Genes, Chromosomes and DNA: alleles, genotype and proteins

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Biology

Genes, Chromosomes and DNA

1.) Most cells in your body have a nucleus- and its the nucleus that contains your genetic material.

2.) The genetic material in the nucleus is arranged into chromosomes. The human cell nucleus contains 23 pairs of chromosomes.

3.) Each chromosome is one very long molecule of DNA that's coiled up.

4.) A gene is a short length of a chromosome.

5.)Genes control the development of different characteristics, e.g hair colour, and how and organism functions

6.) Genes can exist in different versions. Each version gives a different form of characteristic, like blue or brown eyes. The different version of the same gene are called alleles.

Genes are instructions for cells

Each gene is a code for making a certain protein. Proteins are the building blocks of cells. Having different versions of proteins means that we end up with different characteristics

1.) Some proteins are structural proteins . They're part of things like, skin, hair, blood and the cytoplasm in our cells. E.g collagen is a structural protein that is found in tendons, bones and cartillage

2.)Other proteins are functional proteins. For example, enzymes are proteins that help with digestion by breaking down food molecules - amylase is a digestive enzyme that breaks down starch to maltose

An organisms geneotype describes the genes its got

1.)An organisms geneotype is all of the genes it has. The characteristics that an organism displays are called its phenotype.

2.) Some characteristis, e.g dimples are controlled only by genes. This can just be one gene, or quite often the characteristics is controlled only by several genes working together, e.g eye colour.

3.) Other characteristics, e.g scars are controlled only by environmental factors. They don't have anything to do with genes and are caused by things like how and where you live.

4.)These are also characteristics that are controlled by both genes and environmental factors. For example weight - if both your parents are skinny, you'll probably be skinny.

Sperm and egg cells have half the normal amount of DNA

1.) The sex cells are different from ordinary body cells because they contain just 23 single chromosomes - that's one chromosome from each pair

2.) When the sperm fertilises

the egg, the 23 chromosomes in the sperm combine with the 23 chromosomes in the egg.

3.) The fertilised egg then has 23 pairs of chromosomes, just like an ordinary body cell.

4.)The two chromosomes in a pair always carry the same genes and each gene is always found in the same place on the two chromosomes. Because the two chromosomes in a pair came from different parents, they might have different alleles of these genes. Alleles are different versions of the same gene.

Children resemble both parents, but are identical to neither

1.) Children get some of their alleles from each of their parents.

2.)This is why most children look a bit like both of their parents

3.)But they wont be exactly like either one of their parents because they haven't got all the same alleles - some came from the other parent

4.) In fact, every child will have a new, unique combination of alleles- that's why no two people in the world are exactly the same

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