A Dance of Genes

Hope everyone had a lovely Mother’s Day and showed their mothers and motherly guardians how much they appreciate their hard work. We had scones, worked on a puzzle and watched Guillermo del Toro’s best Mother’s day film, Mama.

Here comes Mama.

Speaking of Mama/mamas, I still owe a post or two on additional exceptions to Mendelian inheritance. These last exceptions include epistasis, mitochondrial inheritance, genomic imprinting and triplet repeat extension.

When one gene is dependent on another for expression, we call that epistasis and the best example is color expression in hair. Because I can, we’ll use Danaerys Targaryen’s magnificent silvery mane as an example.

Maybe she’s born with it, maybe it’s epistasis…Actually, yeah, she’s born with it.

While Dany’s phenotype may be white hair, her genotype for hair color could be a completely different color. She could even be homozygous dominant for black hair, BB. Again, I’m using a simplified version of hair genetics, but Dany’s fireproof and owns dragons, I think I can pretend her hair genetics work like those of mice for the time being. OK, so now she’s genetically black haired. However! She has a separate set of genes that determine whether or not that hair color is expressed; C for color, c for no color. Since Dany does not have black hair, we can safely infer her genotype is BBcc. Without the allele for color expression, Dany’s hypothetical raven waves are in lockdown.

Mitochondrial inheritance is also called maternal inheritance and refers to a set of genes that are always and entirely inherited from the mother. Why? Because I said so. Actually, because the egg is the only gamete (sex cell) to contribute organelles. Sperm have no organelles, just some egg excavation tools and DNA. Eggs, on the other hand, have organelles besides the nucleus and one organelle in particular possesses its own set of DNA: the mitochondria. These are not junk genes, either, mitochondrial DNA includes genes involving cellular respiration and metabolism. Problems with these are rare, but very serious.

The last one did not have any Game of Thrones references but bear with me! It’s Monday and I’m sleepy and y’all don’t pay me, dammit. Geez, I work and I slave…

Source

-. 2010. GRE Subject Test: Biology 5th Ed. Kaplan, New York.

Sounds Good to Me

My back hurts from buzzing around work today like a demented hummingbird on steroids, so I was tempted to talk about neurotransmitters and nerves in signaling pain, but rather than wallow in self-pity, I will talk about ears. Also I don’t have my physiology book.

The part of your ear that you can see is only the tip of the iceberg. Except this one would sink cruise ships. Anyway, your pinna (the visible bit) acts like a satellite dish to improve reception of sound waves. What you learn in elementary and middle school science is that beyond the pinna is the auditory canal, which leads to the eardrum, and through which sound is transmitted. But the sound doesn’t just hit the drum and transmit to the brain like signals through a telephone wire. Your reception would be terrible if the malleus, incus and stapes (three bones of the inner ear) did not amplify the signal and send it through the oval window to the cochlea. Within the fluid-filled cochlea is the organ of Corti, this is covered in hair cells (really they’re cells with hair-like projections, not actual hair…even though that’s funny to imagine) which respond to sound vibrations transmitted through the fluid. The cochlea is curled up and looks sort of like a snail. Different regions of the “shell” of this head snail respond to different kinds of sound, which is easier to imagine if you uncurl the shell. At the far end, the hair cells respond to deep sounds while the near end responds to high-pitched sounds. So Barry White registers in the center of the cochlea/snail shell’s spiral and the Chipmunks register at the outermost end. Of course I would prefer not to register the Chipmunks at all but until they stop showing reruns of those damn movies on TV, I’ll have to endure the previews every so often. Anyway! If you want a visual of the organ of Corti working, here’s a pretty fun video: https://www.youtube.com/watch?v=dyenMluFaUw

Cool note: hair cells will “fine tune” the sound so that the signal is actually clearer than when the sound waves first hit your pinna. As you age or go to too many rock concerts (like my physio professor), the hair cells become damaged and the sound you perceive will be fuzzy. Ironic, considering the hair cells are getting less hairy when this happens.

 

Source

-. 2010. GRE Subject Test: Biology 5th Ed. Kaplan, New York.