UNDERSTANDING HEREDITY Part 2
Dec 25, 2015
UNDERSTANDING HEREDITY
Part 2
MUTATIONS
Mutations
• Genes code for proteins• Mistakes in genetic code cause mistakes in the protein
• Mutations are mistakes in genetic code• A point mutation involves one nitrogen base in a codon
• Some point mutations cause no difference in protein produced
• Others point mutations can cause a noticeable or serious effect
Mutations, cont.
Types of Point Mutations:
1. Substitution – one nucleotide is changed to another
Example: CAT GCA CAG GCA2. Insertion – one nucleotide is inserted into a
sequence
Example: CAT GCA CAG TGC A3. Deletion – one nucleotide is deleted from a
sequence
Example: CAT GCA CAG CA
Mutations, cont.
• Substitutions usually affect only one amino acid
• Insertions or deletions can result in a frameshift mutation – they shift the “reading frame” of the bases
• This can change every amino acid that follows the point of mutation
Mutations, cont.
• Chromosomal mutations – involve changes in the number or structure of chromosomes
• Some may change the locations of genes on chromosomes
• Others may change the number of copies of a gene made
Mutations, cont.Types of Chromosomal Mutations:
1. Deletion – an entire gene is deleted
2. Duplication – an extra copy of the gene is added
3. Inversion – a segment of the chromosome is flipped over
4. Translocation – a portion of a chromosome breaks off and reattaches to another chromosome
Mutations,cont.
• Many mutations are neutral – they have little/no effect on the expression of genes or the function of proteins for which they code
• Some mutations can result in the production of defective proteins that disrupt normal biological activities
• Harmful disruptions cause many genetic disorders• Beneficial disruptions can be the source of genetic
variation that allows certain members of a species to be more successful in a changing environment
Mutations, cont.• Polyploidy – condition in which an organism has an extra set of chromosomes
• Occurs during meiosis when the chromosomes fail to separate
• Triploid- 3N• Tetraploid- 4N• In animals: polyploidy is deadly• In plants:benefits – larger, stronger; source of seedless fruitsdrawbacks – cannot be fertilized; have to purchase seed
to make more plants
GENETIC DISORDERS
Genetic Disorders
• Genetic disorder – disease caused by an abnormality in the organism’s DNA
• Single-gene disorders are inherited in Mendelian patterns:
1. Autosomal recessive disorders
2. Autosomal dominant disorders
3. Sex-linked patterns
Genetic Disorders, cont.1. Autosomal Recessive Disorders:• Most human genetic disorders are caused by recessive
alleles on autosomes• This means the individual must inherit two copies of the
recessive allele• Examples: Sickle-cell Disease – red blood cells develop a rigid sickle
shape; blood cells clot and cause oxygen loss to body cells
Cystic Fibrosis – thick mucus secretions in lung, pancreas, liver and intestines
Tay-Sachs Disease – progressive degeneration of all nerve cells starting about 6 months old with death by 4
Genetic Disorders, cont.2. Autosomal Dominant Disorders:• Less common than recessive because they are often
lethal• In most cases, individuals with disorder live long enough
to reproduce• Keeps allele in population• Examples: Huntington’s Disease & Marfan Syndrome
Huntington’s Disease – • degeneration of nerves• affects muscle coordination
• causes mental and emotional decline
• starts in mid-life • most common cause of death is pneumonia; second most common is suicide
Marfan Syndrome -• affects proper growth of connective tissue
• individuals are unusually tall, with long & thin limbs/toes/fingers
• disruption of proper heart function is most serious complication
Genetic Disorders, cont.
3. Sex-Linked Patterns• Females: XX Males: XY• Y chromosome contains the gene, SRY, that codes for development of the testes
• If testes form, other genes guide production of testosterone and fetus develops into a male
• If Y chromosome is absent or SRY gene does not function correctly, fetus develops into a female
Genetic Disorders, cont.• Genes located on sex chromosomes are called sex-linked
genes• Many genes are found on the X chromosome, but not the
Y chromosome• Because there is not an alternate allele on the Y
chromosome, the allele on the X is the one expressed• Sex-linked = X-linked• Examples of X-linked disorders:Color blindness – inability to see some, or all, colors in
the normal wayHemophilia – blood disorder in which blood does not clot
properly (have low to no clotting factor in blood)
Pedigree Chart – Queen Victoria of England (died 1901)
Died: 1945, no children
BIOTECHNOLOGY
Biotechnology
• Biotechnology – use of living organisms to improve the quality of human life
Biotechnology, cont.
• Bacteria are the most commonly used organisms in biotechnology
• This is because their DNA is not surrounded by a nucleus and is easier to manipulate
• Also, manipulated bacteria reproduce rapidly
• Insulin, produced by E.coli bacteria, is the first protein commercially manufactured using this method
Biotechnology, cont.• Human DNA is 99.9% identical• The .1% difference is displayed in fingerprints, inherited
health conditions and appearance• Gel electrophoresis is a process used by scientists to
isolate and study specific proteins• This increases our understanding about how proteins
work and how we can utilize them to a better quality of life