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L2 Gen Var TOP 20
NCEA Level 2 Biology Genetic Variation and Change
Term | Definition |
---|---|
allele frequency | The proportion of that form of the gene in the gene pool. Calculated as: number of that allele ÷ total number of all alleles for that gene in the gene pool. |
bottleneck effect | A reduction in genetic diversity when a population is reduced to a small number individuals. It is chance which survive. |
codominance | The genetic pattern in which both alleles are separately expressed in the phenotype of heterozygous individuals (e.g. two different colours). |
crossing over | The exchange of genetic material between homologous chromosomes during meiosis. |
founder effect | Random changes to a gene pool resulting from a few individuals establishing a new population. |
gametic mutation | A mutation occurring in a sex cell (sperm or egg). This means it can be passed on to the next generation. |
genetic variation | The range of all the alleles in a population; the greater the number of different alleles present, the greater this is. |
genetic drift | The change in allele frequencies in populations due to chance events (not selection). It may include the loss of alleles from a gene pool. The effects are greatest in small populations. |
incomplete dominance | The genetic pattern in which the phenotype of heterozygous individuals is intermediate between the homozygous phenotypes (e.g. pink vs red & white). |
independent assortment | The order in which a chromosome pair lines up during meiosis is not affected by the order in which any other pair lines up. Each pair is ‘sorted’ separately into gametes. |
lethal alleles | This is when a mutation results in a non-functional version of an essential protein. The individual may not survive to be born. |
linked genes | When the alleles for two different genes are located on the same chromosome. This means they are inherited together (unless they are separated by crossing over). |
meiosis | Cell division which results in the production of gametes, which are haploid. |
migration | The movement of individuals, and therefore the transfer of their alleles, from one population to another. |
multiple alleles | These are genes for which more than two different alleles exist. e.g. human blood groups, in which there is an A, B and O allele. |
mutation | A sudden, permanent change in the DNA sequence of an individual. This is the only source of new alleles. |
natural selection | Individuals in a population which are best suited to the conditions leave the most offspring. This changes the allele frequencies in the gene pool. |
segregation | The separation, during meiosis, of the two alleles which an individual has for a gene. |
somatic mutation | A mutation occurring in any cell of the body other than the gametes. It cannot be passed on to the next generation. |