Honey Bee Genetics
The posts have been slow to rise lately, because I’ve been busy with things:
- I’m writing a paper.
- I’m still taking that Science Journalism course, and working on a final ~3,000 word piece, which I’ll put up–here or elsewhere–when I’m done. I can tell you it’s about some brilliant research coming from the lab of Dianne Newman, an MIT Professor.
- As usual, I’m banging drums in an MIT jazz combo. This term we’re playing, among others, the James Brown song “Mother Popcorn,” and it’s sooo funky.
- Other miscellaneous debris.
To tide readers over until a more steady stream of original content appears, I am posting something I wrote three years ago, when I was a wet behind the ears first year graduate student. The Department of Biology has a wonderful class, only for the first year grad students, called “Methods and Logic in Molecular Biology” (colloquially known as “seven-fifty” or “Methods”), an intense paper reading course led by several faculty. (Actually, eventually I should probably write some posts about these classes for potential students or others who are interested?)
Anyhow, our section for Methods became somewhat tight, and occasionally we exchanged emails about the current week’s assigned papers. Around 2am on the day of the last class of the semester, I sent the following email to my section. Clearly I was high on something–not a controlled substance; possibly a couple beers; likely joy at almost being done with the class/semester; as likely rebellion against being told what to read, instead choosing to read what I wanted to. Most of my classmates had already exhibited in spades dysfunctional behavior, it was my turn. I still think it’s a stimulating read:
On the eve of our last class, instead of re-reading the papers I did some Internet research into the fascinating area of honeybee genetics. Topic is more interesting than heat maps or MALDI experiments. Some things I found:
In a bee colony, there are three types of bees: few female queens, hundreds of male drones, and thousands of female workers. Females are diploid and males are haploid. Females develop from fertilized eggs. Haploid male drones develop from unfertilized eggs, and therefore they have no father! Sex determination is made at a single locus, the csd gene, of which at least 19 alleles are known. It seems that all alleles can be found in males and females. It was also shown that once activated, csd remains active throughout development. RNAi inactivation of csd causes diploid female eggs to develop male gonads, but does not affect haploid male egg sexual development. Therefore it has been hypothesized that 2 different alleles of csd somehow result in two protein products that can interact together to direct a specific step in the sex determination pathway towards female development. Hemizygous csd eggs cannot make this product, and thus the default state is male.
Female queen and worker bees develop from queen bee eggs fertilized by drone sperm. Females must be heterozygotes for csd alleles to survive. Diploid flies homozygous for a csd allele develop into sterile males, but soon after these larvae hatch from the comb, they are selectively removed and destroyed by worker bees (not sure how workers can recognize these larvae). (This also makes it difficult to develop inbreed stocks of honey bees, colonies die out quickly due to loss of csd homozygotes.) Since both queens and worker females come from fertilized eggs, what distinguishes them is that between larvae and pupa stages, queens receive a hormonal mixture called the “royal jelly”, whereas workers arise from larvae that have been denied this. Workers are sterile because they don’t develop ovarioles, and only live a few weeks. Queens usually mate once in their life and then live for years.
Queen bees must mate with many drones at one time early in there lifetime, and must do it 50-100 meters in the air and kilometers from their colony! (This makes it difficult for bee breeders to maintain isogenic stocks of bees, an intensely studied research problem in bee genetics.) The drones die after mating, and the queen returns to hive and doesn’t need to mate again. She will produce thousands of offspring from eggs fertilized from perhaps 5-15 drones. From an evolutionary perspective, the fact that she usually mates with multiple partners once early in life, and far from the hive prevents her mating with her own son, reducing the chances of producing half inviable progeny homozygous for csd allele, (which means fewer worker bees to support the colony). Pretty cool, huh.
Oh yeah, consider this my contribution to Thursday’s discussion.
Sorry, but I can’t remember my references.