3.1 Chromosomes, genes, alleles, mutations

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Transcript 3.1 Chromosomes, genes, alleles, mutations

IB Assessment State
• State that eukaryote chromosomes are made of DNA
and proteins.
DNA and Chromosomes.
DNA is the
large molecule
that makes up
in cells.
DNA and Chromosomes
• DNA and Chromosomes
• In prokaryotic (i.e. bacteria) cells, DNA is
located in the cytoplasm.
• Most prokaryotes have a single DNA
molecule containing nearly all of the cell’s
genetic information.
• Prokaryotes’ chromosomes have NO
associated proteins
DNA and Chromosomes
E. Coli Bacterium
Bases on the
DNA and Chromosomes
• Many eukaryotes (i.e. humans, fish) have
1000 times the amount of DNA as
• Eukaryotic DNA is located in the cell
nucleus inside chromosomes.
• The number of chromosomes varies
widely from one species to the next.
DNA and Chromosomes
– Chromosome Structure
• Eukaryotic chromosomes contain
DNA and protein, tightly packed
together to form chromatin.
• Chromatin consists of DNA tightly
coiled around proteins called
DNA and Chromosomes
– Eukaryotic Chromosome Structure
• Animation about Eukaryotic DNA COILING
• http://www.biostudio.com/demo_freeman_
IB Assessment Statement
• Define gene, allele and genome.
Genetics – the study of inheritance and of
variation of inherited characteristics
that chromosomes control.
Key Vocabulary
• Gene – a heritable factor that controls a
specific characteristic.
• Allele – one specific form of a gene,
differing from other alleles (example blue
• Genome – the whole genetic
information of the organism.
IB Assessment Statement
• Define gene mutation.
• Explain the consequence of a base
substitution mutation in relation to the
processes of transcription and translation,
using the example of sickle-cell anemia.
• GAG has mutated to GTG causing
glutamic acid to be replaced by valine, and
hence sickle-cell anemia.
Consequence of a base substitution mutation
– A point mutation is a single base
substitution, is a type of mutation that
causes the replacement of a single base
nucleotide with another nucleotide of the
genetic material, DNA or RNA
• Causes of Sickle Cell Anemia
– A base substitution mutation in DNA in the
gene that codes for hemoglobin
Sickle Cell Causes
• The Normal allele has a ‘A’ – adenine(a
nitrogenous base in a nucleotide in DNA)
and codes for the GAG = glutamic acid.
• The sickle allele has and ‘T’ –Thymine
(a nitrogenous base in a nucleotide in
DNA) and codes for the GTG valine
amino acid
Genetic Causing of Sickle Cell
Normal Hemoglobin
The hemoglobin molecule picks up oxygen in the
lungs and releases it when the red cells reach
tissues, such as the muscles.
• Normal hemoglobin molecules exist as single,
isolated units in the red cell, whether they
have oxygen bound or not.
• Normal red cells maintain a basic disc shape,
whether they are transporting oxygen or not.
Sickle cell hemoglobin
• Sickle hemoglobin exist as isolated units
in the red cells when they have oxygen
• .
Sickle cell hemoglobin
When sickle hemoglobin releases oxygen
in the p tissues, the molecules tend to
stick together and form long chains or
Sickle cell hemoglobin
These rigid polymers distort
the cell and cause it to
bend out of shape.
• While most distorted cells
are simply shaped
irregularly, a few have a
cresent-like appearence
under the microscope.
Sickle-shaped red blood cells
• Sickle Hemoglobin deforms the shape of
the red cells.
• The problem is not simply one of abnormal
• The membranes of the red blood cells
are rigid due to hemoglobin
• These rigid cells
fail to move
through the
small blood
blocking local
blood flow to a
region of tissue.
• Amplified many times, these episodes
produce tissue hypoxia (low oxygen
supply). The result is pain, and often
damage to organs.
Consequences of Sickle Cell
• Life expectancy is shortened, with studies
reporting an average life expectancy of
42 in males and 48 in females
Inheritance of the Sickle Cell trait
• The gene for
sickle cell is
recessive (Hbs)
• To have sickle
cell anemia you
have to have
inherited it
from both
Inheritance of the Sickle Cell trait
• Some one who is
a heterozygote
(inherited normal
gene and a sickle
cell gene from
parents) for sickle
cell anemia is called
a carrier of sickle
cell anemia.
