Ask a Geneticist

We have 46 different chromosomes instead of one big long chain of genes because of many reasons. The first one is because it is easier to reproduce that way. Simple organisms like bacteria only have one chromosome. They only reproduce by duplicated themselves, so variety doesn't matter. With humans and other complex organisms, we reproduce sexually meaning we get chromosomes from both parents. With different chromosomes, more different groupings are possible (10 trillion) and the process is completely random. Genetic diversity is important since we have to be different to survive. If a disease started to cause havoc, many would die. The ones who live would have different genes, and that is what will help us to continue the human race.

Our genes are in certain chromosomes for no specific reason. Over time (generations), genes move around and group themselves in different chromosomes. Genes that are associated with each other can be separated by a few chromosomes. However, some parts are organised. A process called gene duplication helps genes become more organised. Basically, duplicated genes develop new jobs over time, and genes close to each other generally do similar jobs. Scientists still aren't completely sure about the final answer to many of our questions about genetics (and other mysteries of our world), but discoveries are being made by the minute, and it's only a matter of time.

Tour of the Basics - Genetics

Two things learned from the site:

1. All humans have two sets of chromosomes (the sets have 23, so 46 in all). When two humans get a child, they each give one set to the baby. Therefore, the genes are a mix of both parents. A sperm and egg cells have only one set of chromosomes, unlike our other cells. When these two cells join, they form one cell with two sets of chromosomes. The chromosomes that the baby can receive can be from any of the four sets, but it must have one of each and only 46. The sets are given randomly, so every baby is different.

2. Traits can be physical (how they look), behavioral (how they act), or even a medical condition passed down. Our traits are shaped by our genes and environment. Alleles are what scientists use to describe genetic information. Traits are determined by what alleles you have. Homozygous is when someone has two of the same allele (purebred). Sometimes, people will have two different alleles. Then, the dominant allele will overpower the recessive one. For example, brown eyes are a dominant allele while blue eyes are recessive. If someone had both alleles, they would have brown eyes. Heterozygous is what this type of situation (two different alleles) is called. A child will get one allele from each parent, making different combinations possible. This isn't the case for all types of inheritance. Sometimes, the dominance level will be equal and the result will be a combined version. Traits influenced by one gene is rare, and they are called single-gene traits. Complex-gene traits, traits from more than one gene, are more common.