GENETICS.pdf

HUMAN ANATOMY AND PHYSIOLOGY NOTES
RAMDAS BHAT
KARAVALI COLLEGE OF PHARMACY 1
CHAPTER NO:16
GENETICS

RAMDAS BHAT
• GENETICS is a branch of biology concerned with the study of genes, genetic variation,
and heredity in organisms.
• Gregor Mendel, a sci.e.,ntist and Augustinian friar, discovered genetics in the late 19th-
century.
• Mendel studi.e.,d "trait inheritance", patterns in the way traits are handed down from
parents to offspring.
• MENDEL named the gene as a factor.
• His works over the gene was not recognised
• Later in the early 19’s the sci.e.,ntist named JOHANSSEN named the factor that causes the
inheritance from the parents to the offspring as the GENE.
TERMS TO REMEMBER:
1. GENE: it is the basic unit of inheritance
2. ALLELES: They are the 2 forms of the gene; the alleles may be Dominant or recessive.
TALL(T)(DOMINANT) DWARF(t)(RECESSIVE)
3. HOMOZYGOUS: if the 2 gene is dominant or recessive i.e., TT, tt
4. HETEROZYGOUS: if one is dominant and other is recessive Tt.
5. PHENOTYPE: Physical appearance i.e., Tt(tall), TT(TALL) by the external appearance
one can say the plant is tall or dwarf(tt).
6. GENOTYPE: Genetical makeup
7. CROSS: crossing between the tall and a short.
8. FILLIAL: The next generation is formed by the crossing of the plants.
POLYGENIC INHERITANCE:
• They are also called as the quantitative inheritance mainly depending on the quantity of the
DOMINANT and RECESSIVE GENES.
• Skin colour is mainly dependent on the amount of the MELANIN.
• The amount of the melanin i.e., the skin colour is controlled by 3 genes i.e., A, B, C
• AABBCC here all the 6 genes are in the dominant form that means the amount of the
melanin in the individual is more. Colour of the skin is black
GENETICS

RAMDAS BHAT
• AaBbCc here 3 genes are dominant and 3 are recessive Melanin content will be
intermediate. Colour of the skin is Wheatish.
• aabbcc here all the genes are recessive and no melanin is produced they are called
ALBINOS.
• This type of inheritance is given by DAVIN PORT
• When AABBCC are crossed with aabbcc the childrens will have AaBbCc inheritance i.e.,
Intermediate inheritance
• When 2 intermediates are crossed the children will have ABC, ABc, AbC, aBC, Abc, aBc,
abC, abc. I.e., 8 different inheritances can be seen.
GENETIC DISSORDER:
SICKLE CELL ANEMIA:
• Described first by Herrick in 1910.
• The shape of the cell is Sickle.
• It is an AUTOSOMAL RECESSIVE
DISSORDER.
• The chances are equal in male and
female.
• The ß- chain of the Haemoglobin at
position 6, Glutamine is replaced by
Valine.
• I.e., On the DNA the orderly sequence
i.e., CTC during transcription to form m-RNA GAG that will code for Amino acid i.e.,
Glutamic acid but if the DNA has sequence CAC under transcription it will form GUG.
That codes for Valine. This is called POINT MUTATION.
• O2 holding capacity of the HB decreases and also cells become SICKLE.
PEDIGREE
• It is a recessive AUTOSOMAL DISSORDER.
• The normal gene is Given as HbA HbA for normal person
• The autosomal recessive gene for sickle cell anemia is given as HbA HbS
• The other sequence is HbS and HbS are highely recessive and these don’t survive upto
reproductive age and are ignored.

RAMDAS BHAT
HAEMOPHILIA:
• Also called as Royals disease or Bleeders disease (clotting time is delayed).
• They are of 2 types
1. Haemophilia A: Due to non-formation of clotting factor VIII.
2. Haemophilia B: Due to non-formation of clotting factor IX.
• It is a Sex linked Recessive genetic disorder and has a recessive gene
• The gene will be located on X chromosome and not on Y – chromosome.
• Hence the gene for the haemophilia is recessive and is located on the X chromosome.
PEDIGREE
• Normal man has crossed with a carrier mother having sex linked disease in one of the
chromosomes(X*)
• The childrens i.e., Male born will have a chromosome carrying a recessive gene (X*Y) and
a Y chromosome who are more affected whereas daughter will have a dominant(X-
NORMAL) and a recessive (X*) chromosome and are less affected due to presence of
Dominant chromosome.
• But if there is a crossing between a affected father(X*Y) with a affected carrier mother
(XX*), the childrens born will have a daughter affected (X*X*/ XX*) and the son born will
have (X*Y/XY)
• Only if the daughter has both the dominant and recessive gene that are affected will have
Haemophilia and not in other cases.

