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GCSE Biology > Genetic Terminology

DNA The molecule which contains genes. It's shaped like a double helix (a spiral)
Chromosomes Found in the cell nucleus: X-shaped things made up of long coils of DNA
Chromatids The separate arms of the chromosomes
Centromere Area at centre of chromosome where the separate arms meet
Gene Section of DNA molecule
Allele A gene, but there are two types of alleles
Homozygous An organism with two alleles the same for a particular gene (e.g. HH or hh)
Heterozygous An organism with two alleles that are different (e.g. Hh)
Dominant An allele/gene that determines the characteristics in the organism (dominant over the recessive allele)
Recessive Does not usually affect the phenotype of the organism
Genotype The description of the GENES you have (e.g. MM or Hh etc...)
Phenotype The description of your PHYSICAL ATTRIBUTES (e.g. hair colour)
Mitosis Cell division - one cell splits into two identical cells
Meiosis Cell division - produces haploid cells (the sperm / egg cells)
Diploid Describes a cell with the full number of chromosomes (46 for humans)
Haploid Describes a cell with half the full number of chromosomes
Zygote A newly formed life just after fertilisation of the egg by the sperm
Gamete A sperm / egg cell (both haploid)

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