How fo genotypes work? Why do people look different, and why do people from the same country look more similar?
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It has been a long time since Bio 101 so forgive me if I fuck this up (also, this used to be one of my favorite subjects back in the day so this might get wordy so I’ll start with the tldr).
TLDR (genotype): Your genotype is your genetic makeup, which you get from both of your parents.
TLDR (phenotype): Your phenotype is what genes you show (express) based on which genes are dominant.
TLDR (geographic appearances): When people weren’t moving around a lot back in the dark times before mass transit, a lot of people with similar features (which developed in part due to where they live), were spending generations breeding with each other and passing those similar genes around. For instance, they say that dark skin is more prevalent closer to the equator because of the need for protection from the sun’s rays while lighter skin is common in more northern areas, where the sun isn’t as direct. Now that people are moving around more, genes are being spread which makes us more diverse, and in some cases healthier.
More complicated:
Genotype is the genetic makeup and it contains a set of genes from your mom and your dad (so, two hair genes, two teeth genes, two eye genes, etc). Those pairs combine and express themselves based on dominance. Phenotype is what you actually see. (example: MC1R is the red hair gene, what people see when they look at my red hair is the phenotype).
Dominant (stronger) genes will be the ones you see, and you only need one copy of a dominant gene because it will always squash the recessive gene.
Recessive genes will not be seen because they are too weak to overcome the dominant gene.
However, you have two copies of each gene (one from egg, one from sperm) so if you have two of the same recessive gene, that will be the phenotype (what you see).
Even though you express your dominant genotype, you can still pass on the recessive genotype. Every egg/sperm you make contains either your mother’s or your father’s genes or
more likely, a combination of both. When your body is producing sperm or eggs, you will get bits from both of your parents in each one so you may get eggs/sperm with your mom’s hair genes and eggs/sperm with your dad’s hair genes. Pure chance is what determines which one your kids will get (based on which egg is released and which sperm is fastest/strongest).
Geography: You ever hear those stories about a white couple producing a black baby and the mother insists she didn’t cheat, only to find out that some distant ancestor raped a slave and kept the baby or something similar? If your family is from a predominantly white area for generations, and only one person was black, as time goes on the black will be less likely to show up. You might have had a couple people who were obviously mixed back when the mixing first occurred but as they continued to live and procreate in the predominantly white area, the black genes may just get quietly passed down for generations in the form of recessive genes until some poor women is accused of cheating.
More on the subject:
Your genetic makeup is a combination of half from your mother and half from your father. Likewise, their genetic makeups were combinations from their parents.
Your mother has DNA made up from her father and her mother. Your father has DNA made up from his father and his mother.
Here’s a hypothetical using what I know of my family, regarding hair color
r – the red hair gene. It’s lowercase because red is recessive
B – the brown hair gene. It’s uppercase because it’s dominant to red.
x – unknown gene – we know the phenotype because we see it but we don’t know what the second gene is.
Hypothetically my parents and all 4 of my grandparents had brown hair. So, we know they had the B gene. However, we don’t know what that second gene is because we can’t see it. So, all 4 of them have a Bx for hair color. But, we can figure out more info by looking farther.
I have red hair. My genotype is rr. I know it’s rr because any other combination wouldn’t have me being redheaded because red is recessive to everything else and needs 2 to work. So, looking back at my parents, we know I had to have gotten an r gene from each parent, which means both my brunette parents have Br genes.
So we have:
Mom’s mom: Brown hair (Probably Br because her dad was a redhead)
Mom’s dad: Brown hair (Br or Bx)
Dad’s mom: Brown hair (Br or Bx)
Dad’s dad: Brown hair (Br or Bx)
Mom: Brown hair (Br, passed r to me)
Dad: Brown hair (Br, passed r to me)
Me: red hair (rr)
Let’s go down another generation.
As I said, I am a redhead (rr). My husband is a brunette with redheads in his family history and present so he could be Bx or Br.
Our hypothetical kids: Br (B from him, r from me), xr (x from him, r from me), rr (r from him, r from me). We could also have a kid with each combination leading to a brunette, a redhead, and a blond!
I think I’ll stop now because this could go on forever.
However, back to geography. Go way way back in time when there were far fewer people. You may have had only 10 families in a small town. Since people didn’t move around a lot, it stands to reason that their families had been in the area for a long time and had been intermixing with each other for a long time. Even though they’re not really inbreeding, there is still a limited gene pool simply because everyone there comes from a similar background. But, if a group of travelling merchants from another continent comes along and has some fun, you may end up with some unusual changes in the new generation. The merchants pass through and leave behind some babies that don’t quite look like their family members. Maybe their skin is a bit darker or their hair is a bit curlier. But, they grow up and don’t move and have babies with others from the same area and eventually those unusual traits fall into the background. But, they’re still there, just waiting for the chance to pop up again.
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