understanding heredity

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 deleted2. Duplication – an extra copy of the gene is added3. Inversion – a segment of the chromosome is flipped

over4. 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 disorders2. Autosomal dominant disorders3. 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 cellsCystic Fibrosis – thick mucus secretions in lung, pancreas,

liver and intestinesTay-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