Biology AS Edexcel Snab Revision
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lifestyle-health-and-risk as19 主题
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diet-and-health interpreting-data-on-risk-factors
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diet-and-health treatment-of-cvd
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diet-and-health energy-budgets-and-diet
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diet-and-health monosaccharides
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diet-and-health the-glycosidic-bond
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diet-and-health disaccharides
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diet-and-health polysaccharides
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diet-and-health lipids-and-ester-bonds
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diet-and-health reducing-risk-factors-of-cvd
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diet-and-health practical-vitamin-c-content
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the-circulatory-system the-need-for-a-circulatory-system
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the-circulatory-system the-importance-of-water-in-transport
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the-circulatory-system mammalian-heart-structure-and-function
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the-circulatory-system blood-vessels-structure-and-function
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the-circulatory-system cardiac-cycle
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the-circulatory-system investigating-heart-rate
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the-circulatory-system atherosclerosis
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the-circulatory-system blood-clotting
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diet-and-health cardiovascular-disease
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diet-and-health interpreting-data-on-risk-factors
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genes-and-health as28 主题
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gas-exchange-cell-membranes-and-transport properties-of-gas-exchange-surfaces
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gas-exchange-cell-membranes-and-transport ficks-law-of-diffusion
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gas-exchange-cell-membranes-and-transport the-mammalian-lung
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gas-exchange-cell-membranes-and-transport cell-membranes
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gas-exchange-cell-membranes-and-transport practical-investigating-membrane-permeability
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gas-exchange-cell-membranes-and-transport diffusion-and-facilitated-diffusion
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gas-exchange-cell-membranes-and-transport active-transport
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gas-exchange-cell-membranes-and-transport osmosis
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nucleic-acids nucleotides-and-phosphodiester-bonds
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nucleic-acids dna-structure
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nucleic-acids rna-structure
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proteins transcription
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proteins translation
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proteins nature-of-the-genetic-code
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proteins amino-acids-and-peptide-bonds
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proteins levels-of-protein-structure
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proteins globular-proteins-structure-and-function
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proteins fibrous-proteins-structure-and-function
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proteins the-role-of-enzymes
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proteins mode-of-enzyme-action
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proteins enzyme-and-substrate-concentrations
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inheritance dna-replication
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inheritance mutations
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inheritance inheritance-key-terms
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inheritance pedigree-diagrams
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inheritance monohybrid-crosses
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inheritance chi-squared-test
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inheritance genetic-screening
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gas-exchange-cell-membranes-and-transport properties-of-gas-exchange-surfaces
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voice-of-the-genome as19 主题
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cell-structure-and-organisation cell-theory
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cell-structure-and-organisation eukaryotic-cells
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cell-structure-and-organisation prokaryotic-cells
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cell-structure-and-organisation organisation-of-cells
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cell-structure-and-organisation microscopy
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cell-structure-and-organisation magnification-calculations
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cell-structure-and-organisation recognising-organelles
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cell-division the-cell-cycle
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cell-division mitosis
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cell-division practical-identifying-mitosis-in-plant-cells
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reproduction-and-inheritance mammalian-gametes
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reproduction-and-inheritance fertilisation-in-mammals
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reproduction-and-inheritance genes-and-linkage
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reproduction-and-inheritance meiosis-source-of-genetic-variation
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differentiation-and-variation stem-cells
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differentiation-and-variation stem-cells-in-medicine
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differentiation-and-variation cell-differentiation
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differentiation-and-variation epigenetics
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differentiation-and-variation phenotypes-and-variation
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cell-structure-and-organisation cell-theory
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biodiversity-and-natural-resources as19 主题
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biodiversity the-variety-of-life
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biodiversity measuring-biodiversity-within-a-habitat
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biodiversity comparing-biodiversity-between-habitats
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biodiversity ecological-niches-and-adaptations
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biodiversity natural-selection
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biodiversity hardy-weinberg-equation
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biodiversity reproductive-isolation
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biodiversity classification
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biodiversity conservation-of-biodiversity
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resources-from-plants plant-cell-structure
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resources-from-plants plant-stems
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resources-from-plants importance-of-water-and-inorganic-ions-to-plants
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resources-from-plants starch-and-cellulose-structure-and-function
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resources-from-plants plant-fibres
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resources-from-plants practical-identifying-tissue-types-within-stems
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resources-from-plants tensile-strength-plant-fibres
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resources-from-plants development-of-drug-testing
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resources-from-plants antimicrobial-properties-of-plants
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resources-from-plants sustainability-and-plant-materials
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biodiversity the-variety-of-life
inheritance monohybrid-crosses
Exam code:8BN0
Monohybrid Crosses
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Monohybrid inheritance looks at how the alleles for a single gene are passed on from one generation to the next
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Known information about the genotypes, phenotypes and the process of meiosis are used to make predictions about the phenotypes of offspring that would result from specific breeding pairs
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When two individuals sexually reproduce there is an equal chance of either allele from their homologous pair making it into their gametes and subsequently the nucleus of the zygote
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This means there is an equal chance of the zygote inheriting either allele from their parent
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Genetic diagrams are often used to present this information in a clear and precise manner so that predictions can be made
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These diagrams include a characteristic table called a Punnett square
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The predicted genotypes that genetic diagrams produce are all based on chance
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There is no way to predict which gametes will fuse so sometimes the observed or real-life results can differ from the predictions
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Genetic crosses can be shown by a Punnet square
Worked Example
Worked example: Genetic diagram
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One of the genes for the coat colour of horses has the following two alleles:
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B, a dominant allele produces a black coat when present
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b, a recessive allele produces a chestnut coat when present in a homozygous individual
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In this example a heterozygous male is crossed with heterozygous female
Parental phenotype: Black coat x Black coat
Parental genotypes: Bb x Bb
Parental gametes: B or b x B or b
Monohybrid Punnett square with Heterozygotes Table
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Predicted ratio of phenotypes in offspring – 3 black coat : 1 chestnut coat
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Predicted ratio of genotypes in offspring – 1 BB : 2 Bb : 1 bb
Examiner Tips and Tricks
You need to be able to interpret genetic diagrams so take some time to get familiar with different sorts of diagrams such as pedigree charts and Punnet squares.
Responses