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L2 Gen Var TOP 20

NCEA Level 2 Biology Genetic Variation and Change

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 in a gene pool when a population is reduced to a few individuals.
codominance When both alleles are present, i.e. in a heterozygous individual, both are expressed in the phenotype. Both alleles are equally and independently expressed.
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 When both alleles are present, i.e. in a heterozygous individual, this results in a phenotype which is intermediate between the homozygous types.
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 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 Alleles which are on different chromosomes will separate independently. For example, if parent is AaBb, any one gamete could be AB, Ab, aB or ab. There is an equal chance of each combination.
somatic mutation A mutation occurring in any cell of the body other than the gametes. It cannot be passed on to the next generation.
Created by: nztcowen