NCEA Level 2 Genetic variation

Allele

an alternative form of a gene

Centromere

point where the 2 chromatids are joined together.

Chiasma

the point at which chromatids break and re-join in crossing-over.

Chromosome

a structure in the nucleus made up of DNA which holds the genetic information of an organism

Homologous pair

a pair of chromosomes with the same genes but may have different alleles

Diploid

full or complete number of chromosomes 2n / 2 sets (= 46 in humans)

Dominant

an allele that is always expressed if present (only one copy needed)

Gamete

sex cell. Egg or sperm in humans

Gene

a section of a DNA molecule that codes for a protein/characteristic

Gene pool

the total variety of genes and alleles present in a sexually reproducing population available to be passed on to the next generation.

Genome

all of an organism's genes.

Haploid

half the normal number of chromosomes n / 1 set ( 23 in eggs or sperm)

Heterozygous

alleles are different eg. Tt

Homozygous

both alleles are the same eg. TT, tt

Linked

Genes that are located on the same chromosome

Locus

position of a gene on a chromosome

Meiosis

type of cell division producing four daughter cells each genetically different, with half the number of chromosomes of the parent cell (produces gametes)

Crossing-over

exchange of genetic material between homologous chromosomes (the inner chromatids) during meiosis

Independent assortment

Each homologous pair of chromosomes are lined up randomly and are sorted independently of the other pairs during meiosis putting chromosomes/alleles into new combinations increasing genetic variation

Segregation

In meiosis the two members of the pair of alleles of a gene becomes separated into different gametes (so the allele can join with a different allele of that gene at fertilisation)

Mutation

a sudden change in the genetic make up / in base order of DNA of an organism

Phenotype

how the gene is expressed/what the organism looks like. eg. tall.

Recessive

an allele that only expressed when it is present in two copies - the dominant allele must be absent

Somatic cells

body cells other than the sex cells.

Species

group of organisms which can interbreed sexually and produce fertile offspring.

Testcross

Finding the genotype of an individual showing dominant phenotypes by crossing them with a homozygous recessive individual and looking at the phenotypes of the offspring.

Adaptation

a feature an organism has which helps it survive in its environment. Can be structural, behavioural or physiological

Allele frequency

the proportion of a particular allele in a gene pool, relative to the other alleles of the same gene

Evolution

changes in the frequencies of alleles in a population over time

Natural selection

The process where individuals with favourable combination of traits are more likely to reproduce successfully and pass on these traits.

Gene flow

The introduction of genes/alleles from one population to the gene pool of another (Migration)

Gene pool

the total variety of alleles present in a sexually reproducing population available to be passed on to the next generation.

Genetic variation

All the genes, alleles and their combination present in a population

Genetic drift

random changes in allele frequencies in a population due to chance

Inbreeding

mating of closely related individuals of the same species

Population

members of the same species living in the same area at the same time

Environmental factors

factors which select for or against particular phenotypes (features) in the process of natural selection

Founders Effect

Change in allele frequencies when a new population arises from only a few colonising individuals. The new population will have reduced genetic diversity/smaller gene pool

Bottleneck Effect

Recovery of a population after a catastrophic event, the range of alleles will decrease and the frequencies of alleles will change. The recovered population will have reduced genetic diversity

Sexual Selection

Selection based on the choice of mating partners (usually female). This leads to evolutionary change if choices are based on differences in inherited characteristics (e.g. tail length in peacocks)

Selection Pressure

Abiotic or biotic factor that affects the

survival of an organism and therefore

influences reproductive success