RAMDAS BHAT
MUTATION:
• Any sudden change occurring in hereditary material is called as mutation.
• They may be harmful, beneficial or neutral.
• DNA is highly stable molecule that replicates with amazing accuracy some errors of
replication do occur.
GENE MUTATION
• A gene mutation is defined as an alteration in the sequence of nucleotides in DNA.
• This change can affect a single nucleotide pair or larger gene segment of a chromosome.

RAMDAS BHAT
POINT MUTATION
• Point mutations are the most common type of gene mutation.
• Also known as base pair substitution.
• Change in a single nucleotide base pair.
• Point mutation can be categorized into three types:
1. Silent mutation
2. Missense mutation
3. Nonsense mutation
1. SILENT MUTATION:
• The change in one codon for an amino acid into another codon for that same amino acid
• Silent mutations are also referred to as synonymous mutations.
2. MISSENSE MUTATION
• The codon for one amino acid is changed into a codon for another amino acid.
• Missense mutations are sometimes referred to as non-synonymous mutations
3. NONSENSE MUTATION
• The codon for one amino acid is changed into a translation termination (stop) codon

RAMDAS BHAT
FRAME SHIFT MUTATIONS
• This type of mutation occurs when the addition or loss of DNA bases changes a gene' s
reading frame.
• A reading frame consists of 3 bases, each code for one amino acid.
• A frame shift mutation shifts the grouping of these bases and changes the code for amino
acids.
• The resulting protein is usually nonfunctional.
• Insertions and deletion can all be frame shift mutations.
INSERTION
• An insertion changes the number of DNA bases in a gene by adding a piece of DNA.
• As a result, the protein coded by the gene may not function properly.
DELETION
• A deletion changes the number of DNA bases by removing a piece of DNA.
• Small deletion may remove one or few base pairs within a gene.
• Larger deletions can remove one entire gene or several neighboring genes. The deleted
DNA may alter the function of the resulting protein.

RAMDAS BHAT
BASE SUBSTITUTION MUTATION
• Base substitution is mutation in which one base pair is replaced by another.
• Base substitutions can be divided into two subtypes:
1. Transition mutation
2. Transversion mutation
TRANSITION MUTATION
A transition is the replacement of a base by the other base of the same chemical.
TRANSVERSION MUTATION
A transversion is the opposite the replacement of a base of one chemical category by a base of
the other.

RAMDAS BHAT
CHROMOSOME:
• It is a DNA molecule with a part or
all of the genetic materials or a
genome of organism
• Visible under light microscopy
when the cells undergo the mitosis
i.e., metaphase
• Before the mitosis the chromosome
passes on to the synthesis phase of
the interphase where the
chromosome gets copied in this
phase and the sister chromatids are
formed that are attached to the
original chromosome by the
centromere.
• The placement of the centromere will be top middle or bottom of chromosome
• The ends of the chromosome is called as telomeres
• They are containing densely packed DNA molecules and protect the genetic material when
carried by chromosome.
• The locus/ loci form the fixed position on the chromosome where the genetic material are
present.
• The chromosomes will be in the highely condensed form in the metaphase stage and that
chromosome is called as the metaphasic chromosome.
• The chromosome is 0.2-20 µm in length
• They have 2 arms P arm (short arm) and a Q arm (long arm).
• There are 23 pairs of chromosomes out of which 22 pairs are called autosomes that
determines the genetic characters and 1 pair are called sex chromosomes that determines
the sex of the offspring.

RAMDAS BHAT
The chromosomes are of 4 types:
1. Metacentric chromosome
2. Submetacentric
3. Acrocentric
4. Telocentric (not in humans)
DNA:
• DNA also called as DEOXYRIBONUCLEIC ACID carries the genetic material or genetic
instructions incorrect time and in the correct sequence.
• DNA is used for the growth, development, functioning and reproduction of all living
organism and many viruses aswell.
• The model of DNA was explained by Watson and Crick i.e., a Double helical model.
• The structural feature of DNA is they are made of sugar and phosphate backbone which
are held together by a phosphodiester bond and in a helical shape by the bases
• The bases are PURINES DERIVATIVES i.e., ADENINE & GUANINE and
PYRIMIDINE DERIVATIVES ie THYMINE & CYTOSINE.

