Genetics - What are Genes?
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Genetics - What are Genes?
Inside every cell of each living thing (plant or animal) are sets of instructions called genes. The genes provide the instructions on what is the plant or animal, what it looks like, how it is to survive, and how it will interact with its surrounding environment. The genes are strung together in long stands of material called deoxyribonucleic acid (DNA) and these long strands are called chromosomes. Most living things have pairs of chromosomes (one from each parent), though they may have a different number of chromosomes from another living thing. For example, humans have 23 pairs of chromosomes and the fruit fly has 4 pairs.
Each gene is made up of long combinations of four different nucleotide bases. It is the various combinations of the nucleotide bases that determine everything about a living creature.
The four nucleotides are called:
The gene for green eyes might have this nucleotide sequence.
The gene for blue eyes might have this nucleotide sequence.
Notice how the nucleotide sequences below are very similar. The only difference being the last two bases. They both describe an eye with the last two characters stating the color of the eye.
Note: These gene formula are not accurate, the correct sequence could be up to several thousand bases long).
Many of the genes have a quality known as Dominate or Recessive. Dominant traits are more common than Recessive traits due to this quality.
Why do I have blue eyes when both my mother and father have brown eyes?
Each person has two genes for eye color. When a person has two identical genes, he will have eyes of that color. Another person may two different genes, and she will have eyes the color of the dominant gene. With eye color, the gene for brown eyes is dominant (B). The gene for Blue eyes is recessive (b). If a person has one B gene and one b gene or two B genes, then that person will have brown eyes. If a person has bb eye genes, then the person will have blue eyes.
Parents with Brown Eyes and Recessive Genes
In this diagram, both the mother and father have brown eyes, but they both have the recessive gene for blue eyes as part of their genetic makeup. There is a 1 in 4 or 25% chance that their child will have blue eyes.
One Brown Eyed Parent with Recessive Gene
In this diagram, the mother has brown eyes with the recessive blue eye gene and the father has blue eyes. There is a 1 in 2 or 50% chance that their child will have blue eyes.
Brown Eyed Parent without Recessive Gene
In this diagram, the father has blue eyes and the mother has brown eyes without the recessive gene. In all of the possible combinations for the children, there is one of the dominant B genes. All of the children will have brown eyes.
The results would be the same in diagram 2 if the Mother had blue eyes and the Father had Brown eyes with a recessive blue gene, or in diagram 3 if the Father had the brown eyes and the Mother had blue eyes.
1. Why is DNA described as the “double helix of life”?
2. Where are chromosomes found within a living cell?
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