Hooray, time to learn more about genetics!

_Elsa_

“Wow are you guys eager to learn more about DNA?” asks Mr. James. “Let’s do the roll call first. Ok, now let’s get down to the good stuff!” 

‘Chromosomes: Packages of DNA - Genes are packaged into tightly wound lengths of DNA called chromosomes. Humans have 23 pairs of chromosomes. Sex chromosomes, identified as X or Y, determine whether a person is male or female. Each chromosome can be identified by its size and shape under a microscope. Each has a specific set of genes that is the same from person to person. One copy of each chromosome in a pair is inherited from each parent, which means that you inherit one copy of each gene from your mother and one copy from your father. Each chromosome has a centromere at its center, which is a small structure that divides the chromosomes into two parts (see figure 2). Each part is called an arm. Genes are located on the arms of the chromosomes. Chromosomes have caps on each arm called telomeres, which help to protect the chromosomes. As you get older, your telomere caps get shorter and shorter and are less able to protect your chromosomes from getting damaged - Figure 2. 

Genes: Coding for Proteins and Traits - Genes are small segments of DNA that have different functions. Many, but not all, genes make the proteins that our bodies need to function. You have two copies of each gene, one on each chromosome in a pair. Genes that code for proteins come in different versions called alleles. Alleles of a gene have differences in the precise DNA sequence. A common example of this is eye color. We each have the same genes for eye color, but different allele combinations within those genes result in different eye colors. 

Traits: What Make Your DNA Unique - Traits are your observable characteristics. Many physical traits are genetic. Genetic differences give our bodies information that result in traits that differ from person to person. We can also use genetic information to determine what inherited traits you may have.

A difference from the expected sequence of a gene is called a variant or mutation. Variants can be inherited from your parents, or they can happen spontaneously. All of us have variants, but not all variants are harmful. Variants that are harmful can cause or increase our risk for certain diseases.

Figure 3 shows a DNA variant where a thymine is replaced with a cytosine. This can cause the gene to produce a different protein that may not function properly.’ (Info here)

‘It is true that identical twins share their DNA code with each other. This is because identical twins were formed from the exact same sperm and egg from their father and mother. (In contrast, fraternal twins are formed from two different sperm and two different eggs.) Usually, the egg and sperm come together and create an embryo, which eventually grows into a human baby. However, in the case of identical twins, early in development, this embryo divides into two. This creates two babies rather than one.

While the two babies share the same DNA code, there is more to our genetics than just that. During development in the womb and after birth, our surroundings, exposures, and nutrition influence how our genes are expressed and how our bodies and minds develop. For example, two identical twins may have the same genes for height, but if one twin does not receive the same amount of nutrients while in the womb, it may be shorter than the other twin. We know also that there are some changes to our genes that can happen during the embryonic period or during development. While this rarely happens, it makes it so that one identical twin may have a genetic condition, while the other twin does not. Our genetic code is a very large part of our genetic makeup, but there are other factors, genetic and environmental, that make us unique!’ (Info here)

The school bell rings to let the students know that class is over and it’s time to get on their busses and go home. All the students have been so engrossed in this DNA conversation and they are a bit disappointed that they can’t learn more. Mr. James lets them know that there is a continuation when this semester ends and the next semester begins. He lets them know that they are already signed up for the next semester.

Let’s continue here - The story ends ……

Start at the beginning – School days, school days ……….

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