Transcript human heredity 2013

Human Heredity
• polygenic trait - trait controlled by two or
more genes
• Pedigree - chart that shows the relationships
within a family
• Autosome - autosomal chromosome;
chromosome that is not a sex chromosome
• sex chromosome - one of two chromosomes
that determine an individual's sex; females
have two X chromosomes; males have one X
chromosome and one Y chromosome
Pedigree
- the family tree
- representation of the ancestry of
an individual’s family.
- symbolic representations of family
relationships and inheritance of a
trait
Pedigree Analysis
Parents
Offspring
Unaffected Male
Unaffected Female
Affected male
Affected female
A numbering system is
used to identify individuals
Individuals I1 and III1 express the
unusual trait being studied
Rest have normal phenotypes
Common Pedigree Symbols
Determining Sex Through Pedigrees
Determining Sex
• All egg cells carry a single X
chromosome (23X).
However, half of all sperm
cells carry an X
chromosome (23X) and
half carry a Y chromosome
(23Y). This ensures that
just about half of the
zygotes will be 46XX and
half will be 46XY.
Determining a Disorder through
Pedigrees
Determining a Disorder through
Pedigrees: Hemophilia
Polydactyly
Polydactyl
autosomal dominant inheritance
Ptolemy Dynasty 323
BC to 30 BC
The Ptolemaic dynasty, royal family which ruled the
Ptolemaic Empire in Egypt. Their rule lasted for 275 years,
from 305 BC to 30 BC. Ptolemy's family ruled Egypt until
the Roman conquest of 30 BC.
All the male rulers of the dynasty took the name Ptolemy.
Ptolemaic queens, some of whom were the sisters of their
husbands, were usually called Cleopatra, Arsinoe or
Berenice. The most famous member of the line was the last
queen, Cleopatra VII, known for her role in the Roman
political battles between Julius Caesar and Pompey, and
later between Octavian and Mark Antony. Her apparent
suicide at the conquest by Rome marked the end of
Ptolemaic rule in Egypt.
Techniques for
detecting human
genetic disorders
Karyotype - set of
photographs of
chromosomes
grouped in order
in pairs
Karyotype
• Making a
Karyotype
– Photograph
chromosomes
during mitosis
– Cut
chromosomes
out of
photograph
– Group them in
order, in pairs
– Male 46XY
– Female 46XX
Karyotype
• Ordered display of an individual’s
chromosomes.
• Collection of chromosomes from mitotic cells.
• Staining can reveal visible band patterns, gross
anomalies.
Meiosis KM
21
Meiosis KM
22
Meiosis KM
23
Meiosis KM
24
Ultrasound Picture At 12 Weeks
Week 34 Fetoscopy
Genetic disorders
http://learn.genetics.utah.edu/content/disorders/whataregd/
Library of genetic disorders:
Autosomal Disorders
• Genes for these disorders are located on autosomes
– Recessive disorder
– Dominant disorders
– Codominant disorders
• PKU stands for “phenylketonuria”.
It is one type of amino acid
disorder. People with PKU have
problems breaking down an
amino acid called phenylalanine
from the food they eat.
Tay-Sachs Disease
- autosomal recessive
disorder
- II1 and II2 must be
carriers
- at least 2 carriers in
generation I
- but all could be carriers
One wrong letter “Cracking the Code” PBS movie segment Tay sacs
http://www.pbs.org/wgbh/nova/body/cracking-the-code-of-life.html
Achondroplasia
Tay-Sachs Disease
Text Figure 4.4
Albinism
- Autosomal recessive
- Heterozygotes carry the recessive allele but
exhibit
the wildtype phenotype
Gene to Molecule
• In both cystic fibrosis and sickle cell disease, a
small change in the DNA of a single gene
affects the structure of a protein, causing a
serious genetic disorder.
• Phenolketoneuria - PKU is the actual lack of a
certain enzyme that breaks down the amino
acid phenylalanine.
Cystic Fibrosis
Chromosomal Disorders
• Nondisjunction error in meiosis in
which homologous
chromosomes fail
to separate
Down Syndrome
Technology
And
Genetic testing
Fetal testing
Carrier
Recognition
1.
Amniocentesis
2.
Chorionic villus
sampling (CVS)
3.
Ultrasound
4.
Fetoscopy
Newborn
screening
Nondisjunction
Junction place where things are
connected, homologous
chromosomes in meiosis I and sister
chromatids in meiosis II
Disjunction separation of junction
during anaphase I and anaphase II
Non-disjunction failure of
chromosomes to properly separate
during anaphase I and anaphase II
Nondisjunction results in
aneuploidy, or abnormal number of
copies of chromosomes
Down Syndrome
• Trisomy 21
– 47 chromosomes instead of 46
• United States, approximately 1 baby in 800 is
born with Down syndrome
• mild to severe mental retardation. It is also
characterized by an increased susceptibility to
many diseases
Down’s Syndrome Karyotype
trisomy 21
Down’s Syndrome Symptoms
• eyes often slant upwards and
outwards, and the back of the
head may be unusually flat.
• as high as 40% of Down's babies
will have some sort of congenital
heart defect
• will have some level of learning
disorder
• immune system which makes
them prone to infections,
particularly chest and sinus
infections.
• can have problems regulating
their temperature, and can have
very dry skin.
