• The study of heredity .
• Gregor Mendel- Austrian Monk -Father
of modern genetics
• Studied inheritance of characteristics
in green pea.
• The transmission of inherited
characters from one generation to
• Each characteristic is called a trait.
Are unit of heredity.
factor that control traits.
composed of DNA
Allele: a pair of genes located at the same
place on a homologous chromosome
• Dominant genes: those that mask the
presence of other corresponding genes
• Recessive genes: those whose physical
expression (phenotype) is masked in the
presence of a dominant gene.
• Phenotype: the physical appearance of a
plant or animal because of its genetic
• Genotype: genetic constitution (makeup)
of an individual
• Phenotype could be –Brown eyes .
• Genotype would be BB.
Types of genotype
• Heterozygous- when a plant or animal
has two genes for different traits
(example: tall and short)
• Homozygous- when a plant or animal has
two genes for the same trait (example:
two tall genes, or two short genes
• A chromosome is an organized structure
of DNA and protein found in cells.
• Contains 50% proteins and 50% DNA (deoxyribonucleic acid).
• Made of many chromatin threads
• Somatic cells contain 46 chromosomes, gametic
cells contain 23 chromosomes.
• 44 of our chromosomes are AUTOSOMES,
while 2 are called sex chromosomes.
• Each chromosome contains many GENES that
act as a blueprint or set of instructions for the
• The DNA in chromosomes forms the basis for the
• DNA is made of long chains of nucleotides.
• DNA has a DOUBLE-HELIX structure where 2
strands of nucleotides join and twist around to form a
spiral staircase or twisted ladder.
• Each nucleotide has 3 parts:
• 1. a phosphate group - helps form the backbone of
the DNA molecule
• 2. a sugar (deoxyribose) - acts as a glue,forms the
backbone with phosphate
• 3. nitrogen bases - 4 types (guanine, cytosine,
• Control of cell activities
• Undergo mutations
• The process of equal partitioning of
replicating chromosomes into identical
• Stages : interphase, prophase,
metaphase, anaphase, telophase and
Meiosis –reduction division
• Takes place in gamete or sex cells.
• There is double division maintaining the
DNA but reducing the chromosomal
count to 23.
• Meiosis I and Meiosis II
Law of Dominance
Law of Segregation
Law of Independent Assortment
LAW OF DOMINANCE
• Mendel’s first law of inheritance
• If two alleles are different i.e.
heterozygous ,the trait associated with
only one of these will be visible
(dominant) while the other will be
LAW OF SEGREGATION
The separation of allele into separate gametes
is law of segregation.
It states that every individual possesses a pair
of alleles (assuming diploidy) for any particular
trait and that each parent passes a randomly
selected copy (allele) of only one of these to
LAW OF ASSORTMENT
Also known as "Inheritance Law”
It states that separate genes for
separate traits are passed independently
of one another from parents to offspring
• Is an abnormal condition that a person
inherits through genes or chromosomes.
• Caused by mutations.
• Also known as Complex disorders.
• Associated with the effects of multiple
genes in combination with lifestyles and
Mendelian diseases are inherited according
to the Mendelian Laws.
Sex linked diseases
Individual with an autosomal dominant trait
will produce two kinds of gametes with
respect to the mutant gene.
Half with the mutant gene and half with
the normal allele.
Offspring of such individual has a 50:50
chances of being affected, provided the
other parent is normal.
• Abnormalities occur when both the
parents are heterozygous.
• Offspring of such parents has a chance of
1:4 being affected.
Sickle cell anemia
• A mutant gene on X chromosome in males
will express itself readily as there is no
• A mutant gene on X chromosome in
females will not express itself in the
presence of normal allele.
SEX LINKED DISEASES
• Incorrect number of chromosomes.
nondisjunction : chromosomes do not
separate properly. Eg trisomy monosomy
Breakage of chromosomes:
Examples of chromosomal
Down syndrome: trisomy 21
XXY :klinefelter syndrome male
XXX :trisomy female
XYY: Jacobs syndrome male
XO: Turner syndrome.
Also known as genetic susceptibility, genetic risk
Genetic predisposition is an inherited risk of developing a
disease or condition.
Having a genetic predisposition for a disease does not mean
that you will get that disease, but your risk may be higher than
that of the general population.
