Genetics OCR Biology A2
- Created by: Erin
- Created on: 03-05-15 21:35
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- Genetics
- Genotype
- Genetic makeup of an organism
- Determined by genotype and environment
- e.g. Humans intelligence is partly determined by genes and partly environment - got genetic potential? must be placed in stimulating learning environment
- Phenotype
- Physical appearance of a genotype
- Determined by genotype and environment
- e.g. Humans intelligence is partly determined by genes and partly environment - got genetic potential? must be placed in stimulating learning environment
- Codominant
- Characteristic where both alleles contribute to the phenotype
- Linkage
- refers to 2 or more genes that are located on the same chromosome
- Reduces the number of phenotypes resulting from a crossover
- If genes re linked, during crossing over, there is a LOWER CHANCE of chiasmata forming between the 2 loci, because they are v close together. So usually, the specific combinations of alleles present on each of the parental chromosomes, remain unchanged by crossing over.
- The linked alleles are more than likely than expected to be inherited together
- So there will be fewer different genotypes than expected resulting from this cross so a different ratio of phenotypes produced. The linked genes begin to behave as if they are 1 gene
- Reduces the number of phenotypes resulting from a crossover
- If genes re linked, during crossing over, there is a LOWER CHANCE of chiasmata forming between the 2 loci, because they are v close together. So usually, the specific combinations of alleles present on each of the parental chromosomes, remain unchanged by crossing over.
- The linked alleles are more than likely than expected to be inherited together
- So there will be fewer different genotypes than expected resulting from this cross so a different ratio of phenotypes produced. The linked genes begin to behave as if they are 1 gene
- So there will be fewer different genotypes than expected resulting from this cross so a different ratio of phenotypes produced. The linked genes begin to behave as if they are 1 gene
- The linked alleles are more than likely than expected to be inherited together
- If genes re linked, during crossing over, there is a LOWER CHANCE of chiasmata forming between the 2 loci, because they are v close together. So usually, the specific combinations of alleles present on each of the parental chromosomes, remain unchanged by crossing over.
- Reduces the number of phenotypes resulting from a crossover
- So there will be fewer different genotypes than expected resulting from this cross so a different ratio of phenotypes produced. The linked genes begin to behave as if they are 1 gene
- The linked alleles are more than likely than expected to be inherited together
- If genes re linked, during crossing over, there is a LOWER CHANCE of chiasmata forming between the 2 loci, because they are v close together. So usually, the specific combinations of alleles present on each of the parental chromosomes, remain unchanged by crossing over.
- Epistasis
- The interaction of different gene loci so that 1 gene locus masks or suppresses the expression of another gene locus
- The homozygous presence of a recessive allele (1) may prevent the expression of another allele (2) at a second locus
- The alleles at the first locus (1) are EPISTATIC to the alleles at the second locus (2), which are hypostatic
- is not INHERITED, it is an interaction between the 2 gene loci - it reduces phenotypic variation
- Recessive epistasis
- F2 Generation 9:3:4
- 9 - both dominant
- 3 - dominant, epistatic, other recessive
- 4 - recessive epistatic
- Cross homozygous recessive parent with a homozygous dominant parent
- F2 Generation 9:3:4
- 9 - both dominant
- 3 - dominant, epistatic, other recessive
- 4 - recessive epistatic
- F2 Generation 9:3:4
- F2 Generation 9:3:4
- Dominant epistasis
- 13:3
- 12:3:1
- crossing a homologous recessive parent with a homologous dominant parent
- 12 - dominant epistatic
- 3 - recessive epistatic dominant
- 1 - both recessive
- 'Complementary fashion'
- 1) Cross 2 strains of white-flowered sweet peas - all F1 generation have purple flowers
- 2) Interbreed F1 generation. F2 generation 9:7
- Untitled
- 2) Interbreed F1 generation. F2 generation 9:7
- 1) Cross 2 strains of white-flowered sweet peas - all F1 generation have purple flowers
- Chi-squared test
- statistical test to find out the difference between observed categorical data and expected data is small enough to be due to chance
- Conditions
- 1) relatively large sample size 2) Only raw counts 3) there are no zero scores
- Variation
- Intraspecific variation - within a speceis
- Interspecific variation = between different species
- Discontinuous Variation - qualitative differences between phenotypes. No intermediate categories
- Continuous Variation - quantitative differnces between phenotypes - wide variations within a population no distint categories
- Genotype
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