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L2 Genetics
| Term | Definition |
|---|---|
| Characteristic | general expression of a gene, eg a form of the ripe seed, colour of the flower |
| Trait | alternative forms of the genetic characteristic, eg wrinkled seeds and smooth seeds, purple flowers and white flowers. |
| P1 generation | a cross made between two pure-breeding parent plants |
| F1 generation | first filial generation, the hybrid offspring of the P1 cross. |
| F2 generation | second filial generation, the offspring from inbreeding the F1 generation. |
| Genotype | The genetic make-up of an organism; the gene formula of an organism. |
| Phenotype | The physical, physiological, or chemical expression of an organism's genes, (ie what the trait looks like). |
| Allele | Alternative form of a gene at a locus. |
| Homozygous | Having two identical alleles for a given trait. |
| Heterozygous | Having two different alleles for a given trait. |
| Recessive allele | In a heterozygote, the allele that is completely masked in the phenotype. |
| Dominant allele | In a heterozygote, the allele that is fully expressed in the phenotype. |
| Hybrid | The offspring of two animals or plants of different races, breeds, varieties, species or genera. |
| Test cross or back cross | Breeding of an organism of unknown genotype with a homozygous recessive individual, to determine the unknown genotype. The ratio of phenotypes in the offspring determines the unknown genotype. |
| Incomplete dominance | A type of inheritance where the offspring shows a phenotype that is intermediate between the phenotypes of the parents eg red and white --> pink. |
| Lethal alleles | An allele that has a prominent visible effect as a heterozygote and is lethal as a homozygote. |
| Codominance | The phenotype of the offspring shows features of both parental traits. |
| Multiple alleles | Where there are more than two alternative alleles for a gene locus, eg blood groups |
| Monohybrid cross | A cross that considers parental varieties that differ in a single characteristic |
| Dihybrid cross | A cross that considers parental varieties that differ in two characteristics. |
| Sex-linked genes | Genes located on one sex chromosome but not the other (usually the X chromosome) eg haemophilia, colour-blindness. |
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kjsime