Behavioral Genetics - AndersenLab/Genetic-Analysis GitHub Wiki
Behavioral genetics is the study of how genes determine traits such as circadian rhythms, light attraction, and even personality.
Fruit Fly Behavioral Genetics
The first behavioral genetic screen looked for Drosophila mutants that were defective in their time of eclosion (emerging from the pupal stage) and their daily cycle of locomotor activity. These two phenotypes are related to the circadian rhythm of the animal.
About the screen:
- They were looking for mutations on chromosome X
- Attached-X females (XXY) were mated to mutagenized males (XY)
- Progeny that received the (XX) from the mom and (X) from dad are dead
- Progeny that received the (Y) from the mom and the (Y) from the dad are dead
- Progeny that received the (XX) from the mom and the (Y) from the dad are female and do not carry the mutagenized paternal (X) chromosome. These progeny are not studied.
- Progeny that received the (Y) from the mom and the (X) from the dad look male and might carry a mutation on the paternally-inherited X chromosome.
Pop quiz: What are the advantages of doing this cross and screening for mutations on the X chromosome? Hint: think about what we would see in the F1 if the screen was done on an autosome.
This screen resulted in three different mutants that all mapped to the same spot on chromosome X:
- arrhythmic (have an acyclic behavior, i.e. they eclose seemingly randomly throughout the day)
- short (have a shortened cycle, i.e. they eclose every 19 hours instead of every 24 hours)
- long (have a lengthened cycle, i.e. they eclose every 28 hours instead of every 24 hours)
Heterozygotes of each mutant allele were observed to assess dominance:
- arrhythmic looks recessive
- short and long both look dominant to the wild type
Pop quiz:
- How do you tell the difference between recessive and dominant phenotypes conferred by these mutant alleles?
- What does the lecture suggest about the function of each of these mutants?
Because the three mutants fail to complement, they were said to be in the same gene, named period.
Another genetic screen identified a gene on chromosome 2 called timeless that is also involved in the circadian rhythm process.
Mouse behavioral genetics Because mice run on wheels consistently at night, they are an excellent model for understanding the circadian rhythm.
A mutant screen was performed to look for dominant mutations that cause perturbations in nightly running behavior.
Out of 304 mutants screened, 1 was found to have a slightly lengthened circadian rhythm.
Pop quiz: Why did they look for mutants with dominant phenotypes?
This gene, called Clock was mapped to chromosome 5.
These Drosophila and mouse studies resulted in a better understanding of a very conserved mechanism of circadian rhythm:
Neural Circuits When neurons are activated, there is a high influx of calcium. By using indicators of calcium levels, we can watch neurons turn on and off.
You can also turn neurons on at will with channelrhodopsin. This channel is a gated sodium-potassium pump that opens when blue light shines on it, causing an influx of sodium and the neuron to be in the active state.
You can turn neurons off at will with halorhodopsin, a chlorine pump that opens when yellow light is shined on it, causing the neuron to be turned off.
Use these tools to dissect neuronal circuits -- see what happens when you turn each neuron on and off.
Further Resources:
Clock Mutants of Drosophila melanogaster