2. WHAT IS
GENETICS?????
The branch of biology that deals with
heredity, especially the mechanisms of
hereditary transmission and the
variation of inherited
characteristics among
similar or related
organisms
3. DNA
DNA, or deoxyribonucleic acid, is the hereditary
material in humans and almost all other
organisms. Nearly every cell in a person’s body
has the same DNA.
Most DNA is located in the cell nucleus (where it is
called nuclear DNA), but a small amount of DNA
can also be found in the mitochondria (where it is
called mitochondria DNA or mtDNA).
The information in DNA is stored as a code made
up of four chemical bases: adenine (A), guanine
(G), cytosine (C), and thymine (T).
4. DNA bases pair up with
each other, A with T and
C with G, to form units
called base pairs.
Each base is also
attached to a sugar
molecule and a
phosphate molecule.
Together, a base, sugar,
and phosphate are called
a nucleotide.
Nucleotides are arranged
in two long strands that
form a spiral called a
double helix.
5. NUCLEOTIDE: group of molecules that when linked
together, form the building blocks of DNA and RNA;
composed of phosphate group, the
bases:adenosine,cytosine,guanine and thymine and a pentose
sugar.In case of RNA,thymine base is replaced by uracil.
CODON: series of three adjacent bases in one polynucleotide
chain of a DNA or RNA molecule which codes for a specific
amino acid.
GENETIC CODE: the sequence of nucleotides in a DNA
or RNA molecule that determines the amino acid sequence in
the synthesis of proteins.
6. Chromosomes:
Chromatin: DNA, RNA &
proteins that make up
chromosme
Chromatids: one of the two
identical parts of the chromosome.
Centromere: the point where two
chromatids attach
The short arm of the chromosome
is labeled the “p arm.” The long
arm of the chromosome is labeled
the “q arm
7. How many chromosomes do
people have?
In humans, each cell
normally contains 23 pairs
of chromosomes, for a
total of 46.
Twenty-two of these pairs,
called autosomes, look the
same in both males and
females.
The 23rd pair, the sex
chromosomes, differ
between males and
females. Females have
two copies of the X
chromosome, while males
have one X and one Y
chromosome.
8. Gene
A gene is the basic physical and
functional unit of heredity.
Genes, which are made up of
DNA, act as instructions to make
molecules called proteins.
Every person has two copies of
each gene, one inherited from
each parent.
Most genes are the same in all
people, but a small number of
genes (less than 1 percent of the
total) are slightly different
10. ALLELS
Is one member of a pair or series of
different forms of a gene.
Homozygous-an organism in which 2
copies of genes are identical i.e. have same
alleles
Heterozygous-an organism which has
different alleles of the gene
11.
12. Congential Disease.
Diseases which are present at birth.
Hereditary/Familial Disease.
Diseases which are derived from one’s
parents and trasmitted in the gametes through the
generations.
Not all congenital diseases are genetic(
congenital Syphilis) and not all genetic
diseases are congenital (Huntington disease).
14. Mutation
it is defined as a permanent changes in the
DNA.
Mutation that affect germ cell are
transmitted to the progeny and can give rise
to inherited disease.
15. What kinds of gene mutations
are possible?
The DNA sequence of a gene can be altered in a
number of ways. Gene mutations have varying
effects on health, depending on where they
occur and whether they alter the function of
essential proteins. The types of mutations
include:
1. Missense mutation
2. Nonsense mutation
3. Insertion
4. Deletion
5. Duplication
6. Frameshift mutation
7. Repeat expansion
16. Missense mutation
This type of mutation is a change in one
DNA base pair that results in the
substitution of one amino acid for another in
the protein made by a gene
17. Nonsense mutation
A nonsense mutation is also a change in one DNA
base pair.
Instead of substituting one amino acid for another,
however, the altered DNA sequence prematurely
signals the cell to stop building a protein.
This type of mutation results in a shortened protein
that may function improperly or not at all.
18. Insertion
An insertion changes the number of DNA
bases in a gene by adding a piece of DNA. As
a result, the protein made by the gene may not
function properly.
19. Deletion
A deletion changes the number of DNA bases by
removing a piece of DNA.
Small deletions may remove one or a few base pairs
within a gene, while larger deletions can remove an
entire gene or several neighboring genes.
The deleted DNA may alter the function of the resulting
protein(s)
20. Duplication
A duplication consists
of a piece of DNA that
is abnormally copied
one or more times.
This type of mutation
may alter the function
of the resulting
protein.