RAMDAS BHAT
• All these bases are arranged in a pair and these
are called base pairs.
• Always the purine is bonded with the
pyrimidine
• Adenine will bind to thymine with 2 hydrogen
bond and guanine with the cytosine with 3
hydrogen bonds forming a base pair of the
DNA this is called CHARGAFF’S RULE.
• Each base pair are attached
• Human DNA CONTAINS 3 BILLION
BASES and 99% of the people have same base
pairs.
• The structure of DNA is like a ladder and base
pairs forms the ladder Rungs, sugar phosphate
acts as sidepieces of the ladder
• DNA can replicate and forms the copy of its
own
• The double helical structure acts as a pattern
for duplication and this process happens in the
interphase stage of the Cell cycle.

RAMDAS BHAT
RNA:
• RiboNucleic acid is the abbreviation
• They are nucleic acid that carries the
information from the DNA into the
cytosol of the cell where they help in
the protein synthesis.
• They resemble as that of the DNA but
the difference in the Carbohydrate i.e.,
Ribose in place of and the nucleotide
pyrimidine Uracil in place of thymine.
• Here there is again the 3’-5’
phosphodiester bond.
Types of RNA
In all prokaryotic and eukaryotic
organisms, three main classes of RNA
molecules exist-
1) Messenger RNA(m RNA)
2) Transfer RNA (t RNA)
3) Ribosomal RNA (r RNA)
The other are –
1. Small nuclear RNA (SnRNA),
2. Micro RNA(mi RNA) and
3. Small interfering RNA(Si RNA) and
4. Heterogeneous nuclear RNA (hnRNA).
mRNA (MESSENGER RNA):
• They are messenger RNA
• Comprises of 5% of the total RNA
• They act as a messenger in carrying the information from the gene to the protein synthesis.
• It has 2 end 5’-prime end and 3’-prime ends.
• At 5’-prime end it has a cap that prevents the degradation of this end by exonuclease and
also help in recognition of mRNA by the translation mechanism.
• At 3’-primer end it has a poly adenosine (PolyA tail) prevent this end from exonuclease.

RAMDAS BHAT
t-RNA (TRANSFER RNA)
• It is smallest of all the species of RNA
• They have 74-95 amino acid residue.
• They transfer the amino acid from
cytoplasm to protein synthesis
machinery
• They are easily soluble hence the name
soluble RNA or s RNA
• The structure of tRNA is explained by
clover leaf model.
• All t-RNA contain 5 main arms or
loops which are as follows
a) Acceptor arm
b) Anticodon arm
c) D HU arm
d) TΨ C arm
e) Extra arm (variable arm)
ACCEPTOR ARM:
• It is at 3’ end
• It has 7 base pairs
• The end of the 3’ end are unpaired containing Cytosine, Cytosine-Adenine
• The 3’ OH- will bind to the carboxyl group of the amino acid

RAMDAS BHAT
• The t-RNA bound with the amino acid is called as the Amino-Acyl-tRNA
• The CCA attachment is done post transcriptionally.
ANTICODON ARM:
• They are present opp. to the acceptor arm
• They are 5 base pairs in length
• They will recognise the triplet codon present in the m RNA
• The base sequence of the Anticodon arm is complementary to the base sequence of mRNA
and anticodon will bind to the mRNA.
DHU ARM:
• They have 3-5 base pairs
• They act as the recognition site for the enzyme amino acyl t-RNA synthase that helps in
the addition of the m-RNA to the acceptor arm of the t-RNA.
TψC ARM:
• It is opposite to the DHU arm
• It has the pseudo uridine in it hence the name
• Helps in the binding of the t-RNA to the ribosomes.
VARIABLE ARM:
• Most of the T-RNA contain the variable arm
• They contain 3-5 base pairs.
r-RNA (RIBOSOMAL RNA):
• They are having 2 subunits
• The larger subunit with higher mol. Wt
• Lower subunit with lesser mol. Wt
• 60S subunit contain 5S ribosomal RNA, 5.8S and 28S
Ribosomal RNA.
• 40S subunit contain 18S Ribosomal RNA
• They help in the ribosomal assembly
• And help in the binding of the m RNA to the ribosomes and
their transcription

