
Many undergo surgery so their “physical” selves
match their gender


1. Y-linked: genes on the ______ chromosome
◦ Rare since the Y chromosome has very little genes
2. X-linked: genes on the ______chromosome
3. Females: traits on the X chromosome have to come in
______ copies to show up
4. Males: traits on the X chromosome only have to come
in _____ pair
5. The male is said to be _____________for X-linked traits
since they only need 1 copy
6. Explain the main difference between a hermaphrodite
and a person who is trasngender.

Females must have 2 copies

Males only have to have 1 copy

Common for an unaffected mother (carrier) to pass
it on to an affected son – even if the father is NOT a
carrier
Ichthyosis: an enzyme deficiency
blocks the removal of cholesterol
from skin cells – upper skin can’t
peel off causing a brown scaly
apperance

Ex: Hemophilia – blood cotting disorder
Ex: Color-blindess
Ex: male-patterned baldness

Most common in males, rare in females







Very rare
1. Females: get the illness, only has to have 1 copy
2. Males: more severely affected because there are
no other alleles to offset it
3. high rates of miscarriage due to early lethality in
males
4. passed from male to all daughters but to no
sons….WHY?__________________________________
Incontinentia Pigmenti: lesions
that look warty and eventually
turn into brown splotches that
remain for life
•Males don’t survive to be born

Pedigree Test Page