002.genetics

Tanveer Tara Lecturer MLT ,Institute of Biological Sciences
,Sarhad University
1

Introduction
• GENETICS is the branch of science that deals with heredity and
variation(somatic & germinal) in organisms
• It include the genetic features and constitution of a single organism,
species, or group
• Approaches to genetic basis of diseases.
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Inheritance Pattern
• Classical Mendelian pattern
• Non Classical Mendelian pattern
Classical Mendelian pattern
Autosomal (1-22)
Dominant Recessive
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Classical Mendelian pattern
Sex Chromosome Linked Disorder
X-Linked Y-Linked ( Very rare)
Dominant Recessive
Dominant Recessive
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Non Classical Mendelian pattern
• Non-Mendelian inheritance is any pattern of inheritance in
which traits do not segregate in accordance with Mendel's laws.
These laws describe the inheritance of traits linked to single
genes on chromosomes in the nucleus. ... Non-Mendelian
Inheritance is applicable in co-dominance and incomplete
dominance
• Polygenic traits are considered non-Mendelian because their
alleles are located on more than one gene which allows for more
alleles and phenotypes.
• Examples of polygenic traits are hair color and height. Other
traits, such as blood type, show codominance, where there is no
dominant or recessive allele.
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Basic
CONCEPT
Chromosome
Gene Allele Locus
Homologues Chromosome
Dominance
Recessiveness
Genotype Phenotype
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Chromosome
• A threadlike structure of nucleic acids and protein found in the
nucleus of most living cells, carrying genetic information in the
form of genes.
• 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.
• Organisms grow by undergoing cell division to produce new cells
and replace older, wornout cells. During this cell division, DNA
must remain intact and keep its even distribution throughout the
cells. Chromosomes are important to this process to ensure the
DNA is accurately replicated.
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Chromosome
• Males have one Y chromosome and
one X chromosome, while
females have two X chromosomes.
In mammals, the Y
chromosome contains a gene, SRY,
which triggers embryonic
development as a male. The Y
chromosomes of humans and other
mammals also contain other genes
needed for normal sperm
production.
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Boveri-Sutton Chromosome Theory
• Boveri-Sutton developed the chromosome theory of inheritance in
1902.
• Each chromosome has many genes
• Paired chromosomes segregate during meiosis.
• Chromosomes assort independently during meiosis
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Chromosome structure
• Each chromatid consists of a
very long strand of DNA
• The DNA is roughly co-linear
with the chromosome but is
highly structured around histones
and other proteins which serve to
condense its length and control
the activity of genes
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11

Telomeres
Centromere
Specialized structures
at chromosome ends
that are important for
chromosome stability.
A region within chromosomes
that is required for proper
segregation during meiosis
and mitosis.
Key chromosomal regions
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Classification (karyotype)
Chromosomes can be classified according to size and
form, and numbered of large to small.
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Types
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Types of Chromosomes
• Chromosomes are divided into two parts (p and
q arms) with a constriction point called a
centromere in the middle.
• The centromere can be located in different
positions and this forms the basis for the four
different classes of chromosome:
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Chromosome
• Metacentric – centromere is in middle,
meaning p and q arms are of comparable
length (e.g. chromosomes 1, 3, 16, 19, 20)
Submetacentric – centromere off-center,
leading to shorter p arm relative to q arm
(e.g. chromosomes 2, 4 – 12, 17, 18, X)
Acrocentric – centromere severely off-set
from center, leading to much shorter p arm
(e.g. chromosomes 13 – 15, 21, 22, Y)
Telocentric – centromere found at end of
chromosome, meaning no p arm exists
(chromosome not found in humans)
•
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Human Genome
Most human cells
contain 46 chromosomes:
• 3 billion base pairs
• between 20,000 and 25,000 genes.
• 2 sex chromosomes (X,Y):
XY – in males.
XX – in females.
• 22 pairs of chromosomes named
autosomes.

Nucleotide sequences
• Nucleotide sequences is concerned with
specific RNA (gene)
• DNA has Many gene.
• 4 types of RNA, each encoded by its own type
of gene:
• mRNA - Messenger RNA: Encodes amino acid
sequence of a polypeptide.
• tRNA - Transfer RNA: Brings amino acids to
ribosomes during translation.
• rRNA - Ribosomal RNA: With ribosomal
proteins, makes up the ribosomes, the
organelles that translate the mRNA.
• snRNA - Small nuclear RNA: With proteins,
forms complexes that are used in RNA
processing in eukaryotes. (Not found in
prokaryotes.)
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Chromosome
number in
various
Organism
Tanveer Tara Lecturer MLT ,Institute of Biological Sciences ,Sarhad University 20

46 CHROMOSOME

Gene
A Sequence of nucleotide in DNA which is concerned with formation of specific RNA.
Gene is a sequence of nucleotides in DNA or RNA that codes for a molecule that has a
function. During gene expression, the DNA is first copied into RNA. The RNA can be
directly functional or be the intermediate template for a protein that performs a function.

