AQA A2 Biology Unit 4

Gene
A selection of DNA that codes for the production of a particular polypeptide or protein.
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Locus
The position on a chromosome occupied by a particular gene.
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Allele
One of the different forms of a gene.
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Gene Pool
The total number of alleles in a particular population at a specific time.
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Allelic Frequency
The number of times an allele occurs within the gene pool.
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Dominant
Any allele that is always expressed in the phenotype of an organism; regardless if whether it is in the homozygous or heterozygous form.
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Recessive
Any allele that is only expressed in the phenotype of an organism if the dominant allele is not present.
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Co-Dominant
Any two alleles for one gene which are both expressed in the phenotype of an oragnism in a heterozygous organism.
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Genotype
The genetic composition of an organism. I.e. the allelic form; heterozygous, homozygous, recessive, dominant.
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Phenotype
The physical expression of the genotype of an organism.
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Sex-linked gene
A gene found only on the X chromosome and not on the Y chromosome.
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Multiple Alleles
A gene that has more than two possible alleles e.g. this is how blood groups are controlled.
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Poly-genes
A group of genes that are responsible for controlling one characteristic. Ratio of F2 generation is always 9:3:3:1
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Hardy-Weinberg Equations
To calculate allele frequency - p + q = 1 . To calculate phenotype frequency - p² + q² + 2pq = 1 with q = a and p = A
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Hardy-Weinberg Prediction
The proportion of dominant and recessive alleles of any gene in a population remains the same from on generation to the next provided that 5 conditions are met.
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Conditions for Hardy-Weinberg
Large population; Random mating; No migration (immigration/emigration) (i.e. no gene flow); No mutation; Natural selection.
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Directional Selection
Where selection may favour individuals that are at the extremes of the mean of the population. This changes the characteristics of the population and results in phenotypes at one extreme being selected for and the other extreme selected against.
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Stabilising Selection
Where selection may favour average individuals. This preserves the characteristics of a population.
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Geographical Isolation
Occurs when a physical barrier prevents two populations from breeding with one another. E.g. Oceans; Rivers; Mountain Ranges; Deserts. This can lead to the formation of a new species.
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Reproductive Isolation
Where two related species can't successfully interbreed producing fertile offspring due to genetic changes meaning they can't recognise each other. E.g. Differences in courtship behaviours and sexual organs meaning in incompatibility of the species.
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Respiration - Energy/ATP Production
Substrate-Level Phospohrylation - Occurs in Glycolysis and Krebs cycle. The direct linking of Pi and ADP to form ATP
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ATP (Adenosine Triphosphate)
Aka an Immediate energy source because ATP releases its energy very rapidly. The energy is released in a single step and is transferred directly to the reaction requiring it.
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Stages of Aerobic Respiration
(1) Glycolysis - Cytoplasm of cell (2) Link Reaction- Matrix of mitochondria (3) Krebs Cycle - Same as link reaction (4) Electron Transport Chain.
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Other cards in this set

Card 2

Front

The position on a chromosome occupied by a particular gene.

Back

Locus

Card 3

Front

One of the different forms of a gene.

Back

Preview of the back of card 3

Card 4

Front

The total number of alleles in a particular population at a specific time.

Back

Preview of the back of card 4

Card 5

Front

The number of times an allele occurs within the gene pool.

Back

Preview of the back of card 5
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