Patau’s karyotype
trisomy 13
Patau’s Syndrome Statistics
• Incidence of Patau syndrome is approximately 1
per 8,000-12,000 live births.
• Patau syndrome is the least common and the
most severe of the viable autosomal trisomies.
• Median survival is fewer than 3 days.
• First identified as a cytogenetic syndrome in 1960,
Patau syndrome is caused by an extra copy of
chromosome 13.
Cleft palate
Polydactyly
cyclopia (single
eye) with a
proboscis (the
projecting tissue
just above the
eye).
Edward’s Syndrome Statistics
• Prevalence is
approximately 1 in 60008000 live births.
• Trisomy 18 was
independently described
by Edwards et al and
Smith et al in 1960.
Among liveborn children,
trisomy 18 is the second
most common autosomal
trisomy after trisomy 21.
http://today.msnbc.msn.com/id/315234
63/ns/todayparenting_and_family/t/parentscelebrate-their-sons-life-all-days/
Republican presidential candidate Rick Santorum
Edward’s Syndrome
Trisomy 18
Edward’s Syndrome Symptoms
• Approximately 95% of conceptions with trisomy
18 die in embryonic or fetal life; 5-10% of
affected children survive beyond the first year.
• The high mortality rate is usually due to the
presence of cardiac and renal malformations,
feeding difficulties, sepsis, and apnea caused by
CNS defects.
• Severe psychomotor and growth retardation are
invariably present for those who survive beyond
infancy.
overlapping digits with
the second and fifth fingers
overriding the third and fourth
fingers respectively
Microglassia, microcephaly and
other head abnormalities
Sex-Chromosome Disorders
• Turner’s syndrome (X-)
– Women with Turner’s syndrome are sterile
because their sex organs do not develop at
puberty
Turner’s Syndrome Karyotype
monosomy 23
Turner’s Syndrome Symptoms
• Webbed neck
• Exhibit female
phenotype; sterile
• Short stature, high
arched palate
Klinefelter’s Syndrome Karyotype
Trisomy 23
Sex-Chromosome Disorders
• Klinefelter’s syndrome - Males (XXY; XXXY…)
– Unable to reproduce
– Large hips
– Lower testosterone
– Gynecomastia
Extra Y Statistics
• Most males have the 46-XY karyotype, but about 1 guy
in 1000 has two Y chromosomes, and is an XYY ("diploY", "diplo Y", "YY", "polysomy Y").
• XYY's average substantially taller, tend to be wiry-built,
and tend to have severe acne. Minor birth defects -like pectus, crooked eye, and minor outturning of the
elbows, are supposed to be common in XYY's.
• Now, XYY boys usually do have serious behavioral and
cognitive problems. The extra "Y" in an XYY is obviously
not silent (as is the extra "X" in a XXX woman). It seems
likely that the second "Y" adds a bit more
aggressiveness to a man's overall personality.
Extra Y Karyotype
trisomy/quadrasomy 23
Meta Female Statistics
•
•
With 3 X chromosomes (XXX), these females usually have no
apparent physical abnormalities except tallness and
menstrual irregularities
As adults, these individuals are usually an inch or so taller
than average with unusually long legs and slender
torsos. They have normal development of sexual
characteristics and are fertile. They may have slight learning
difficulties and are usually in the low range of normal
intelligence. They tend to be emotionally immature for their
size during childhood. None of these traits prevent them
from being socially accepted as ordinary women. This type of
chromosomal abnormality is apparently rare and little is
known about it. However, the frequency is approximately 1 in
1,000 female infants and it may be more common when the
mother is older. Metafemales are also called "triple-X
females."
Meta Female karyotype
Trisomy 23
Sex-Linked Genes
• Males have just one
X chromosome.
Thus, all X-linked
alleles are expressed
in males, even if they
are recessive.
Sex-Linked Disorders
• Colorblindness
• Hemophelia
• Duchenne Muscular Dystrophy
Other human
disorders
Cri-du-Chat Statistics
• The estimated incidence is about 1 in
50,000 livebirths
• In 1963, Lejeune et al described a
syndrome of multiple congenital
anomalies, mental retardation,
microcephaly, abnormal face, and a
mewing cry in infants
• Cri-du-chat syndrome is an
autosomal deletion syndrome caused
by a partial deletion of chromosome
5p. It is characterized by distinctive,
high-pitched, catlike cry in infancy
with growth failure, microcephaly,
facial abnormalities, and mental
retardation throughout life.
Cri-du-Chat Karyotype
Cri-du-chat Symptoms
• Approximately 75% of the patients
with cri-du-chat syndrome die within
the first few months of life and about
90% before they are aged 1 year. These
figures are from an older study (1978),
and decreased morbidity and mortality
are most likely with contemporary
interventions. Survival to adulthood is
possible.
• Pneumonia, aspiration pneumonia,
congenital heart defects, and
respiratory distress syndrome are the
most common causes of death.
Finding Cures Is Hard “Cracking the Code” PBS movie segment
57:00 – 1:05:00 maybe up to 1:13:00 if time permits
http://www.pbs.org/wgbh/nova/body/cracking-the-code-of-life.html
Contemplating the message “Cracking the Code” PBS movie segment
(1:39:00 – 1:44:00
Change it up
1:50:00 - 1:53:00)
The Future
http://www.pbs.org/wgbh/nova/body/cracking-the-code-of-life.html