Genetic Changes• Any mistake or change in the DNA sequence

is called a mutation.

• Types of mutations are:

1. point mutation

2. frameshift mutation

3. chromosomal mutation

Point MutationA change in a single base in DNA.

Frameshift Mutations• A single base is added or deleted from

DNA.

• Usually change the amino acid sequence – results in a protein that may not function

properly

Chromosomal Mutations– Changes the number or structure of chromosomes – Few are passed on to the next generation, because

the zygote usually dies.

4 Types of Chromosomal Mutations

• Deletions: loss of all or part of a chromosome• Insertions/Duplication: part of a chromatid

breaks off and attaches to its sister chromatid causing a duplication of genes on the same chromosome

• Inversions: part of a chromosome breaks off and is reinserted backwards (inverted)

• Translocations: part of one chromosome breaks off and reattaches to a different chromosome

Nondisjunction

• The failure of homologous chromosomes to separate properly during meiosis

• Both chromosomes of a homologous pair move to the same pole of the cell.

• One cell will have an extra chromosome, and the other will be missing a chromosome.

• Organisms with extra chromosomes often survive; organisms lacking one or more chromosomes do not.

Causes of Mutations

• Any thing that causes a mutation is called a mutagen.

• Mutations are generally random events and provide variations that enables species to evolve.– Many environmental agents also cause mutations.

• Exposure to X-rays, UV light, radioactive substances, or certain chemicals can cause changes to DNA.

Karyotypes

• A picture taken of stained chromosomes found in a cell during metaphase. – Chromosomal disorders can be identified using a

karyotype.

• The picture is enlarged so the geneticist can cut apart and arrange the chromosome pairs by length, banding pattern, and centromere placement.

• The geneticist can use the karyotype to see if there are too many chromosomes, too few chromosomes, or chromosomal abnormalities.

Trisomy 21, Male Karyotype

Normal Male Karyotype

Genetic Disorders• Hemophilia - Caused by a recessive gene on the X

chromosome. One can bleed to death with small cuts.

• Downs Syndrome - Caused by non-disjunction of the 21st chromosome. 3 – 2lst chromosomes

• Sickle Cell Anemia - red blood cells, normally disc-shaped, become crescent shaped, and get stuck in blood vessels

• Cystic Fibrosis – Recessive disorder, deletion of only 3 bases on chromosome 7, Fluid in lungs, potential respiratory failure

• Tay-Sachs Disorder - autosomal recessive, Central nervous system degrades, ultimately causing death.

• Color Blindness - x-linked recessive, can’t distinguish between red and green

Down’s Syndromeor Trisomy 21

Pedigrees• A diagram, similar to a

family tree, used by geneticists to show genetic relationships within a family.

• Pedigrees can:– Show if a trait is inherited.– Show how a trait is passed

from one generation to the next.

– Determine whether an allele for a trait is dominant or recessive.

Gel Electrophoresis

• DNA Fingerprinting