Analogies

A deck of cards can illustrate the concept of recombination without having to explain all of the cell processes involved (mitosis, meiosis, etc.). This metaphor contextualizes genetic recombination with an approachable method that could be replicated during the holiday season, or to visitors over the weekend. This approachability encourages people to explore the concept and simulate genetic change throughout generations. This is important in today’s world in which genetic testing unlocks mysteries of heritage and ethnicity. People are perplexed when they discover connections to unfamiliar ancestors, or that their ethnic ratios are not as they’d expect. By understanding recombination, people can interpret the random shuffling their genes endured throughout generations—an ancient mystery being unraveled by genetic testing. These genes, or “hands” they were dealt, are a record of the multiple rounds of recombination, with genes from much older ancestors having been replaced over time by the genes of newer ones.

 

Genetic Recombination: Shuffling Cards

Genetic recombination is like shuffling a deck of cards. Just like any fair card game, the cards (chromosomes) need to be well mixed. Chromosomes are randomly shuffled to ensure each human is different and served with a new hand to have the best odds at the game of life.

 

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It all starts with Mom (red deck) and Dad (black deck). Each card represents an allele: a portion of a chromosome that codes for a specific trait, such as hair color, height, etc. Some of these alleles will be passed on and become traits their child shares with them. For simplicity, let’s see how Mom’s genes are shuffled and readied for fertilization.

 

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Each chromosome comes in a pair, which is represented by the two rows of cards. Each row came from a different parent, represented by their difference in suit (diamonds and hearts). Only half of these cards will appear in her child, who will also get half of Dad’s genes.

 

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Mom’s chromatids cross over and swap cards. The genes shuffle at random, creating a new combination in every cell. Let’s take a look at the egg.

 

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As you can see, the egg (top row) contains only half of the genetic information. Recombination is responsible for the creation of distinct sex cells. This is why siblings look different. Identical twins, however, came from the same union of a sperm and an egg, so they share identical DNA. The bottom row also becomes an egg, but for this example we will be focusing on the top egg.

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Here the Dad’s sperm has similarly been halved and recombined before uniting with the egg. These two distinct halves create a whole, and their child has all the DNA it needs.

 

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These genes do not change once the sperm and egg meet, and constitute their daughter’s genes. While the daughter is still developing in the uterus, her chromosomes recombine to create her own unique eggs. Again, each egg will only contain half of her genes, so only a quarter of each of the parents’ genes will be included in the daughter’s eggs.

 

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Two generations have passed and the only alleles that remain from Mom are the red of diamonds, or cards “9” through “5.” This is only 12.5% of Mom’s original DNA. With every generation, some cards are shuffled and dealt in and others are taken out. Recombination allows each person to be dealt a hand different than the previous game, and allows every human to be different from those before us and those to come.

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Mendelian Versus Non-Mendelian Genetics: Pixelated Computer Screen

The main difference between Mendelian and non-Mendelian genes are the varying levels contribution to their traits. A single Mendelian gene single-handedly codes for a specific trait. An example of this in humans is rare diseases, like cystic fibrosis, which results from the presence of a single gene.

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On the other hand, non-Mendelian genes—many genes with a small effect—determine some trait as a collective. Height, hair, and eye color are all examples of traits that rely on input from hundreds of genes. Think of a computer screen. From afar, the desktop photo just looks like a sunset landscape. Much like eye color, this scale is deceiving. Zoom in on the photo until you can see individual pixels. These pixels are like non-Mendelian genes. They go unnoticed individually, but as a collective, they create a much larger picture.

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Metaphors

These metaphors would be told by someone familiar with biology to a person wanting to understand some aspect of biology. The metaphors below each describe a process in the body.

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Neuron Firing

Your brain works a lot like electrical wiring. Signals, or action potentials, are sent down your neurons. They are insulated by what is called the myelin sheath, much like how wire is insulated with a non-conductive material. This insulation maintains the action potential inside the neuron and travelling to its destination.

 

Antibodies are Key

Antibodies work like a key. They are produced with a distinct shape that can only fit on the docking site of a harmful antigen they were made to eliminate. This lock and key mechanism is how antibodies locate and destroy antigens in your body.

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Schema

Mass Extinctions: Blackouts

Mass extinctions were like city blackouts, except that they lasted for thousands of years. Blackouts bring life to a halt in cities, much like mass extinctions. The city becomes unfamiliar, everything is dark, food spoils, and people even die in car accidents. Imagine all five mass extinctions throughout history were represented by five major power outages within just one year.

 

Midnight, New Years Day

The ball is about to drop, and the crowd finally counts down to midnight—and the lights go out. Heaters stop working, and people are cold and disoriented 35 minutes until the power comes back when life returns to the city.

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March 1st

This time, the power is out for 25 minutes.

 

May 23rd

Today, fortunately the power is only out for 5 minutes before life returns to normal.

 

June 28th

The disorientation only lasts 50 seconds.

 

October 15th

Just one last minute passes in the dark.

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Permian Mass Extinctions: 96% of Life Lost

Imagine that 96% of the human population disappeared. All that would remain is 32 million people—the current population of Iraq. The rest of the world no longer contains the hustle and bustle of life as we know it. The Permian Mass Extinction lasted for about 100,000 years before life began to thrive again.