- Cells in your body have a nucleus.
- Chromosomes are found in the nucleus
- Each chromosome is one very long bit of DNA.
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- 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
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- 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.
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- 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.
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