Introduction to genetics: Difference between revisions

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The information within a particular gene is not always exactly the same between one organism and another, so different copies of a gene do not always give exactly the same instructions. Each unique form of a single gene is called an [[allele]]. As an example, one allele for the gene for hair color could instruct the body to produce much pigment, producing black hair, while a different allele of the same gene might give garbled instructions that fail to produce any pigment, giving white hair. [[Mutation]]s are random changes in genes and can create new alleles. Mutations can also produce new traits, such as when mutations to an allele for black hair produce a new allele for white hair. This appearance of new traits is important in [[Introduction to evolution|evolution]].

# ==Genes and inheritance==

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# ==Genes and inheritance==

[[File:DNA animation.gif|frame|150px|left|A section of [[DNA]]; the sequence of the plate-like units ([[nucleotide]]s) in the center carries information.]]

Genes are pieces of DNA that contain information for the synthesis of ribonucleic acids (RNAs) or polypeptides. Genes are inherited as units, with two parents dividing out copies of their genes to their offspring. Humans have two copies of each of their genes, but each egg or sperm cell only gets ''one'' of those copies for each gene. An egg and sperm join to form a complete set of genes. The resulting offspring has the same number of genes as their parents, but for any gene'', one of their two copies comes from their father, and one from their mother.<ref name=Utah/>

The effects of this mixing depend on the types (the [[allele]]s) of the gene. If the father has two copies of an allele for red hair, and the mother has two copies for brown hair, all their children get the two alleles that give different instructions, one for red hair and one for brown. The hair color of these children depends on how these alleles work together. If one allele [[dominance (genetics)|dominates]] the instructions from another, it is called the ''dominant'' allele, and the allele that is overridden is called the ''recessive'' allele. In the case of a daughter with alleles for both red and brown hair, brown is dominant and she ends up with brown hair.<ref name=OMIM>[https://www.ncbi.nlm.nih.gov/omim/155555 Melanocortin 1 Receptor], Accessed 27 November 2010</ref>