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By the end of this section, you will be able to:
  • Describe three types of sequencing
  • Define whole-genome sequencing

Although there have been significant advances in the medical sciences in recent years, doctors are still confounded by some diseases, and they are using whole-genome sequencing to get to the bottom of the problem. Whole-genome sequencing is a process that determines the DNA sequence of an entire genome. Whole-genome sequencing is a brute-force approach to problem solving when there is a genetic basis at the core of a disease. Several laboratories now provide services to sequence, analyze, and interpret entire genomes.

For example, whole-exome sequencing is a lower-cost alternative to whole genome sequencing. In exome sequencing, only the coding, exon-producing regions of the DNA are sequenced. In 2010, whole-exome sequencing was used to save a young boy whose intestines had multiple mysterious abscesses. The child had several colon operations with no relief. Finally, whole-exome sequencing was performed, which revealed a defect in a pathway that controls apoptosis (programmed cell death). A bone-marrow transplant was used to overcome this genetic disorder, leading to a cure for the boy. He was the first person to be successfully treated based on a diagnosis made by whole-exome sequencing. Today, human genome sequencing is more readily available and can be completed in a day or two for about $1000.

Strategies used in sequencing projects

The basic sequencing technique used in all modern day sequencing projects is the chain termination method (also known as the dideoxy method), which was developed by Fred Sanger in the 1970s. The chain termination method involves DNA replication of a single-stranded template with the use of a primer and a regular deoxynucleotide    (dNTP), which is a monomer, or a single unit, of DNA. The primer and dNTP are mixed with a small proportion of fluorescently labeled dideoxynucleotides (ddNTPs). The ddNTPs are monomers that are missing a hydroxyl group (–OH) at the site at which another nucleotide usually attaches to form a chain ( [link] ). Each ddNTP is labeled with a different color of fluorophore. Every time a ddNTP is incorporated in the growing complementary strand, it terminates the process of DNA replication, which results in multiple short strands of replicated DNA that are each terminated at a different point during replication. When the reaction mixture is processed by gel electrophoresis after being separated into single strands, the multiple newly replicated DNA strands form a ladder because of the differing sizes. Because the ddNTPs are fluorescently labeled, each band on the gel reflects the size of the DNA strand and the ddNTP that terminated the reaction. The different colors of the fluorophore-labeled ddNTPs help identify the ddNTP incorporated at that position. Reading the gel on the basis of the color of each band on the ladder produces the sequence of the template strand ( [link] ).

A deoxynucleotide consists of a deoxyribose sugar, a base, and three phosphate groups. Dideoxyribose is identical to deoxyribose except that the hydroxyl (–OH) group at the 3' position is replaced by H. A 3' hydroxyl is necessary for elongation of the DNA chain, and the chain therefore stops growing if a dideoxyribose instead of deoxyribose is incorporated into the growing chain.
A dideoxynucleotide is similar in structure to a deoxynucleotide, but is missing the 3' hydroxyl group (indicated by the box). When a dideoxynucleotide is incorporated into a DNA strand, DNA synthesis stops.

Questions & Answers

diagram of Prokaryotic cells
Magreth Reply
where is it?
Yazi
ʜɪ
Malikie
ʜɪ
Malikie
where is the diagram?
Yazi
waiting.....
Yazi
what
Malikie
good morning guyz
Joelia
gd morning
Hannalyn
morning how are u doing
Paul
doing all fyn en u
Joelia
👍👍👍
Gruxz
morning everyone.. by is Grace we have be saved... Ephesians 2:8....
Cosmo
what is a cell of a bacteria called
Sahfe Reply
what is genotype
James
genotype: this is the combination of alleles an organism has for a given characteristic..
Cosmo
what is maiotic
Gabriel Reply
what is sexual reproduction
Gabriel
what are the effects of concentration gradient in the uptake of water by plant's
Harleen Reply
ls it ok if you have sex during pregnancy
Kags Reply
no
Bernard
yes!!!
Yazi
Yes
Babie
hello
Cabdi
Babie Maseuse .. Hello .. how are you ?
kf
yes it make the baby's strength stay longer
REAL
Who are you?
Babie
why not it's nicer and more enjoyable more than ok for the woman
Lamin
danso from the Gambia and you why do you ask
Lamin
as long as the woman is comfortable and in any possible position good for her
Lamin
unless medically advised to stop or hault and those conditions are also applicable to certain problem in pregancies. Pls any further comment pls never hesitate to ask
Lamin
how tell us
Tony
an assignment for you pls
Lamin
it's recommended
Nyakato
Hello
george
hi how are you?
Lamin
Fine
george
hello everyone
Cosmo
Good night to everyone am from Zambia may the Grace of the Lord be with you all
Cosmo
u too hv gd dreams
Joelia
thanks colleagues and wish you all the best insha Allah
Lamin
InshaAllah
Joelia
Marsha Allah
Lamin
yes
James
What is the meaning of organ
Ronald Reply
tissue combined to form organ
zameer
join
Elishs
orga- these are tissues join together to perform a specific functions.
Elishs
then what are tissues
Kags
group of cells working together to perform a particular function
Harleen
tissue are group of cells put together to perform a certain goal
Bernard
What will happen when read blood cell placed in 0.5 % Nacl solution
zameer Reply
what is biology
Tariro Reply
biology is the study of living organisms
Bernard
examply is the study of.
Nantamu
biology is the study of life.
Nantamu
what is biology
Francis Reply
kidny with large and and many glomeruli are characcteristic feathure of ?
zameer
Can you please put up the notes for antibiotics
Jesus Reply
I can't
Francis
we should first know what is antibiotics.what is antibiotics.
Francis
A cell is the basic functional unit of life.
Jael
what is a cell ?
Rabecca Reply
A cell is the basic functional unit of all organisms
Glandwell
A cell is a basic functional and structural unit of life.
Mavis
please, emphasize more on the coronary circuit
Toyyiba Reply
define the photosynthesis
Sabrinah Reply
list the type of protein
Sabrinah
sugar.glucose
Tamirat
renin,pepsin
Nyakato
peptides
Nyakato
what is photosynthesis
Francis
what is biology
Nathan Reply
branch of science which deal with living and non living things
zameer
different branches of biology
linus
zameer is right
Onuoha
we don't study non living things in biology
mejury
biology is simply the study of life
Toyyiba
biology can simply be the branch of science that deals with the study of flora and fauna
Nyakato
Biology is the study of life
Peace
What is Diffusion
Soliu
The word "Bio" means life and "Logy" means study or knowlegde". Biology is the study of Life (living organisms from microorganisms to plant and animals), their behaviour, mode of living, actions, e.t.c
adewunmi
Bio means life and logy means study of so in other words Biology means study of life
Peace
what is zameer
Francis
what is biology
Pamodou Reply
is the study of life
George
Biology is the study of life
Peace
the word "Bio" is the greek word for "Life" while "Logy" is the knowledge, study of Life. Therefore, Biology is the study or knowledge of life in which case can be from micro organism to plants to animals, their mode of life, features, characteristics, survival e.t.c
adewunmi
biology is the study of living organisms
mejury
study of living organisms
Moses

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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