Genetics
From the Simple English Wikipedia, the free encyclopedia that anyone can change
Genetics is the study of how parents pass some of their characteristics to their children. It is an important part of biology, and gives the basic rules on which evolution acts.
The living things we see around us are made of millions of tiny self-contained components called cells. Inside of each cell are long molecules called DNA.[1] DNA stores information that tells the cells how to create that living thing. Parts of this information that tell how to make one small part or characteristic of the living thing - red hair, or blue eyes, or a tendency to be tall - are known as genes.
Every cell in the same living thing has the same DNA, but only some of it is used in each cell. For instance, genes that tell how to make parts of the liver are not used in the brain. What genes are used can also change over time. For instance, a lot of genes are used by a child early in pregnancy that aren't used later.
A living thing has two copies of each gene, one from its mother, and one from its father.[2] There can be multiple types of each gene, which give different instructions: one version might cause a person to have blue eyes, another might cause them to have brown. These different versions are known as "alleles" of the gene.
Since a living thing has two copies of each gene, it can have two different alleles of it at the same time. Often, one allele will be dominant, meaning that the living thing looks and acts as if it had only that one allele. The unexpressed allele is called recessive. In other cases, you end up with something in between the two possibilities. In that case, the two alleles are called "co-dominant".
Most of the characteristics that you can see in a living thing have multiple genes that influence them. But it's much easier to understand when there's just one gene, so we'll start with that.
[change] Mendellian Genetics
The basic rules of genetics were first discovered by a monk named Gregor Mendel in around 1865. But no-one paid much attention to his work until around 1900, when other scientists discovered genetics again.
[change] Punnett Squares
Developed by Reginald Punnett, Punnett squares are used by biologists to determine the probability of offspring to having a particular genotype.
| Maternal | |||
|---|---|---|---|
| B | b | ||
| Paternal | B | BB | Bb |
| b | Bb | bb | |
If B represents the allele for having black hair and b represents the allele for having white hair, the offspring of two Bb parents would have a 25% probability of having two white hair alleles (bb), 50% of having one of each (Bb), and 25% of having only black hair alleles (BB).
[change] Notes and References
- ↑ There are a few exceptions to this - red blood cells lose their DNA and most of their other structures before going into the blood, for instance.
- ↑ Again, mostly true: Some types of living things only have one parent.