RAMDAS BHAT
DNA REPLICATION:
• DNA is a double stranded structure.
• The process of replication involves the cleavage of the double bond between the original
DNA molecule which is used as a template to form 2 separate DNA molecule containing
half of the original DNA molecule, Hence the process is called as SEMI CONSERVATIVE
PROCESS
• The process of the replication starts with the enzyme helicases acting on the DNA strand
• The enzyme breaks the bond between the DNA molecule along with the unwinding of the
helix into 2 single strands that acts as the template for the new DNA production.
• The formed structure is called REPLICATION FORK.
• Due to the formation of Replication form there will be formation of supercoiling of the
DNA molecule thus to prevent the tension and supercoiling of the DNA molecule enzyme
DNA topoisomerases will act over the segment of DNA present before the replication fork.
• The 5’ prime end-3’ prime is called as the leading strand and 3’ end to the 5’ end is called
as the lagging strand.
• The enzyme RNA primase adds up the RNA primer to the origin of replication
• The DNA POLYMERASE-3 adds up the new nucleotides to the leading strand from the 5’
end
• The RNA primer will act on the 3’ end of the lagging strand
• The DNA polymerase will help in the addition of the new nucleotide
• The formation of the strands in the 3’-5’ end is not Continous but fragments are formed
called OKAZAKI fragments.
• The DNA ligase will now seal the gap between the OKAZAKI fragments to form
Continous strand.

RAMDAS BHAT
RNA TRANSCRIPTION:
• Transcription is a process in which ribonucleic acid (RNA) ie mRNA is synthesized from
DNA.
• The word gene refers to the functional unit of the DNA that can be transcribe
• Thus, the information stored in DNA are expressed through the RNA
• Thus, one of the strands of the DNA acts as a template strand or a sense strand (non-Coding
strand) and produces RNA.
• Other strand which doesn't participate in the transcription is called as the ANTISENSE
STRAND or Coding strand.
The process of TRANSCRIPTION happens by 3 steps:
a) Initiation
b) Elongation
c) Termination
INITIATION:
• The process of the transcription happens by the attachment of RNA polymerase to the DNA
• The specific region on the DNA where the enzyme bind is called as the PROMOTER
REGION.
• This causes the double helix of the DNA to unwind and open.
• The template strand is used as a DNA strand for the attachment of the RNA polymerase
• The strand runs from 3’-5’
• And RNA polymerase can only prepare a new strand from 5’ to 3’ region.
ELONGATION:
• Here the RNA polymerase copies of the bases to the newly formed strand called as the
COMPLIMENTORY RNA STRAND.
• The RNA polymerase will follow the base pairs rules in order to express onto the newly
formed RNA.

RAMDAS BHAT
• The adenine copies the base uracil onto the mRNA
TERMINATION:
• The terminator region is present on the DNA molecule acts as a terminator end for the
stoppage of the transcription.
• Once the RNA polymerase reaches the terminator region the newly formed complimentary
RNA will get released from the site of transcription. Complimentary RNA is now called as
PRE-mRNA.
POST TRANSCRIPTIONAL CHANGES:
• Pre mRNA now formed is not matured for leaving the nucleus
• The get attached by the cap and a tail that prevents the formed RNA from the exonuclease’s
enzyme.
• Removal of the junk sequences that does not code for protiens called as introns. This
process is called as RNA splicing.
• This process happens by the presence of the enzyme called as SPLICEOSOME
• The end product of this mechanism is the matured RNA.
TRANSLATION:
• The process of production of the protiens from the mRNA is called as translation.
• The process happens in the presence of mRNA, tRNA, small and large subunit of ribosome
and the releasing factor.
• The mRNA contains the 3’ end called as the poly A tail and 5’ end called as the cap.
INITIATION:
• Newly formed mRNA will leave the nucleus and reaches the ribosome in the cytoplasm.
• The process involves the attachment on the subunits of the ribosome to the 5’ end of the
RNA.
• The tRNA contains the anticodon that codes for certain bases on the mRNA ie AUG.
• The amino acid binding site of the tRNA in the presence of Amino acid tRNA synthase
binds itself to the first amino acid molecule methionine.
• The ribosomes contains 3 sites ie E(exit), P(peptidyl), A(amino acyl)
• The t-RNA will bind to their matching bases ie AUG(UAC anticodon in t-RNA) and binds
to the A site contains corresponding base pair AUG.
ELONGATION:
• During this phase the Ribosome moves towards the poly A tail due to this displacement the
t-RNA will now move from A site to the P site and a new t-RNA having a corresponding
base (UUU) will bind to a site of the m-RNA containing AAA base forming a base pair.

RAMDAS BHAT
• The methionine of the 1st
t-RNA gets released and now it moves to the newly attached t-
RNA in the A- site and binds to the amino acid methionine.
• The process is Continous and the long amino acid polypeptide is formed.
TERMINATION:
• Once the ribosomes reach the terminal end the stop codon mechanism is activated by the
attachment of the releasing factor to the A site of m-RNA.
• Further no t-RNA gets attached and the t-RNA will now move on to the E site and the
amino acid polypeptide detaches itself from the t-RNA and the PROTIEN is now released.

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