1) A gene is a length of DNA that codes for a specific characteristic and is located at a specific position on a chromosome. 2) Alleles are different forms of the same gene that differ by one or a few DNA bases. Mutations introduce new alleles. 3) The human genome project determined the entire DNA sequence of human genes, consisting of about 23,000 protein-coding genes. Understanding the genome provides benefits like more precise medical treatments.

1. 3.1 Genes
• Essential idea: Every living organism inherits
a blueprint for life from its parents.
http://pixabay.com/static/uploads/photo/2014/05/11/14/25/elephants-341981_640.jpg

2. Understandings
Statement Guidance
3.1.U1
A gene is a heritable factor that consists of a length of DNA and influences
a specific characteristic
3.1.U2 A gene occupies a specific position on a chromosome.
3.1.U3 The various specific forms of a gene are alleles.
3.1.U4 Alleles differ from each other by one or only a few bases.
3.1.U5
New alleles are formed by mutation. [Deletions, insertions and frame shift
mutations do not need to be included.]
3.1 U6 The genome is the whole of the genetic information of an organism.
3.1 U7
The entire base sequence of human genes was sequenced in the Human
Genome Project.

3. Applications and Skills
Statement Guidance
3.1.A1
The causes of sickle cell anemia, including a base substitution mutation, a change to the base
sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in
hemoglobin. [Students should be able to recall one specific base substitution that causes glutamic
acid to be substituted by valine as the sixth amino acid in the hemoglobin polypeptide.]
3.1.A2
Comparison of the number of genes in humans with other species. [The number of genes in a
species should not be referred to as genome size as this term is used for the total amount of DNA.
At least one plant and one bacterium should be included in the comparison and at least one
species with more genes and one with fewer genes than a human.]
3.1.S1
Use of a database to determine differences in the base sequence of a gene in two species. [The
Genbank® database can be used to search for DNA base sequences. The cytochrome C gene
sequence is available for many different organisms and is of particular interest because of its use
in reclassifying organisms into three domains.]

4. 3.1.U1 A gene is a heritable factor that consists of a
length of DNA and influences a specific characteristic
Eukaryotic Chromosomes
• The Photograph shows a
human chromosome. The
picture show two
chromatids joined at the
centromere.Each
Eukaryotic chromosomes is
composed of
•DNA
•Protein
(Histones)

5. Chromosome
Histones
DNA double helix
3.1 U.1 A gene is a heritable factor that consists of a
length of DNA and influences a specific characteristic
Chromosome is a length of DNA with associated proteins (histones).

6. Homologous Pair of Chromosomes:
One Comes From Each Parent
•Gene loci is the position of the gene on a chromosome. Alleles have the same
gene loci.

7. 3.1 U.2 A gene occupies a specific position on a
chromosome.
http://www.daviddarlin
g.info/images/gene.jpg
•Gene is a heritable factor that controls a specific
characteristic. There are over 20,000 genes that make up a
human. One gene codes for one polypeptide.

8. Allele is one specific
form of a gene, differing
from other alleles by
one or a few bases only
and occupying the same
gene locus as other
alleles of the gene.
3.1 U.3 The various specific forms of a gene are alleles.

9. 3.1 U.4 Alleles differ from each other by one or only a few
bases.
This may cause:
•Change in the base sequence of the gene
•Change in the mRNA made in transcription
•Change in the amino acids sequence / primary structure of the protein
•Change in the secondary/ tertiary or quaternary structure of the
protein
•Change the shape of the protein
•Change the function of the protein.
http://evolution.berkeley.edu/evolibrary/images/interviews/pax_mouse_fly.gif

10. Examples of the mutations to the gene
Deletion
Duplication
Inversion
Translocation
3.1 U.5 New alleles are formed by mutation. [Deletions, insertions and
frameshift mutations do not need to be included.]
http://www.goldiesroom.org/Multimedia/Bio_Images/19%20Applie
d%20Genetics/05%20Chromosome%20Mutations.jpg

11. 3.1 U.6 The genome is the whole of the genetic information
of an organism.
Allows for:
• Physical mapping of chromosomes
• Used to screen for genetic diseases
• Lead to a better understanding of genetic diseases.
• May lead to the development of better drugs to fight diseases.
• Maybe be used for comparison of genomes with other species.

