GEL ELECTROPHORESIS

What does gel electrophoresis do

Separates DNA samples by length

Explain the process of gel electrophoresis

• DNA samples are loaded into wells in an agarose gel.

• Gel is immersed in buffer solution to help carry current. Current is supplied.

• DNA migrates to the positive electrode. Larger DNA samples face more resistance from the gel, so move more slowly. DNA fragments are separated into bands.

• Current is turned off. Bands are dyed with ethidium bromide to enhance visibility.

what is the standard ladder

a mixture containing DNA fragments of known lengths, from which, by comparison, the length of unknown fragments can be estimated.

What property of DNA makes gel electrophoresis possible

• It is negatively charged

• Agarose gel resistance makes different sizes of DNA fragments travel different distances.

Factors that affect how far DNA travels

• Voltage (positive correlation)

• Gel density (negative correlation)

• Buffer concentration (more ions = positive correlation)

• Time (positive correlation)

Safety precautions for gel electrophoresis

• do not allow direct contact with ethidium bromide

• do not look directly into lamp

• do not directly expose yourself to current

explain why the standard ladder is necessary in order to determine the results of gel electrophoresis accurately

• DNA strands do not move a fixed position as the voltage, gel composition, and time cause variance.

• Having bands of known length allow comparative results to the bands under examination.

What does STR stand for

→Short Tandem Repeats

What is a STR

Stretches of DNA that are repetitive

Two main properties of STRs

• STRs vary in length between individuals

• We know where they are in the genome