Download Genetics

Genetics
U.K. College of
Nursing
Genes and
Chromosomes
Each cell contains 23 pairs of
matched chromosomes for a
total of 46 chromosomes per
cell.
One chromosome from each
pair is inherited from each
parent.
There are 22 pairs of
autosomes, which control most
traits in the body, and one pair
of sex chromosomes, which
determine gender and other
traits.
Genes and
Chromosomes
Some genes are dominant and
their characteristics are
expressed even if only on one
chromosome.
Some genes are recessive and
their characteristics will be
expressed only if they are
carried by both chromosomes
in a pair.
Group Exercise
Human Variation
Punnet Squares
Visual representation of the
principles of inheritance
Dominant trait--Capital letter
Recessive trait--Small letter
Male vs female trait/gene
Patterns of
Inheritance
Autosomal Dominant
Autosomal Recessive
Sex-Linked (or X-linked)
Dominant
Sex-Linked (or X-linked)
Recessive
Chromosomal Abnormalities
Congenital Anomalies
Autosomal
Dominant
Trait appears in every
generation (does not skip)
Both males and females are
affected
Each pregnancy of an affected
person has a 50% chance of
producing an affected
offspring
Autosomal
Dominant Disorders
Disorders
Huntington’s Disease
Retinitis Pigmentosa
Polycystic Kidney Disease
Achodroplasia
Marfan Syndrome
Dominant
Disorders- Marfan
Syndrome
Autosomal Dominant Inheritance
Autosomal
Dominant
Clinical Situation-One parent is unaffected
One parent carries the defective
gene for Marfan Syndrome
Draw the Punnet Square
Autosomal
Dominant Punnett
Square
Autosomal
Recessive
Both parents are usually
unaffected, but are carriers
Trait first appears only in
siblings rather than in parents
 Trait found equally in males
and females
25% risk when both parents
are carriers
Increased incidence with
consanguinity
Autosomal
Recessive
Disorders
Phenylketonuria
Fanconi’s Anemia
Tay Sachs Disease
Sickle Cell Anemia
Cystic Fibrosis
Autosomal Recessive Inheritance
Autosomal
Recessive
Clinical Situation
Male carries the defective gene
for Tay Sachs disease
Female carries the defective
gene for Tay Sachs disease
Draw the Punnett Square
Autosomal
Recessive Punnett
Square
X-linked Inheritance
Sex-Modified Traits - Dominant
genes are expressed in both
males & females but at
differing frequencies
Ex: Baldness - expressed as
dominant in males, but recessive
in females, never as severe in
females
X-linked Dominant
Very rare
Often lethal in males therefore
few males present in the
pedigree
Multiple miscarriages may be
present
No carrier status, all
individuals with the gene are
affected
Trait appears in every
generation
X-linked Dominant
Female children of affected males
will all be affected (100% risk); no
male to male transmission.
Homozygous females (both X
chromosomes are affected) have a
100% chance of having an affected
child of either sex.
Heterozygous females (only one X
affected) have a 50% of having an
affected child with each pregnancy.
X-linked Dominant
Disorders
Hypophosphatemic Rickets
Fragile X Syndrome
Fragile X Syndrome
X-linked Dominant
Clinical Situation
Male is affected with
hypophosphatemic rickets
Female is unaffected
Draw the Punnet square
X-linked Dominant
Punnet Square
X-linked Recessive
Incidence of trait much higher
among males in a kinship than
among females
Trait cannot be transmitted from
father to son
An affected male will pass the
carrier status to all his daughters
Female carriers have a 50% risk of
transmitting the gene to their
offspring with each pregnancy
X-linked Recessive
Disorders
Hemophilia A
Duchenne’s Muscular Dystrophy
Color-Blindness
Duscenne’s
Muscular Dystrophy
X-Linked Recessive Inheritance
X-linked Recessive
Clinical Situation
Male is affected with Hemophilia
A
Female is normal (non-carrier)
Draw the Punnett Square
Use X1 for chomosome with
normal allele and X2 for
chromosome with disease
allele
X-linked Recessive
Punnet Square
X-linked Recessive
Clinical Situation
Male is normal
Female is a carrier of colorblindness
Draw the Punnett Square
X-linked Recessive
Punnett Square
X-linked Recessive
Clinical Situation
Male is affected with Duschenne
Muscular Dystrophy
Female is carrier of Duschenne
Muscular Dystrophy
Draw the Punnett Square
X-linked Recessive
Punnett Square
Genotype - The actual gene
constitution of a given person.
