B1 Revision - You and Your Genes (OCR 21st Century)

Mind Map by marauder, updated more than 1 year ago
Created by marauder about 5 years ago


Mind Map on B1 Revision - You and Your Genes (OCR 21st Century), created by marauder on 11/30/2014.

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B1 Revision - You and Your Genes (OCR 21st Century)
1 Most cells in your body have a nucleus
1.1 This contains your genetic material
1.1.1 Your genetic material is arranged into chromosomes. There are 23 pairs of chromosomes in the human cell nucleus. Each chromosome is one very long molecule of DNA. A gene is a short length of a chromosome. Genes control the development of different characteristics - for example, hair colour Genes can exist in different versions. Each version gives a different form of a characteristic, like blue or brown eyes. The different versions of the same gene are called alleles. Genes are instructions for making different proteins. Proteins are the building blocks of cells. Having different versions of proteins means we end up with different characteristics. Structural proteins: part of things like skin, blood, hair, and the cytoplasm in cells. Collagen is a structural protein that is found in tendons, bones and cartilage. Functional proteins: Enzymes are proteins that help with digestion by breaking down food molecules - amylase is a digestive enzyme that breaks down starch to maltose.
2 An organism's genotype describes the genes it's got.
2.1 An organism's genotype is all the genes it has.
2.2 The characteristics an organism displays are it's phenotype.
2.3 Some characteristics are controlled only by genes.
2.3.1 This can only be one gene, or quite often, the characteristic is controlled by several genes working together: eg, eye colour.
2.4 However some characteristics are controlled only by environmental factors such as scars. They have nothing to do with genes.
2.5 Some characteristics are controlled by genes and the environment, for example, weight
3 Genes and variation
3.1 In body cells (all your cells apart from sex cells), chromosomes come in pairs.
3.1.1 One chromosome in every pair has come from each parent. The sex cells (sperm and egg) are different from ordinary body cells because they contain just 23 single chromosomes - one from each pair. When the sperm fertilises the egg, the 23 chromosomes from the egg combine with the 23 from the sperm. The fertilised egg now has 23 pairs of chromosomes, just like an ordinary body cell. The two chromosomes in a pair always carry the same genes. 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.
3.2 Children resemble both parents, but are identical to neither.
3.2.1 Half a child's chromosomes come from each parent. That means children get some alleles from each of their parents, which is why some children look like a bit of both of their parents. Every child has a unique combination of alleles, which is why no two people in the world are the same - apart from identical twins.
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