IS IT GOING TO HAPPEN OR WHAT?!...
I have established in another post that the parents' alleles combination for each trait determines the potential for what each child will inherit from the biological parents. Every child begins with a "clean slate" of genetic alleles they may inherit. For this reason, each child, even to the same biological parents can look somewhat or very different than their siblings.
I am going to use four circles to represent the four alleles of the parents (two for mom and two for dad) and two circles for their child in every pregnancy. Each time, I will analyze the parents' alleles and the possible combinations of alleles that the child of the current pregnancy will inherit, as well as the potential for a certain trait to be genetically expressed.
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Before I begin, I would like to explain how the scenarios will be presented: every time a circle if of its own color (different than another circle's color) it represents a different variation of a gene (a different allele). If two circles are the same color, they represent the same alleles for the same trait and less genetic variation. Let's begin with the easiest genetic scenario possible:
Let's imagine the each one of the circles above represents an allele of one of the parents for eye color or hair color. The two on the left for mom's and the two on the right for dad's. It is clear that their next child will inherit only brown eyes or brown hair, depending on what trait these alleles are for. It also means that any child of these two biological parents will only inherit brown eyes and/or hair. All the siblings to the same biological parents with this set of four alleles will have the same color eyes and hair.
In the case of the set of alleles above, let's say for eye color, three alleles code for brown eyes, while one of dad's alleles code for blue eyes. The child might inherit the genetic alleles only for brown eyes, or the genetic alleles for both brown and blue eyes. Thus, while the natural chances for the expression of brown eyes (meaning that the child will have brown eyes) are 75%, brown is a more dominant genetic trait compared to blue, increasing the actual chances of the child having brown eyes to an estimated 80-85% and reducing the child's chances of blue eyes to an estimated 15-20%. Every child to these biological parents "resets" the odds.
In the case of the set of alleles above, let's say for eye color, mom' s two alleles code for brown eyes, while dad's two alleles code for blue eyes. The child will definitely inherit the genetic alleles for both brown eyes and blue eyes (brown only from mom and blue only from dad). Thus, while the natural chances for the expression of brown eyes (meaning that the child will have brown eyes) as 50%, brown is a more dominant genetic trait compared to blue, increasing the actual chances of the child having brown eyes to an estimated 55-60% and reducing the child's chances of blue eyes to an estimated 40-45% compared to the natural 50% chances. Every child to these biological parents "resets" the odds.
In the case of the set of alleles above, let's say for eye color, mom' s two alleles code for brown and blue eyes, while dad's two alleles code for brown and blue eyes. There are three possible allele combinations that the child might inherit. 1) The child inherits only brown alleles and thus will definitely have brown eyes; 2) The child inherits one allele for brown eyes and one allele for blue eyes, thus having a 55-60% chance of having brown eyes; 3) The child inherits only blue alleles and thus will definitely have blue eye. Every child to these biological parents "resets" the odds.
In the case of the set of alleles above, let's say for eye color, mom' s two alleles code for brown and blue eyes, while dad's two alleles code only for blue eyes. There are two possible allele combinations that the child might inherit. 1) The child inherits only blue alleles and thus will definitely have blue eyes; 2) The child inherits one allele for brown eyes and one allele for blue eyes, thus having a 55-60% chance of having brown eyes. Every child to these biological parents "resets" the odds.
In the case of the set of alleles above, let's say for eye color, mom' s two alleles code for blue eyes, while dad's two alleles code only for blue eyes. It is clear that their next child will inherit only blue eyes. It also means that any child of these two biological parents will only inherit blue eyes. All the siblings to the same biological parents with this set of four alleles will have the same color eyes.
Next, let's bring into the mix one more eye color possibility and then one more. Let's "bring in" to the scenario the allele for green eyes and analyze all the possible combinations and chances of inheritance.
In the case of the set of alleles above, let's say for eye color, mom' s two alleles code for brown eyes, while dad's two alleles code for blue and green eyes. There are two possible allele combinations that the child might inherit. 1) The child inherits brown and blue alleles and thus having a 55-60% chance of having brown eyes; 2) The child inherits brown and green alleles and thus having a 55-60% chance of having brown eyes. Every child to these biological parents "resets" the odds.
In the case of the set of alleles above, let's say for eye color, mom' s two alleles code for brown and green eyes, while dad's two alleles code for green and blue eyes. There are four possible allele combinations that the child might inherit. 1) The child inherits only green alleles and thus will definitely have green eyes; 2) The child inherits one allele for brown eyes and one allele for blue eyes, thus having a 55-60% chance of having brown eyes; 3) The child inherits one allele for brown eyes and one allele for green eyes, thus having a 55-60% chance of having brown eyes; 4) The child inherits one allele for green eyes and one allele for blue eyes, thus having a 50% chance of having blue or green eyes since blue and green are colors that do not dominant each other (they are equally dominant). Every child to these biological parents "resets" the odds.
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Time for one last analysis, and "bringing in" another eye color. I will use black yet it could also be grey eyes for the same example. Both black and grey eyes are extremely rare and recessive (not dominant) colors when related to eye color (not the same case for hair color).
In the case of the set of alleles above, let's say for eye color, mom' s two alleles code for brown and black eyes, while dad's two alleles code for green and blue eyes. There are four possible allele combinations that the child might inherit. 1) The child inherits alleles for black and blue eyes, and thus having a 75-80% chance of having blue eyes; 2) The child inherits alleles for black and green eyes, and thus having a 75-80% chance of having green eyes; 3) The child inherits one allele for brown eyes and one allele for green eyes, thus having a 55-60% chance of having brown eyes; 4) The child inherits one allele for brown eyes and one allele for blue eyes, thus having a 55-60% chance of having brown eyes. Every child to these biological parents "resets" the odds.
Last, some traits are very genetically unstable. some traits are moderately genetically unstable, and some traits are very genetically stable. Genetic traits that are unstable tend to switch between the genetic variations that the person has (especially up to the age of 3 years), while stable genetic traits do not tend to switch between the genetic variations that the person has. Moderately unstable or moderately stable genetic traits could change between the genetic variations that the person has, with a probability of changing of 25% - 75%.
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