Medical Laboratory Techniques Department
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
1- Basic genetics
The laws of inheritance are investigated
by genetics. The different nucleic acids
(DNA and RNA) in the living organism play
a central role in the inheritance of the
different features. The information in the
DNA molecule is inherited from one
generation to the next generation through
reproduction. It means that the hereditary
material is the DNA (in some viruses the
RNA), more exactly the genes which are the functional units which determine the
nature of the features. Gene definition: Genes are the units of inheritance. Genes
are pieces of DNA that contain information for synthesis of ribonucleic acids
(RNAs) or polypeptides. Earlier only those units were regarded genes, which
coded proteins. Nowadays, genes are also those, which code functional RNAs,
which are not transcribed to proteins. These are called non-coding RNAs. In the
so-called RNA-viruses (e.g. influenza, HIV1) genes are coded only in the form of
RNA. The appearance of an organism which results from the expression of an
organism's genes as well as the influence of environmental factors and the
interactions between the two is called phenotype. The genetic background of an
organism is called genotype. The majority of the DNA content of the cells is
packaged in chromosomes and DNA can be also found in mitochondria. In diploid
cells a couple of homologous chromosomes are a set of one maternal chromosome
and one paternal chromosome that pair up with each other inside a cell during
meiosis. These copies have the same genes in the same locations, or loci. In the
nature a given gene can have different variations, these are called alleles. In a
given population the most frequent allele of a gene is called wild type. If in a
diploid cell the same alleles occur in a given locus of the homologous
chromosomes then the organism is homozygous, if the alleles are different, it is
heterozygous at this locus.
Page 1 of 79
, Medical Laboratory Techniques Department
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
1-2 Basics of molecular biology
The central dogma in molecular biology can be described as "DNA makes RNA
and RNA makes protein," a positive statement which was originally termed the
sequence hypothesis by Crick (Figure 1.2). However, this simplification does not
make it clear that the central dogma as stated by Crick does not preclude the
reverse flow of information from RNA to DNA, only ruling out the flow from
protein to RNA or DNA.
Figure 1.2. (The central dogma of molecular biology).
https://en.wikipedia.org/wiki/Central_dogma_of_molecular_biology#/media/File:Central_Dogma_of_Molecular_Bi
ochemistry_with_Enzym es.jpg 26/02/2016.
1-3 Some characteristics of the human DNA
The proteins coded by the DNA in our cells determine the structures and
functions of the cells. If there is a mutation in the DNA, it can change the structure
Page 2 of 79
, Medical Laboratory Techniques Department
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
and function of the protein, which can have consequences on the function of the
cell and can lead to diseases. Let‘s see the structure of the DNA in our cells. The
backbone of the DNA strand is made from alternating phosphate and sugar
residues (Figure 1.3). The sugar in DNA is 2-deoxyribose, which is a pentose
(five-carbon) sugar. The sugars are joined together by phosphate groups that form
phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar
rings. These asymmetric bonds mean a strand of DNA has a direction. In a double
helix the direction of the nucleotides in one strand is opposite to their direction in
the other strand: the strands are antiparallel. The asymmetric ends of DNA strands
are called the 5′ (five prime) and 3′ (three prime) ends, with the 5′ end having a
terminal phosphate group and the 3′ end a terminal hydroxyl group. One major
difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA
being replaced by the alternative pentose sugar ribose in RNA. The four bases
found in DNA are adenine (abbreviated A), cytosine(C), guanine (G) and thymine
(T). These four bases are attached to the sugar/phosphate to form the complete
nucleotide, as shown for adenosine monophosphate. The nucleobases are classified
into two types: the purines, A and G, being fused five- and six-membered
heterocyclic compounds, and the pyrimidines, the sixmembered rings C and T. A
fifth pyrimidine nucleobase, uracil (U), usually takes the place of thymine in RNA
and differs from thymine by lacking a methyl group on its ring. Uracil is not
usually found in DNA, occurring only as a breakdown product of cytosine .
In a DNA double helix, each type of nucleobase on one strand bonds with just one
type of nucleobase on the other strand. This is called complementary base pairing.
