GENETICS
A gene is a heritable factor that controls or influences a specific characteristic.
CHROMOSOME
(made of DNA & protein)
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contains genes
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ALLELES are different versions of the same gene
p
q
11p15.5
Refer to the p arm on the 11th chromosome, location 15, and allele no. 5
GENE LOCUS - Specific position of a gene on a chromosome.
GENE MUTATIONS - A permanent inheritable change in the base sequence of DNA.
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- If mutation is in intron, no change (non-coding region)
- If mutation is in exon, change! (coding region)
"FRAME SHIFT MUTATION"
changes sequences
BASE-SUBSTITUTION MUTATION (ADDITION/DELETION/SUBSTITUTION)
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Silent Mutation - The change in base sequence has no effect on amino acids produced.
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Missense Mutation - Causes one different amino acid to be produced. --> sickle cell!
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Nonsense Mutation - A STOP codon is produced, polypeptide is shortened. --> cystic fibrosis!
- Malaria is a parasitic disease carried by Anapheles mosquito
caused by plasmodium cell
invades normal red blood cells
- Plasmodium invades RBCs and causes them to lyse
- SYMPTOMS: Fever, shivering, vommiting, anaemia, death --> kidney failure/severe anaemia
- Malaria cannot infect SICKLE CELLS! People with sickle cell trait are resistant to the disease. Sickle cell is more prevalent in places with malaria.
SICKLE CELL DISEASE
- A single base substitution leads to the production of valine instead of glutamine.
- Abnormal red blood cells are produced (RBCs). Sickle shaped. Binds with less O2.
- People with one faulty copy of the gene produce some abnormal Hb, but are fine. People with two faulty copies of the gene produce all abnormal Hb, which is dangerous!
CCT GAG GAG | CCT GTG GAG
GGA CTC CTC | GGA CAC CTC
Pro Glu.ac Glu.ac Pro Val Glu.ac
Prokaryotes have two types of DNA:
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1. Single chromosome (responsible for normal life processes)
2. Plasmids (Naked DNA, not associated with histone proteins, not responsible for normal life processes, contain survival characteristics, can be passed between prokaryotes, can be incorporated into nucleoid chromosome).
Autoradiography - John Cairns
HOW ARE CHROMOSOMES IDENTIFIED?
1. Size
2. Bonding Pattern
3. Centromere position
Producing images of DNA molecules from Escherichia Coli (E.Coli)
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E. Coli is grown with thymidine containing a radioactive isotope of hydrogen (DNA was labelled)
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E.Coli cells were broken open by enzymes to release all contents
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Cell contents were applied to a photographic emulsion and placed in the dark (two months)
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The radioactive isotope reacted with the emulsion
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Dark areas on the photographic emulsion indicated presence of DNA
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E. Coli possesses a single circular chromosome.
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Cairns's images also provided evidence to support the theory of semi-conservative replication
DOWN SYNDROME (x3 21 chromsomes)
- Risk of child having a trisomy such as Down Syndrome increases greatly in older mothers.
- Prenatal tests
Nuchal translucency scan: Between 11th and 13th week, build up of nuchal fluid near neck of fetus. Large amounts may indicate Down Syndrome.
Amniocentesis: Sample of amniotic fluid taken (till 16th week, with 1% chance of miscarriage)
Chronic Villus Sampling: Sample taken from placenta (till 11th week, 2% chance of miscarriage)
As no. of weeks increases, the chance of miscarriage also increases from these procedures.
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MENDAL'S LAWS!
1. Law of dominance
2. Law of segregation
3. Law of independent assortment
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*Only applies to non linked genes.
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Types of genes
1. Linked genes
2. Non-linked genes
3. Sex-linked genes
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PHENYLKETONURIA (PKU)
- A metabolic disease in which your body cannot process phenyl (metabolic substance).
- Missence mutation in the gene that produces tyrosine in the body; making it build (anything in large amounts is toxic)
- Build up results in brain developmental problems and seizures.
- Progressive, so must be diagnosed and treated early.
- Dairy, breast milk, meats, nuts, and aspartame must be avoided (rich in phenylalanine)
- Recessive homozygous disease.
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pp x PP
Pp x Pp
***NOTE! Punnet squares, hereditary diagrams, & basic concepts done in detail in presentations.
P
p
p
Pp
Pp
P
p
P
p
Pp
PP
pp
Pp
Pp
Pp
P - dominant
p - recessive
PP - homozygous dominant
Pp - heterozygous (carrier)
pp - homozygous recessive (affected)
P
All heterozygous, no offspring gets disease. All carriers.
1:4 chance of getting disease.
HEMOPHILIA
- Sex linked inheritance, blood does not clot
- Requires globular proteins called clotting factor. A recessive X-linked (female) mutation in hemophiliacs results in one or these factors not being produced. Therefore the clotting response to injury does not work & the patient can bleed to death.
X
H
h
X
Y
X
h
X
X
H
X
X
h
h
X
Y
X
Y
X
X
X X
X X
X Y
H
H
H
h
h
h
h
h
h
X
Y
X
X
X X
X X
H
H
H
h
h
h
h
h
h
X Y
X Y
X Y
- All females are carriers
- All males are affected
1:1 ratio
- 1 carrier female, 1 unaffected male
- 1 affected female and male
X
h
h
X
Y
H
X
Affected female
Unaffected male
X
h
Y
Affected male
X
h
H
X
Carrier female
X
h
Recessive
X
H
Dominant