Genetic testing is able to identify individuals who are genetically
predisposed to certain health problems
Preventive and Social measures
Galton proposed the term eugenics
for the science, which aims to
improve the genetic endowment of
human population. Eugenics has
both negative and positive aspects.
The aim of negative eugenics is to
reduce the frequency of hereditary
disease and disability in the
community to the least possible
It seeks to improve the genetic
composition of the population by
encouraging the carriers of desirable
genotypes to assume the burden of
• (b) Euthenics
Studies with mentally retarded (mild)
children indicated that exposure to
environmental stimulation improved their
IQ. Thus the solution of improving the
human race does not lie in contrasting
heredity and environment, but rather in
mutual interaction of heredity and
environmental factors. This environmental
manipulation is called euthenics and has
considerable broader prospects for success
• (c) Genetic Counseling
The most immediate and practical service
that genetics can render in medicine and
surgery is genetic counseling.
Genetic Counseling may be
• Most genetic counseling is at present
retrospective i.e. the hereditary disorder has
already occurred with in the family
• The WHO recommends the establishment of
genetic counseling centres in sufficient
numbers in regions where infections disease
and nutritional disorders have been brought
under control and in areas where genetic
disorders have always constituted a serious
public health problem (i.e. sickle cell anaemia
• The methods which could be suggested under
retrospective genetic counseling are:
• Pregnancy termination
Sterilization depending upon the attitudes and
• Other genetic measures
Consanguineous marriages: When
blood relatives marry each other there
is an increased risk in the offspring of
traits controlled by recessive genes, and
those determined by polygenes.
Examples are : Albinism, Alkaptonuria,
Phenylketonuria and several others
Amniocentesis in early pregnancy
(about 14-16 weeks) has now made it
possible for prenatal diagnosis of
conditions associated with
chromosomal anomalies. EXAMPLE
Down’ s syndrome
Indications for pre-natal diagnosis
Advance maternal age
,previous child with
intrauterine growth delay
(amniocentesis , chorionic
Protein essay, DNA
Screening for neural tube
defects and trisomy
Maternal serum alphafoetoprotein and chorionic
Prevention Of Genetic Diseases: How
Genetic Testing Can Save Child's Life
• Genetic tests performed on newborns and
children can help parents prepare their
child for the possibility of developing a
hereditary disease. DNA tests can tell
parents many things about a child's genetic
makeup, including whether or not they
currently have a genetic disorder or
whether they are at risk for developing an
inherited disease later in life.
• Genetic testing often begins in the
womb. Doctors can administer prenatal
DNA tests to detect certain genetic
disorders, such as Down syndrome, as
well as numerous fatal birth defects.
• A technician uses a needle to
lightly prick your baby 's heel
and draw blood. This kind of
early attention to genetic
information can literally save
a child's life, as disease
prevention or treatment can
often begin immediately.
• Preventing genetic disorders once the child has been
born can be helped through newborn screening. This
typically involves taking a sample of blood from the
• Genetic testing is done in all hospitals to test for a
variety of metabolic disorders before symptoms
arise. These disorders can potentially lead to severe
mental retardation and even death.
• If a genetic disorder is detected, metabolic or
otherwise, treatment can begin immediately to
prevent complications and to ensure that your child
has the best possible chances for living a normal,
• A more thorough list of conditions looked for with
genetic testing and their possible preventative
measures can be found on the KidsHealth.org article
on newborn screening tests
• Recognizing Pre-clinical areas
Screening tests are available for the
Example- Heterozygotes for
phenylketonuria can be detected by a
phenylalanine tolerance test
Detection of Genetic carriers
Especially the inborn errors of
The female carriers of Duchenne type
of muscular dystrophy, an X- linked
disorder can now be detected by
elevated levels of serum creatine
kinase in 80 percent of carriers.
• Specific protection
Increasing attention is now being paid to the
protection of individuals and whole
communities against mutagens such as X-rays
and other ionizing radiations and also
Need of individualized and
specific education about how
Check regularly for the disease.
Follow a healthy diet.
Get regular exercise.
Avoid smoking tobacco and too
Get specific genetic testing that
can help with diagnosis and
• Disease prevention is an integral part of
parenthood, and prevention of genetic
disorders can help us take this one step
further to ensure that the child lives the
healthiest life possible.