Here, purines form hydrogen bonds to pyrimidines, with adenine bonding only to
thymine in two hydrogen bonds, and cytosine bonding only to guanine in three
hydrogen bonds. This arrangement of two nucleotides binding together across the
double helix is called a base pair. As hydrogen bonds are not covalent, they can be
broken and rejoined relatively easily. The two strands of DNA in a double helix
can therefore be pulled apart like a zipper, either by a mechanical force or high
temperature. As a result of this complementarity, all the information in the double-
stranded sequence of a DNA helix is duplicated on each strand, which is vital in
DNA replication. Indeed, this reversible and specific interaction between
complementary base pairs is critical for all the functions of DNA in living
Page 3 of 79
, Medical Laboratory Techniques Department
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
organisms. A DNA sequence is called "sense" if its sequence is the same as that of
a messenger RNA copy that is translated into protein. The sequence on the
opposite strand is called the "antisense" sequence. Both sense and antisense
sequences can exist on different parts of the same strand of DNA (i.e. both strands
can contain both sense and antisense sequences). In human cells DNA is in two
compartments. Nuclear DNA, or nuclear deoxyribonucleic acid (nDNA), is DNA
contained within a nucleus of the cell. Nuclear DNA encodes for the majority of
the genome, with DNA located in mitochondria coding for the rest. Nuclear DNA
adheres to Mendelian inheritance, with information coming from two parents, one
male and one female. The other DNA containing compartment is the mitochondria.
Mitochondria are cellular organelles within eukaryotic cells that convert chemical
energy from food into a form that cells can use, adenosine triphosphate (ATP). In
most multicellular organisms, including humans the mitochondrial DNA (mtDNA)
is inherited from the mother (maternally inherited). Nuclear DNA and
mitochondrial DNA differ in many ways. The structure of nuclear DNA
chromosomes is linear with open ends and includes 46 chromosomes containing
more than 3 billion nucleotides (3.38 *109). Mitochondrial DNA chromosomes
have closed, circular structures, and contain 16,569 nucleotides. Nuclear DNA is
located within the nucleus of eukaryote cells and usually has two copies per cell
while mitochondrial DNA is located in the mitochondria and contains 100-1,000
copies per cell. Nuclear DNA contains more than 20 thousands protein coding and
more than 23 thousands non-coding genes. The mitochondrial DNA contains 37
genes. Of the 37 genes 13 are protein coding, 2 rRNA and 22 tRNA coding genes.
The mutation rate for nuclear DNA is less than 0.3% while that of mitochondrial
DNA is generally higher. As mitochondria is the ―powerhouse of the cell‖,
mutations of its DNA will effect on the power production processes of the cell, and
will have serious consequences especially in tissues with large power need, like
liver, neurons and muscle. As the mutation rate in the mitochondrial DNA higher,
the mitochondrial diseases usually deteriorate with age, and can play also a role in
the aging processes.
Page 4 of 79
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
1- Basic genetics
The laws of inheritance are investigated
by genetics. The different nucleic acids
(DNA and RNA) in the living organism play
a central role in the inheritance of the
different features. The information in the
DNA molecule is inherited from one
generation to the next generation through
reproduction. It means that the hereditary
material is the DNA (in some viruses the
RNA), more exactly the genes which are the functional units which determine the
nature of the features. Gene definition: Genes are the units of inheritance. Genes
are pieces of DNA that contain information for synthesis of ribonucleic acids
(RNAs) or polypeptides. Earlier only those units were regarded genes, which
coded proteins. Nowadays, genes are also those, which code functional RNAs,
which are not transcribed to proteins. These are called non-coding RNAs. In the
so-called RNA-viruses (e.g. influenza, HIV1) genes are coded only in the form of
RNA. The appearance of an organism which results from the expression of an
organism's genes as well as the influence of environmental factors and the
interactions between the two is called phenotype. The genetic background of an
organism is called genotype. The majority of the DNA content of the cells is
packaged in chromosomes and DNA can be also found in mitochondria. In diploid
cells a couple of homologous chromosomes are a set of one maternal chromosome
and one paternal chromosome that pair up with each other inside a cell during
meiosis. These copies have the same genes in the same locations, or loci. In the
nature a given gene can have different variations, these are called alleles. In a
given population the most frequent allele of a gene is called wild type. If in a
diploid cell the same alleles occur in a given locus of the homologous
chromosomes then the organism is homozygous, if the alleles are different, it is
heterozygous at this locus.
Page 1 of 79
, Medical Laboratory Techniques Department
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
1-2 Basics of molecular biology
The central dogma in molecular biology can be described as "DNA makes RNA
and RNA makes protein," a positive statement which was originally termed the
sequence hypothesis by Crick (Figure 1.2). However, this simplification does not
make it clear that the central dogma as stated by Crick does not preclude the
reverse flow of information from RNA to DNA, only ruling out the flow from
protein to RNA or DNA.
Figure 1.2. (The central dogma of molecular biology).
https://en.wikipedia.org/wiki/Central_dogma_of_molecular_biology#/media/File:Central_Dogma_of_Molecular_Bi
ochemistry_with_Enzym es.jpg 26/02/2016.