Allele
Any of two or more variants of a gene that have
the same relative position on homologous
chromosomes and are responsible for
alternative characteristics, such as smooth or
wrinkled seeds in peas Also called: allelomorph.
An allele is a variant form of a given gene
sometimes, the presence of different alleles of
the same gene can result in different
observable phenotypic traits, such as
different pigmentation.

Multiple
Allele.
Three or more alternative forms of a gene
(alleles) that can occupy the same locus.
However, only two of the alleles can be present in
a single organism. For example, the ABO system
of blood groups is controlled by three alleles, only
two of which are present in an individual.
"multiple alleles."

Monogenic
disorders :
Monogenic disorders :
Inherited Disorder which are defective by one
gene. The mutation may be present on one or
both chromosomes (one chromosome inherited
from each parent).
Examples of monogenic disorders are:
sickle cell disease,
cystic fibrosis,
polycystic kidney disease,
Tay-Sachs disease
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Polygenic trait
Polygenic trait is one whose phenotype is
influenced by more than one gene
A trait that is controlled by a group of nonallelic
genes (called polygene). Polygenic traits are
controlled by two or more than two genes
(usually by many different genes) at different loci
on different chromosomes. These genes are
described as polygenes
height, skin color, eye color and weigh

Gene for eye color
• OCA2 and HERC2
• There is evidence that as many as
16 different genes could be
responsible for eye color in
humans; however, the main two
genes associated with eye color
variation are OCA2 and HERC2,
and both are localized
in Chromosome 15.

Locus
• A locus (plural loci) in genetics is a fixed position on a chromosome,
like the position of a gene or a marker (genetic marker). Each
chromosome carries many genes; human's estimated
'haploid' protein coding genes are 19,000–20,000, on the 23 different
chromosomes.
• A variant of the similar DNA sequence located at a given locus is
called an allele. The ordered list of loci known for a
particular genome is called a gene map.
• Gene mapping is the process of determining the locus for a
particular biological trait.
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Locus , Allele
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Genotypes
• The genotype is the set of genes in our DNA which is responsible for a
particular trait..
• There are three available genotypes,
• PP (homozygous dominant),
• Pp (heterozygous),
• pp (homozygous recessive).
• All three have different genotypes but the first two have the same
phenotype (purple) as distinct from the third (white).
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Genotype
• Genotype is what makes the trait - the information within a gene, or
the genetic makeup of a specific organism. Genotype is determined
by the makeup of something called "alleles,"
• Genotype is the information contained within two alleles.
• The genetic makeup of an organism and it results in some of the
physical characteristics of that organism.
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Genotypes
• Genotypes can only be determined by biological tests, not
observations.
• Genotype is an inherited trait and hereditary information passed by
the parents determines genotype.
• The entire genetic information about an organism is contained in a
genotype - even those characteristics which are not expressed visually
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EXAMPLE :
• If someone has blood type A,
they must have at least one
copy of the A allele, but they
could have two copies.
Their genotype is either AA or
AO. Similarly, someone who
is blood type B could have
a genotype of either BB or
BO. ... Someone with blood
type AB must have both the A
and B alleles.
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Examples of genotype are the genes responsible for:
• Eye color
• Hair color
• Height
• How your voice sounds
• Certain diseases
• Certain behaviors
• The size of a bird's beak
• The length of a fox's tail
• The color of stripes on a cat
• The spots on a dog's back
• A person's shoe size
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Phenotype
• The phenotype is the physical expression, or characteristics, of that
trait.
• For example, two organisms that have even the minutest difference in
their genes are said to have different genotypes. These two mice may
have different genotypes and both can still be white if they share the
particular phenotype for white fur.
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Phenotype is what you see
• Phenotype is what you see - the visible or observable expression of
the results of genes, combined with the environmental influence on
an organism's appearance or behavior. For example:
• It is the expression of gene information which is observable with the
senses (like the sound of a bird's chirping or the color of a cat's hair)
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Phenotype can be determined by mere, simple observation. Examples
of phenotypes are the actual visible characteristics including:
• Eye color
• Hair color
• Height
• Sound of your voice
• Certain types of disease
• Certain behaviors
• Size of a bird's beak
• Length of a fox's tail
• Color of the stripes on a cat
• Size and shape of the spots on a dog's back
• An individual's shoe size
,Sarhad University
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Homozygous
• Diploid and polyploid cells whose chromosomes have the same allele
of a given gene at some locus are called homozygous with respect to
that gene.
• Homozygous is a word that refers to a particular gene that has
identical alleles on both homologous chromosomes.
• It is referred to by two capital letters (XX) for a dominant trait, and
two lowercase letters (xx) for a recessive trait.
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Heterozygous
• while those that have different alleles of a given gene at a locus are
called heterozygous with respect to that gene.
• Heterozygous means having one each of two different alleles.
• The fact that males are hemizygous for sex-linked alleles is the reason
X-linked recessive phenotypes are more commonly observed in
males. Females can be heterozygous for a trait and therefore carry
the recessive allele without expressing it.
• If the organism's genotype is Bb, the dominant allele will be seen, but
the organism will still be "carrying" a gene for the recessive trait. In
each sperm or egg, one of these alleles will be passed down.
,Sarhad University
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Trait :
• Dominant trait will always be expressed in the offspring if
the dominant allele is present, even if there is only one copy of it
(heterozygous or dominant homozygous, Aa or AA).
• Recessive traits can be carried in a person's genes without appearing
in that person. For example, a dark-haired person may have one gene
for dark hair, which is a dominant trait, and one gene for light hair,
which is recessive.
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Codominance
• Codominance is a form of dominance where in the alleles of a gene
pair in a heterozygote are fully expressed. This results in offspring
with a phenotype that is neither dominant nor recessive.
• A typical example showing codominance is the ABO blood group
system.is a form of dominance wherein the alleles of a gene pair in a
heterozygote are fully expressed. This results in offspring with a
phenotype that is neither dominant nor recessive. A typical example
showing codominance is the ABO blood group system.
,Sarhad University
41