Phenotype - The observable
characteristics of a given
person
Traits can be environmentally
modified
type 2 diabetes
PKU
Traits can be medically modified
Sickle cell disease (bone marrow
transplant)
Polycysitc kidney disease (kidney
transplant)
However, genotype stays the same
so next generation are not saved
from condition
Group Exercise
Punnet Squares and
Patterns of
Inheritance
Karyotypes
The arranged
representation of the
chromosomal make-up
of a cell nucleus
Chromosomal
Abnormalities
Abnormalities in number of
chromosomes
Caused by nondisjunction:
failure of homologous
chromosomes or sister
chromatids to separate
properly into different
progeny cells
Monosomy - condition in which
one chromosome of a pair is
missing from a somatic cell
Monosomy X Turners Syndrome
Monosomy--Turner’s Syndrome
Chromosomal
Abnormalities
Trisomy - condition in which
one chromosome in the pair is
pesent in three copies in a
somatic cell
Down Syndrome (21), Trisomy
13 or 18
Klinefelter’s Syndrome - XXY
Abnormalities of Chromosome Number
Trisomy
Chromosomal
Structural
Abnormalities
Deletions - absence of normal
chromosomal material; can be
terminal or interstitial
Duplications - presence of an
extra copy of a chromosomal
segment
Inversions - Intrachromosomal
re-arrangement such that the
rearranged section is inverted
Ring Chromosome - Fusion of
the ends of a chromosome
that forms a circle or ring
Chromosomal
Structural
Abnormalities
Translocations Interchromosomal
rearrangement; can be
balanced (all chromosomal
material is present) or
unbalanced (chromosomal
material has been gained or
lost); can be reciprocal or
Robertsonian
Structural
Abnormalities
Group Exercise
Karyotype CD-Rom
Congenital
Anomalies
Structural abnormalities
present at birth
Are usually not identified with
a known genetic cause
Cause may be a combination
of genetic and environmental
factors
Children at Risk for
Congenital
Anomalies
Positive family history of
structual anomalies
Child with one known
structural anomaly
The IUGR infant
The mentally retarded child
The unusual appearing child
Maternal Risk
Factors
Diabetes
Phenylketonuria (PKU)
Seizure disorder
Alcohol and substance abuse
Recurrent pregnancy loss
Teratogens
Environmental substances or
exposures that result in
functional or structural
disability.
Any agent which when given
to or ingested by a pregnant
woman can produce a
permanent morphologic or
functional abnormality.
Agents Which
Cause
Teratogenesis
Drugs and Chemicals; Alcohol
Infections (viruses, TORCH)
Radiation exposure
Fat-Soluble Vitamins
Nicotine
Heat
Fetal Susceptibility
to Teratogens
Gestational age at the time of
exposure
Drug dosage
Route of administration of
agent
Genetic predisposition of fetus
to respond to a particular
agent
Gestational
Susceptibility
Factors
 Days 1-17
Little effect
 Days 18-60
Period of organogenesis
Extreme sensitivity to major structural
abnormalities
 Days 61-270
Considerably reduced risks
Functional abnormalities can still
occur
Pedigrees
A pictorial representation or
diagram of the family history.
Allows visualization of
relationships of affected
individuals to other family
members.
May indicate a pattern of
inheritance
Helps pinpoint persons who
should be examined or tested.
Pedigree Format
3 generations AT LEAST!!
Note name of informant
Roman numerals for
generations
Number individuals on
pedigree across families
Pedigree Pointers
 Seek a balance between the need for
asking specific versus general questions.
 Ask specific questions about each
individual as you construct the pedigree
(birth defects, mental retardation,
specific traits relevant to the diagnosis or
concern)
 Ask general questions about the whole
family or section of a family. Can you
think of any family characteristics (traits)
or medical problems in more than one
family member?
Pedigree Reminders
Multiple reproductive
relationships
“Have you had
children/pregnancies by anyone
else?”
“Did you have any pregnancies
prior to this relationship?”
Don’t forget half-sibs,
abortions, miscarriages,
stillbirths, previous marriages.
Pedigree Pointers
Indicate possible relationships
“Sometimes when there is one
family member with cleft lip and
palate, there are others in the
family with little indentations in
their lower lip, heart problems at
birth, or poor vision and joint
pain. Can you think of anyone
in your family with anything like
that?”
Use words the clients will
understand
seizures = fits = fainting spells
Group Exercise
Final Group Work