Carriers of Sickle Cell
• The gene for sickle cell is incompletely
• Carriers (heterozygoussickle cell trait) can
produce a few sickled red blood cells,
not enough to cause symptoms,
Why do harmful Alleles Survive
over time?
• If natural selection eliminates individuals
with detrimental phenotypes from a
population, then why do harmful mutant
alleles persist in a gene pool?
Sickle Cell Anemia and Malaria
Distribution of Malaria
Distribution of Sickle
Cell Anemia Cases
• Malaria is a female-mosquitoborne infectious disease
caused by a eukaryotic protist
of the genus Plasmodium.
• After a period of between two
weeks and several months
(occasionally years) spent in
the liver, the malaria
parasites start to multiply
within red blood cells,
• http://www.youtube.com/wa
Life Cycle of Plasmodium
• The parasite's primary
(definitive) hosts are humans
and other vertebrates.
Female mosquitoes of the
Anopheles genus are
secondary hosts and
transmission vectors.
• Young mosquitoes first ingest
the malaria parasite by feeding
on an infected human carrier
and the infected Anopheles
mosquitoes carry Plasmodium
sporozoites in their salivary
• A mosquito becomes infected
when it takes a blood meal from
an infected human
Deaths Caused by Malaria
• It is estimates that
malaria causes 250
million cases of fever
and approximately
one million deaths
• More than all other
infectious disease
Heterozygote Advantage
Having some sickle cells give a resistance
to malaria.
• Because of this, heterozygotes have a
higher fitness than either of the
• This is known as heterozygote
Heterozygote Advantage
• The sickle cell gene may have been brought to
Africa by people migrating from Southern
Arabia and India, or it may have arisen by
mutation directly in East Africa.
• People who inherited one copy of the sickle cell
allele had red blood cell membranes that did
not admit the parasite.
• Carriers had more children and passed the
protective allele to approximately half of them.
Heterozygote Advantage
• Gradually, the frequency of the sickle cell
allele in East Africa rose from 0.1 percent
to a spectacular 45 percent in thirty-five
• Carriers paid the price for this genetic
protection, whenever two produced a
child with sickle cell disease.
Why do harmful Alleles Survive
over time?
• A disease can remain prevalent when
heterozygotes have some other advantage
over individuals who have two copies of the wild
type allele.
• When carriers have advantages that allow a
detrimental allele to persist in a population,
balanced polymorphism is at work.
• This form of polymorphism often entails
heterozygosity for an inherited illness that
protects against an infectious illness.
Awesome animation about
• http://www.youtube.com/watch?v=kp1bZE
• IB Assessment Statement
Outline three outcomes of the sequencing of the complete
human genome.
Copyright Pearson Prentice Hall
Outline three outcomes of the sequencing of the
complete human genome.
Copyright Pearson Prentice Hall
Human Genome Project
• A project set out to sequence the
complete human genome.
• It hoped to determine all the bases A, T,
C, G in the human DNA.
• In 2003, it succeeded.
• Now scientists are trying to figure out
which base sequence represents genes.
Copyright Pearson Prentice Hall
• Human Genome Project:
• It can be thought of as a map showing the
locus of any gene on the 23 pairs of
Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall
• Benefits of the Human Genome Project:
• Find out if people are carrying a disease
causing allele
• Find beneficial molecules which are
produced naturally by healthy people
• Find out which gene controls the synthesis
of a desirable molecule
• Copy the above gene and use t as
instructions to synthesize the molecule in
a laboratory
• Distribute above molecule as a new
Copyright Pearson Prentice Hall
medical treatment
• Human Genome
• It is estimated that
humans consist of
• More the 1500
genes have been
identified that cause
Copyright Pearson Prentice Hall
Copyright Pearson Prentice Hall
Outline three outcomes of the sequencing of the
complete human genome.
Copyright Pearson Prentice Hall
Human Genome Project
• Click on the below website and watch the
INTRODUCTION animation. In your own
words explain what the Human Genome
Project is:
• http://www.genome.gov/25019885
Copyright Pearson Prentice Hall