In this ppt you will find what is Gene, nature of Gene, regulatory elements of Gene, Non coding DNA, Alleles, Molecular nature of alleles. #GENE #ALLELE #DNA

1. Gene basics
Dr. Naeem Ullah
PhD Medical Lab sciences
M.phil in Medical Lab Sciences
BS in medical Lab Sciences
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Dr. Naeem Ullah

2. Gene?
• A gene is the basic physical and functional unit of heredity.
• Genes are made up of DNA. Some genes act as instructions to make
molecules called proteins.
• However, many genes do not code for proteins.
• In humans, genes vary in size from a few hundred DNA bases to more
than 2 million bases.
• The Human Genome Project estimated that humans have between
20,000 and 25,000 genes.
• 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 between people.
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3. Gene
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4. Nature of gene?
• Three fundamental properties are required of genes and the DNA of
which they are composed.
1. Replication: Hereditary molecules must be capable of being copied at
two key stages of the life cycle.
A. The first stage is the production of the cell type that will
ensure the continuation of a species from one generation
to the next. In plants and animals, these cells are the
gametes: egg and sperm.
B. The other stage is when the first cell of a new organism
undergoes multiple rounds of division to produce a
multicellular organism. In plants and animals, this is the
stage at which the fertilized egg, the zygote, divides
repeatedly to produce the complex organismal appearance
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5. Nature of gene?
2. Generation of form: The working structures that make up an organism
can be thought of as form or substance, and DNA has the essential
“information” needed to create form.
• Phenotype vs Genotype?
3. Mutation: A gene that has changed from one allelic form into another has
undergone mutation —an event that happens rarely but regularly.
• Mutation is not only a basis for variation within a species, but also, over
the long term, the raw material for evolution.
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6. Non coding DNA
• Only about 1% of DNA is made up of protein-coding genes; the other
99% is noncoding.
• Noncoding DNA does not provide instructions for making proteins.
• Scientists once thought noncoding DNA was “junk,” with no known
purpose.
• However, it is becoming clear that at least some of it is integral to the
function of cells, particularly the control of gene activity.
• For example, noncoding DNA contains sequences that act as
regulatory elements, determining when and where genes are turned on
and off.
• Such elements provide sites for specialized proteins (called
transcription factors) to attach (bind) and either activate or repress the
process by which the information from genes is turned into proteins
(transcription). 6
Dr. Naeem Ullah

7. Non coding DNA
• Noncoding DNA contains many types of regulatory elements:
• Promoters: provide binding sites for the protein machinery that carries
out transcription.
• Promoters are typically found just ahead of the gene on the DNA
strand.
• Enhancers: provide binding sites for proteins that help activate
transcription.
• Enhancers can be found on the DNA strand before or after the gene
they control, sometimes far away.
• Silencers: provide binding sites for proteins that repress transcription.
• Like enhancers, silencers can be found before or after the gene they
control and can be some distance away on the DNA strand.
• Insulators: provide binding sites for proteins that control transcription
in a number of ways.
• Some prevent enhancers from aiding in transcription (enhancer-
blocker insulators).
• Others prevent structural changes in the DNA that repress gene
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8. Regulatory elements
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9. Regulatory elements
• Other regions of noncoding DNA provide instructions for the formation of
certain kinds of RNA molecules.
• Examples of specialized RNA molecules produced from noncoding DNA
include:
– transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which help assemble
protein building blocks (amino acids) into a chain that forms a protein;
– microRNAs (miRNAs), which are short lengths of RNA that block the process of
protein production
– long noncoding RNAs (lncRNAs), which are longer lengths of RNA that have
diverse roles in regulating gene activity.
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10. Regulatory elements
• Repeated noncoding DNA sequences at the ends of
chromosomes form telomeres.
– Telomeres protect the ends of chromosomes from being
degraded during the copying of genetic material.
• Repetitive noncoding DNA sequences also form satellite
DNA, which is the basis of the centromere.
• Satellite DNA also forms heterochromatin, which is
densely packed DNA that is important for controlling gene
activity and maintaining the structure of chromosomes.
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11. Conti...
• Some noncoding DNA regions, called introns, are located
within protein-coding genes but are removed before a
protein is made.
• Regulatory elements, such as enhancers, can be located
in introns.
• Other noncoding regions are found between genes and
are known as intergenic regions.
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12. Alleles?
• Alleles are forms of the same gene with small differences in their
sequence of DNA bases.
• These small differences contribute to each person’s unique physical
features.
• Alleles segregate during meiosis, and an individual receives only one of
each pair of alleles from each parent.
• Only two alleles can be present in any one individual.
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13. What is the molecular nature of alleles?
• When alleles such as A and a are examined at the DNA level, they are
generally found to be identical in most of their sequences and differ
only at one or a few nucleotides of the thousands of nucleotides that
make up the gene.
• Therefore, we see that the alleles are truly different versions of the
same basic gene.
• Looked at another way, gene is the generic term and allele is specific.
• (The pea-color gene has two alleles coding for yellow and green.)
• The letter “x” represents a difference in the nucleotide sequence
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14. Allele
• In studying any kind of variation such as allelic variation, it is often
helpful to have a standard to act as a fixed reference point.
• In genetics “wild type” is the allele used as the standard; it is the form of
any particular gene that is found in the wild, in other words in
natural populations.
• Homozygous: Having two identical alleles for a particular gene
• Heterozygous: Having two different alleles for a particular gene
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15. Allele
• Genotype: An individual’s genetic constitution; the alleles present at
one locus
• Phenotype: The observed biochemical, physiological, and morphological
characteristics of an individual (e.g., blue eyes, fair skin), as determined
by his or her genotype and the environment in which it is expressed
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16. References
• An Introduction to Genetic Analysis, Eighth Edition
by Anthony J.F. Griffiths (U. of British Columbia)
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