12. 3.1 U.6 The genome is the whole of the genetic information
of an organism.
Genome Size and Number of Genes

13. Chromosome 16
3.1 U.6 The genome is the whole of the genetic information
of an organism.
http://physrev.physiology.org/content/physrev/91/1/151/F11.large.jpg

14. 3.1 U.6 The genome is the whole of the genetic information
of an organism.
Advantages from the project
Advantage 1
• Screening can also be done for
adults, to see if they may be
carriers of potential genetic
conditions. Certain Jewish and
Canadian populations regularly
obtain voluntary screening for Tay-
Sachs disease, a known child-killer.
This information has been used to
help make decisions about future
marriage partners.
Advantage 2
Perhaps the greatest benefit will come
from what is called gene-based
therapy. Understanding the
molecular workings of genes and
the proteins they encode will lead
to more precise drug treatments.
The more precise the drug
treatment, the fewer and milder
will be the side effects.

15. 3.1 U.7 The entire base sequence of human genes was
sequenced in the Human Genome Project.
http://www.bioscience.heacademy.ac.uk/imagebank/search/Fullimage.aspx?IDvalues=6513
• The project began in 1990 and was completed in 2003.
• It is now know which base sequences are protein coded genes
• There about 23,000 genes
• Much of the genome is highly repetitive base sequences that are not
translated in
proteins originally called “junk DNA”. Now referred to as satellite
DNA

16. 3.1 A.1 The causes of sickle cell anemia, including a base substitution mutation, a change to the
base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in
hemoglobin. [Students should be able to recall one specific base substitution that causes
glutamic acid to be substituted by valine as the sixth amino acid in the hemoglobin
polypeptide.]

17. 3.1 A.1 The causes of sickle cell anemia
The Disease:
•Sickle cell anemia is an inherited disorder
that affects hemoglobin, a protein that
enables red blood cells to carry oxygen
to all parts of the body.
•The disorder produces abnormal
hemoglobin, which along with the
abnormalities of the cells membrane
cause damage from be trapped and
freed in the capillaries. This shortens
the blood cells life to as little as 4 days.
Disease Symptoms:
•chronic anemia,
•acute chest syndrome,
•stroke,
•spleen and renal dysfunction,
•pain crises and susceptibility to bacterial
infections, particularly in children.
•Sickle cell disease is also associated with
significant mortality.

18. 3.1 A.1 The causes of sickle cell anemia
•The HBA gene carries the
instructions for the manufacture
of a protein that is a component
of hemoglobin.
•Hemoglobin is the protein
containing a sequence GAG
which codes for the amino acid
glutamic acid.
•In a base substitution mutation of
Hemoglobin proteins in Sickle
Cell Anemia. GAG has been
changed into GTG which codes
for the amino acid valine. It is
given the symbol HBs for the
gene.
http://upload.wikimedia.org/wikipedia/commons/a/ac/Sickle_cell_01.jpg

19. Alleles, genotypes and Phenotypes of Sickle Cell:
HbA Normal allele producing normal protein using the amino acid
glutamic acid
Hbs Sickle allele which is the abnormal mutation of the normal
allele. Is produced using the replacement amino acid valine.
3.1 A.1 The causes of sickle cell anemia
http://www.zo.utexas.edu/faculty/sjasper/images/17.23.gif

21. 3.1.A2 Comparison of the number of genes in humans with other species. [The
number of genes in a species should not be referred to as genome size as this term is
used for the total amount of DNA. At least one plant and one bacterium should be
included in the comparison and at least one species with more genes and one with
fewer genes than a human.]