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Bio L2 Gen VarChange

NCEA Level 2 Biology Genetic Variation and Change AS 91157

TermDefinition
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.
alleles Different forms of a gene.
anaphase The stage of cell division in which chromosomes separate.
bottleneck effect A reduction in genetic diversity in a gene pool when a population is reduced to a few individuals.
centromere A narrow region of chromosomes where sister chromatids are joined and where spindle fibres attach prior to separation of the chromatids.
characteristic An inherited feature of an organism e.g. eye colour, coat colour.
chiasma (plural: chiasmata) A region of DNA exchanged between homologous chromosomes during crossing over.
chromatid Half of a replicated chromosome. It is identical to the other half, to which it is joined.
chromosome A single molecule of DNA bonded to various proteins.
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.
complete dominance When the dominant allele is always expressed in the phenotype, if present in the genotype. Only two phenotypes are possible – the dominant type and the recessive type.
continuous variation Variation in which individuals cannot be placed in distinct categories because there is a continuous range of intermediates between two extremes (e.g. body height).
crossing over The exchange of genetic material between homologous chromosomes during meiosis.
crossover value The percentage of offspring showing recombination. This gives a measure of the frequency of crossover events during meiosis, which indicates the distance between two linked genes.
dihybrid cross A genetic cross that considers two characteristics.
diploid Cells with two sets (i.e. homologous pairs) of chromosomes, one from each parent. Can be written as 2n.
discontinuous variation Variation in which individuals can be placed in categories which differ sharply from each other ('either-or' characteristics, e.g. blood groups).
DNA Deoxyribonucleic acid. The molecule that carries the genetic information within the chromosome.
DNA replication The process in which an identical copy of the DNA is made. It results in replicated chromosomes, each consisting of two identical sister chromatids.
dominant allele An allele that is expressed even in heterozygous individuals.
emigration Individuals moving out of a population. This can remove alleles from a population, decreasing genetic diversity.
enzyme A protein which catalyses biochemical reactions. It is specific to one type of reaction.
evolution Changes in the frequencies of alleles in the gene pool of a population.
F1 The first generation of offspring. Results from a cross between the parents.
F2 The second generation of offspring. Results from a cross between individuals in the F1 generation.
fitness The success of an individual’s phenotype in a particular environment. The greater this is, the more likely an individual is to survive and pass on its alleles to the next generation of offspring.
founder effect Random changes to a gene pool resulting from a few individuals establishing a new population.
gamete Sex cells (egg and sperm). Form during meiosis.
gametic mutation A mutation occurring in a sex cell (sperm or egg). This means it can be passed on to the next generation.
gene A section of DNA which codes for the production of a specific protein.
gene pool All the alleles that are present in a population.
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.
genome The total collection of genes possessed by an organism.
genotype The two alleles an individual has for a gene.
haploid The number of chromosomes found in a gamete (sex cell). Can be written as 1n.
heritable Able be passed on to future generations.
heterozygous When the two alleles an individual has for a trait are different.
homologous chromosomes A pair of similar-shaped chromosomes with the same genes in the same loci (positions). They may carry different forms of the gene e.g. A and a. One chromosome of each pair is inherited from each parent.
homozygous When the two alleles an organism has for a gene are the same.
immigration Individuals moving into a population. This can add new alleles to a population, increasing genetic diversity.
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).
locus (plural: loci) The specific location / position of a gene on a chromosome.
maternal From the female parent.
meiosis Cell division which results in the production of gametes, which are haploid.
metaphase The stage in cell division when chromosomes line up at the centre of the cell.
migration The movement of individuals, and therefore the transfer of their alleles, from one population to another.
monohybrid cross A genetic cross which considers just one characteristic.
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.
mutagen Any environmental factor which can cause a change in the DNA sequence (a mutation).
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.
offspring The next generation resulting from a genetic cross; the immediate descendants of the parents.
parental types When the combination of alleles is the same as a parent, e.g. when genes are linked.
paternal From the male parent.
phenotype The physical expression of the genotype.
population A group of individuals of the same species living in the same area.
pure-breeding When an individual is homozygous for a trait. This means there is only one type of allele it can pass to its offspring.
recessive allele The form of a gene which is only expressed only if an individual has two of them.
recombinant When the combination of alleles is different to either of the parents. This is caused by crossing over between alleles which were linked.
recombination The exchange of genetic material between adjacent chromatids of homologous chromosomes during meiosis. This results in new combinations of alleles on the chromosomes.
replicated chromosome A chromosome made up of two identical sister chromatids, formed during DNA replication.
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.
sister chromatids The two identical halves which make up a replicated chromosome. Sister chromatids form during DNA replication and separated during anaphase of cell division.
somatic mutation A mutation occurring in any cell of the body other than the gametes. It cannot be passed on to the next generation.
test cross When an individual of unknown genotype is bred with a homozygous recessive individual. The ratio of phenotypes in the offspring may reveal the unknown genotype.
trait Alternative forms of the genetic characteristic, e.g. blue eyes, brown eyes.
variation Differences between individuals. This can be in terms of alleles (genetic variation) or phenotypes.
zygote A fertilised egg.
somatic cell Any cell of an organism other than a gamete.
Created by: nztcowen