a section of a chromosome that controls a characteristic
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what is the definition of an allele
a different version of a gene (brown eye of eyes)
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what is dominant
only expressed in a heterozygous
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what is recessive
only expressed if homozygous
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what is genotype and phenotype
genotype = the combination of alleles one has phenotype = the physical characteristics someone has because of their genotype
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what is the difference between heterozygous and homozygous
heterozygous is having two different alleles and homozygous is both alleles the same
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describe the features of DNA
- long and thin - double helix
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what are the four nitrogenous bases
adenine, thymine, cytosine and guanine
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what is a chromosome
a very long DNA molecule (46 in one cell)
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what is DNA
molecules that contain different genes
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what cells are diploid which are haploid
all cells are diploid apart from sex cells
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what happens in mitosis
chromosomes get fatter/shorter membrane round nucleus beaks dow chromosomes replicate and join at centromere once attached to the spindle, it gets shorter pulling them apart the cell divides in two and forms membrane again
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differences between meiosis (1) and mitosis (2) ?
1: haploid cells, four cells per division, produce different cells 2: diploid cells, two cells per division, produce identical cells
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how is the sex determined?
definitely get an X from mother, so 50/50 whether get X or Y from father
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what are two genetically inherited diseases
cystic fibrosis and sickle-cell anaemia
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what processes involve mitosis
skin repair, immune system producing more lymphocytes, a-sexual reproduction
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