The human genome contains around 3 billion base pairs that make up DNA organized into 23 chromosome pairs. Genes are sections of DNA that code for proteins, and can range in size from 1,000 to over 1.5 million base pairs. The human genome project mapped all human genes, finding around 20,000-25,000 genes, with only 1.1-1.4% of the genome actually coding for proteins. Genetic variations like single gene mutations or multiple gene effects can cause inherited diseases or influence disease risk.

1. Human Genome
DNA, Chromatine, Chromosomes
Genes
DNA Sequencing

2.  The human genome contains about 3 billion nucleotides also called base
pairs.
 Three nucleotides(base pairs) in the DNA codes for one amino acid

5.  Chromatin is a loop of DNA and histones containing about 100,000
nucleotide pairs.

6.  Humans have 46 chromosomes(23 pairs)

7.  Genes are Functional Units. That means that genes are not
microscopically visible, like the chromosomes or the chromatine.
 Geneticists divided the DNA into groups of nucleotides that code for
one single protein. This is called a gene.

8.  Genes can contain from 1,000 to more than 1.5 million nucleotides
(or base pairs) depending how large the protein they are coding for
are.
This protein is Titin. It consists of 27,000 amino acids.

9.  The human genome project was completed in 2003.
 It was established that human genome contains about 20,000 to
25,000 genes.
Journal Nature 2003

10.  Only 1.1% to1.4% of the genome's sequences code for proteins.
 Exons are coding regions, Introns are non-coding regions.

11.  Non-coding regions are initially copied into RNA, but they are left
out of the final RNA version (reason unknown).

12.  About 10% of the genes in the human genome encode for DNA binding
proteins(regulatory proteins).
 Some of these proteins recognize and attach to specific bits of DNA to
activate gene expression (ex. transcription factors, polymerases, nucleases)

13.  A genetic variation is a permanent change in the DNA sequence that
makes up a gene. Most variants are harmless or have no effects at
all.
 However, other variations can have harmful effects leading to
disease.

14.  Some genetic variations affect only a single gene.
 Single gene mutations are responsible for many rare inherited
neurological diseases.
 For example Huntington’s disease is a result of what is called an
expanded “triplet repeat” , a stutter in the huntingtin gene sequence.

15.  In the huntingtin gene, triplet repeats of 20 to 30
times are normal and cause no symptoms.
In people with Huntington’s disease, the number of
repeats reaches 40 or more.
The mutation creates an abnormally shaped protein
that is toxic to neurons.
As cells start to die, the symptoms of Huntington’s
disease appear. They consist of uncontrollable
writhing movements of the legs and arms, a loss of
muscle coordination, and changes in personality
and thinking.

16. Some cases of Lewy body dementia have been linked to having two or more
copies of the SNCA gene.
This gene encodes a protein called alpha-synuclein.
The excess alpha-synuclein accumulates inside the brain cells, jamming the
cells’ machinery.

17.  Some diseases show familial clustering but do
not conform to any recognized pattern of
single gene inheritance. They are termed
multifactorial or complex disorders.
 Multifactorial or complex disorders depend
on many genes and the environment.

18.  Geneticists search for connections between
genes and disease risk by performing three
kinds of studies:
Linkage Studies (using DNA or RNA)
Genome Wide Association Studies (using DNA)
Gene Expression Profiling (using RNA)
When a DNA or RNA portion is presumed to contain a
susceptibility locus for a disease, that area is red nucleotide
by nucleotide. This process is called DNA or RNA sequencing.

19. Regardless of which study is used, the end result is DNA or RNA sequencing. For this
purpose a device called a microarray, is employed. This is a small chip ( a gene
chip), coated with row upon row of DNA or RNA fragments.

20. Sequencing was once a time-
consuming and expensive
procedure, but a new set of
techniques called next-
generation sequencing has
emerged as an efficient, cost-
effective way to get a detailed
readout of the genome
For ex. the Lindsay's approach
has the potential to sequence
DNA at a speed of hundreds to
thousands of base pairs per
second.

21.  In laboratory, GWA studies and gene expression profiling studies are
leading to insights into new possibilities for disease prevention,
diagnosis and treatment.
 When geneticists identify a gene or gene regulatory pathway associated
with a disease, they uncover potential new targets for therapy.
 Understanding the relationship between genes and complex diseases
also is expected to play a role in personalized medicine.
 One day a microarray-based genome scanning could become a routine
way to estimate a person’s genetic risk of developing diseases like
stroke, Alzheimer’s disease, Parkinson’s disease and certain brain
cancers.
 Also researchers hope to develop customized drug “cocktails” that are
matched to a person’s unique genetic profile. Researchers believe that
these customized drugs will be much less likely than current medicines
to cause side-effects.