Summary
• Gene – basic unit of genetic
information. Genes determine the
inherited characters.
• Genome – the collection of genetic
information.
• Human Genome is set of genetic
information encoded as DNA within 23
pair of chromosomes in nuclei.
• Chromosomes – storage units of genes.

Continued…
DNA - is a nucleic acid that contains the
genetic instructions specifying the
biological development of all cellular
forms of life
Locus – location of a gene/marker on the
chromosome.
Allele – one variant form of a
gene/marker at a particular locus.

Gene
• The gene is the basic physical and functional
unit of heredity.
• It consists of a specific sequence of
nucleotides at a given position on a given
chromosome

Continued…
• Genes consist of three types of nucleotide sequence:
•coding regions, called exons, which specify a sequence of amino acids
•non-coding regions, called introns, which do not specify amino acids
•regulatory sequences, which play a role in determining when and where the
protein is made
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Important
Terms
Homozygous: Both genes provide same
instruction
Heterozygous: The gene provide conflicting
instructions
Dominant Gene: Show traits when present
or always determines development (one
allele present)
Recessive Gene: Recessive alleles only show
their effect if the individual has two copies
of the allele

,Sarhad University
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Some Facts
• In human beings, 99.9% bases are same
• Remaining 0.1% makes a person unique
• Different attributes / characteristics / traits
• how a person looks
• diseases he or she develops
• These variations can be:
• Harmless (change in phenotype)
• Harmful (diabetes, cancer, heart disease, Huntington's disease and
hemophilia)
• Latent (variations found in coding and regulatory regions, are not
harmful on their own, and the change in each gene only becomes apparent
under certain conditions e.g. susceptibility to heart attack)
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,Sarhad University
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Types of Chromosome Abnormalities
The human body has 20,000 to 25,000 different genes. Genes are located on chromosomes,
which are stick-shaped structures in the middle of each cell in the body. Each cell usually has 46
chromosomes grouped in 23 pairs. Each gene has a specific function. And when a gene or
chromosome is abnormal, it may cause health problems in the body.
There are 2 main types of genetic changes:
•Chromosome abnormalities
•Single-gene defects

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Can Human sperm fertilize animal eggs? We hear about animals producing human-like creatures, how
do their ovules get fertilized by human sperm, is it possible anyway?
First, sperm have to find their way to an egg. In mammals, when the egg is released from the ovary it is
surrounded by a loose group of follicle cells. These cells release a chemical signal that the sperm swim toward.
If the signal is not correct, the sperm won't find the egg.
While the sperm are swimming up the female's reproductive tract, ions that her body secretes are absorbed
into the sperm cells, causing internal changes that are referred to as capacitation. In humans, capacitation
takes 5 to 6 hours and must be completed before the sperm can accomplish its next job, which is to penetrate
the zona pellucida, or egg coat. The zona pellucida has proteins that are similar to the proteins used by the
immune system, and these proteins make cross-species fertilization nearly impossible.
Once the sperm has successfully penetrated the zona pellucida, the acrosome reaction allows the sperm to
fuse with the membrane of the egg so that the male's DNA can enter the egg cell. The acrosome reaction
requires specific proteins that again prevent hybridization between species.
In order for cell division to occur and create an embryo, the paternal and maternal DNA must line up - another
block to hybridization, as DNA varies from species to species enough for this to be unlikely to work.
An interesting side note is that fertility clinics sometimes use enzymes to strip the zona pellucida away from
hamster eggs, and then use the stripped eggs to test human sperm for penetrating power. Although healthy
sperm can penetrate the hamster eggs in this case, the DNA alignment fails and the fertilized eggs die without
undergoing mitosis.

002.genetics

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