During our second session at Finkl, we explored the role of genetics in engendering the unique combinations of attributes that comprise us. When asked if anyone knew what a gene was, many of the girls shook their heads. Some said they had heard of it but didn’t understand what it meant.
We began our journey into the world of genetics by analyzing the process that takes us from the single cell from which we are created to the trillion cells that compose each of us. Your cells, the girls learned, are constantly dividing through a process called mitosis, a process that involves the replication of DNA and eventual creation of two cells from one. We illustrated this by lining up. I gave each student a strip of paper with a color on it. The first line represented one set of chromosomes, and the second, paired evenly with the first, symbolized the copies. During prophase, the initial stage, the girls learned that DNA is copied, that the chromosomes in the cell — the organized structures containing DNA — normally hard to distinguish in the cell’s resting state, condense and become visible. The girls then lined up next to their “copy,” enacting the condensing of chromosomes that occurs during metaphase, the next step of mitosis. The lines moved a foot apart, mimicking the movement of the chromosomes to opposite sides of the cell during anaphase. Finally, during telophase and cytokinesis, the chromosomes arrive at opposite ends of the cell, and the cell divides, forming two identical daughter cells, which the girls depicted by moving to opposite sides of the classroom.
But if mitosis creates two identical daughter cells, how do we end up the unique gene combinations that make up each of us? The girls shook their heads. They didn’t know. It seemed odd.
To make the zygote, the single cell from which we come, the girls learned, the body uses a process called meiosis to create haploid cells — that is, cells with only one set of chromosomes. Our typical cells are diploid and have two sets of chromosomes. The mom donates one haploid cell, and the dad donates another to create a zygote, which itself is subsequently diploid. Meiosis enables the creation of haploid cells and therefore necessitates a process called crossing over, or gene recombination, a process the students illustrated by again lining up next to their “copies,” ripping their strips of paper and exchanging a piece with their neighbor, thereby creating sets of chromosomes that looked nothing like their originals. They then went through the process of dividing into four different groups, copying meiosis’ production of four daughter cells.
Melina and Ninel exchanged looks. The lesson was informative, sure, but maybe a little boring?
So why, I asked them, is the idea of meiosis so important?
“Because that’s how we’re different from each other?” Kathy offered.
Exactly! It has to do with the idea that different gene combinations can result and create a zygote with features derived from both parents.
To illustrate how influential different traits can be, and how scientists can determine the likelihood of a child inheriting certain traits from his or her parents, we examined the role of dominant and recessive alleles through Punnett squares and dragons. Yes, that’s right — dragons.
We created a scenario in which we had fire-breathing dragons and non-fire-breathing dragons, winged dragons and wingless dragons. Fire breathing and wings were dominant traits, which meant even if the dragon had genes for either fire breathing or wings, said dragon would express those genes, regardless of other genes. To be wingless or not fire breathing, however, the dragon would need both genes to have those recessive traits. This, the girls learned, is the difference between a person’s genotype — the genes s(he) has — and the phenotype — the expression of those genes.
The girls loved drawing Punnett squares with partners to see what baby dragons would result from their crosses, seeing the diversity stemming from gene recombination.
When we finally journaled, Denise shared that she “used to think genes just meant the jeans you wear,” but now she knows that “genes create who you are.” Many of the students reiterated that sentiment, with Kathy adding that now she knows “that you get genes from your parents and they decide what you look like and that crossing over means you could look a lot like one parent and not as much like the other.” Lesly interjected, “Like when one parent has blue eyes and one has brown eyes, you might have brown eyes because brown is dominant.”
The students like learning the underlying — if basic — principles behind their genetic makeup and can’t wait for the next lesson!