Genes, chromosomes and DNA 0.0 / 5 ? Applied ScienceChromosonesBTEC NationalEdexcel Created by: Jessie SbresniCreated on: 16-02-15 11:41 Chromosomes Cells in your body have a nucleus. Chromosomes are found in the nucleus Each chromosome is one very long bit of DNA. 1 of 4 DNA DNA is double helix Each of the two DNA strands contain 'bases' DNA has four different bases A= Adelnine C= Cytosine G= Guanine T= Thymine A always pairs up with T C always pairs up with G Called complementary base-pairing 2 of 4 Alleles In a nucleus of each cell, there are two copies of every chromosome. This means that each cell has two copies of every gene. For example, you've got two copies of the gene that control your eye colour. You can have different versions of the same gene. These are called alleles. Two different alleles are called heterozygous. Two alleles the same are called homozygous. 3 of 4 Controlling characteristics We use letters to show the alleles that an organism has. You have two alleles for each gene. Each one can be either dominant or recessive. Big letters= dominant alleles Small letters= recessive alleles. Genotype means what alleles you have, Bb Phenotype means the actual characteristic 'brown eyes'. If both alleles are dominant, you have a dominant characteristic If both alleles are recessive, you have a recessive characteristic. If you have one dominant and one recessive allele, you will only have the dominant characteristic. 4 of 4
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