1-3 Some characteristics of the human DNA
The proteins coded by the DNA in our cells determine the structures and
functions of the cells. If there is a mutation in the DNA, it can change the structure
Page 2 of 79
, Medical Laboratory Techniques Department
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
and function of the protein, which can have consequences on the function of the
cell and can lead to diseases. Let‘s see the structure of the DNA in our cells. The
backbone of the DNA strand is made from alternating phosphate and sugar
residues (Figure 1.3). The sugar in DNA is 2-deoxyribose, which is a pentose
(five-carbon) sugar. The sugars are joined together by phosphate groups that form
phosphodiester bonds between the third and fifth carbon atoms of adjacent sugar
rings. These asymmetric bonds mean a strand of DNA has a direction. In a double
helix the direction of the nucleotides in one strand is opposite to their direction in
the other strand: the strands are antiparallel. The asymmetric ends of DNA strands
are called the 5′ (five prime) and 3′ (three prime) ends, with the 5′ end having a
terminal phosphate group and the 3′ end a terminal hydroxyl group. One major
difference between DNA and RNA is the sugar, with the 2-deoxyribose in DNA
being replaced by the alternative pentose sugar ribose in RNA. The four bases
found in DNA are adenine (abbreviated A), cytosine(C), guanine (G) and thymine
(T). These four bases are attached to the sugar/phosphate to form the complete
nucleotide, as shown for adenosine monophosphate. The nucleobases are classified
into two types: the purines, A and G, being fused five- and six-membered
heterocyclic compounds, and the pyrimidines, the sixmembered rings C and T. A
fifth pyrimidine nucleobase, uracil (U), usually takes the place of thymine in RNA
and differs from thymine by lacking a methyl group on its ring. Uracil is not
usually found in DNA, occurring only as a breakdown product of cytosine .
In a DNA double helix, each type of nucleobase on one strand bonds with just one
type of nucleobase on the other strand. This is called complementary base pairing.
Here, purines form hydrogen bonds to pyrimidines, with adenine bonding only to
thymine in two hydrogen bonds, and cytosine bonding only to guanine in three
hydrogen bonds. This arrangement of two nucleotides binding together across the
double helix is called a base pair. As hydrogen bonds are not covalent, they can be
broken and rejoined relatively easily. The two strands of DNA in a double helix
can therefore be pulled apart like a zipper, either by a mechanical force or high
temperature. As a result of this complementarity, all the information in the double-
stranded sequence of a DNA helix is duplicated on each strand, which is vital in
DNA replication. Indeed, this reversible and specific interaction between
complementary base pairs is critical for all the functions of DNA in living
Page 3 of 79
, Medical Laboratory Techniques Department
Title of the lecture: Human Genetic
Dr.: Zahraa Haleem Alqiam
@mustaqbal-college.edu.iq
organisms. A DNA sequence is called "sense" if its sequence is the same as that of
a messenger RNA copy that is translated into protein. The sequence on the
opposite strand is called the "antisense" sequence. Both sense and antisense
sequences can exist on different parts of the same strand of DNA (i.e. both strands
can contain both sense and antisense sequences). In human cells DNA is in two
compartments. Nuclear DNA, or nuclear deoxyribonucleic acid (nDNA), is DNA
contained within a nucleus of the cell. Nuclear DNA encodes for the majority of
the genome, with DNA located in mitochondria coding for the rest. Nuclear DNA
adheres to Mendelian inheritance, with information coming from two parents, one
male and one female. The other DNA containing compartment is the mitochondria.
Mitochondria are cellular organelles within eukaryotic cells that convert chemical
energy from food into a form that cells can use, adenosine triphosphate (ATP). In
most multicellular organisms, including humans the mitochondrial DNA (mtDNA)
is inherited from the mother (maternally inherited). Nuclear DNA and
mitochondrial DNA differ in many ways. The structure of nuclear DNA
chromosomes is linear with open ends and includes 46 chromosomes containing
more than 3 billion nucleotides (3.38 *109). Mitochondrial DNA chromosomes
have closed, circular structures, and contain 16,569 nucleotides. Nuclear DNA is
located within the nucleus of eukaryote cells and usually has two copies per cell
while mitochondrial DNA is located in the mitochondria and contains 100-1,000
copies per cell. Nuclear DNA contains more than 20 thousands protein coding and
more than 23 thousands non-coding genes. The mitochondrial DNA contains 37
genes. Of the 37 genes 13 are protein coding, 2 rRNA and 22 tRNA coding genes.
The mutation rate for nuclear DNA is less than 0.3% while that of mitochondrial
DNA is generally higher. As mitochondria is the ―powerhouse of the cell‖,
mutations of its DNA will effect on the power production processes of the cell, and
will have serious consequences especially in tissues with large power need, like
liver, neurons and muscle. As the mutation rate in the mitochondrial DNA higher,
the mitochondrial diseases usually deteriorate with age, and can play also a role in
the aging processes.
Page 4 of 79