21. Frameshift mutation
This type of mutation occurs when the addition or
loss of DNA bases changes a gene’s reading
frame.
A reading frame consists of groups of 3 bases that
each code for one amino acid.
A frameshift mutation shifts the grouping of these
bases and changes the code for amino acids.
The resulting protein is usually nonfunctional.
Insertions, deletions, and duplications can all be
frameshift mutations.
22. Repeat expansion
Nucleotide repeats are short DNA sequences that are repeated a
number of times in a row.
For example, a trinucleotide repeat is made up of 3-base-pair
sequences, and a tetranucleotide repeat is made up of 4-base-
pair sequences.
A repeat expansion is a mutation that increases the number of
times that the short DNA sequence is repeated.
This type of mutation can cause the resulting protein to function
improperly.
23. What happens in the
laboratory?
In a genetics laboratory, specific tests will be
performed depending on the reason the
patient has been referred.
The test may look for:
alterations in the sequence of bases in a
specific section of DNA (molecular genetic
tests)
alterations in large areas of DNA which may
encompass one or more genes
(cytomolecular genetic tests)
alterations which may affect the number or
structure of chromosomes (cytogenetic tests)
24. Karyotyping
Karyotyping is a laboratory technique used to
analyze chromosomes in order to look for any
major chromosomal anomaly which may cause a
genetic condition.
A karyotype is a photographic representation of a
stained metaphase spread in which the
chromosomes are arranged in order of
decreasing length.
The analysis can be carried out on a sample of
blood, chorionic villi or other material containing
cells .
With the help of Karyotyping the number of
chromosomes, their arrangement, size and
structure can be analysed.
25. How does karyotyping work?
A variety of techniques is used for
staining of chromosomes and the
most commonly used technique is
Giemsa stain (G banding), each
chromosomes set can be seen to
posses a distinctive pattern of
alternating light and dark bands of
variable widths which helps in
detection and localization of each
chromosomes and structural
abnormalities.
26. Numeric Abnormalities
These are usually caused by a failure of
chromosome division, which results in cells
with an extra chromosome or a deficiency
in chromosomes.
In human normal chromosomes count is
46 i.e. 2n = 46
An exact multiple of the haploid number (n)
is called euploid.
Chromosomes no such as 3n or 4n are
called polyploid
Any no that is not exact multiple of n is
called aneuploid.
27. Gametes with numeric anomalies can result in conditions such as Down
syndrome (who have 47 chromosomes instead of 46), or Turner syndrome
(45 chromosomes).
Common types of numerical aberrations are: triploidy, trisomy, monosomy
and mosaicism
Karyotype of Turner syndrome (45
chromosomes instead of 46)
Karyotype of Down Syndrome (47
chromosomes instead of 46)
28. Structural Abnormalities:
Structural changes usually designed using a cytogenic
shorthand in which p( french, petit) denotes the short arm of
chromosomes and q, the long arm.
Each arm is then divided into numbered region (1,2,3 and so
on) from centromere outward and within each region the
bands are numerically ordrered.
Thus 2q34, indicates chromosomes 2 long arm, region 3,
band 4.
The paterens of chromosomal rearrangements after breakage
are as follows.
Translocations: A portion of one chromosome is transferred
to another chromosome. There are two main types of
translocation.
In a reciprocal translocation, segments from two different
chromosomes have been exchanged. In genetic shorthand,
they are indicated by t followed by the involved chromosomes
in numeric order. i.e. 46XX,t(2;5)(q31;p14) indicate
translocation involving the long arm (q) of chromosome 2 at
region 3 band 1 and the short arm of chromosoes 5, region
1,band 4.
29.
30. Deletions: A portion of the chromosome is
missing or deleted.
Duplications: A portion of the chromosome
is duplicated, resulting in extra genetic
material.
Inversions: A portion of the chromosome has
broken off, turned upside down, and
reattached. As a result, the genetic material is
inverted.
Rings: A portion of a chromosome has
broken off and formed a circle or ring. This
can happen with or without loss of genetic
material.
31. Most chromosome abnormalities occur
as an accident in the egg or sperm. In
these cases, the abnormality is present
in every cell of the body. Some
abnormalities, however, happen after
conception; then some cells have the
abnormality and some do not.
Chromosome abnormalities can be
inherited from a parent (such as a
translocation) or be "de novo" (new to
the individual). This is why, when a child
is found to have an abnormality,
chromosome studies are often
performed on the parents.
