Biology 2.3 Genetics (NZ NCEA LEVEL TWO)

any chromosome that is not a sex chromosome
Back Cross
The individual with the unknown genotype is bred with a homozygous recessive individual. (test cross)
Continuous Variation
Variation measured on a continuum rather than in discrete units or categories (eg height in human beings).
Crossing Over
the interchange of sections between pairing homologous chromosomes during the prophase of meiosis
Dihybrid inheritance
Considers 2 different alleles from each parent
discontinuous variation
characteristics that have either one phenotype or another eg. tongue rolling, eye colour etc.
Dominant Allele
an allele whose trait always shows up in the organism when the allele is present
gametic mutation
A mutation in the sex cells. Can be inherited.
genetic makeup of an organism
independant assortment
the process of random segregation and assortment of chromosomes
law of segregation
members of a pair of homologous chromosomes separate during the formation of gametes and are distributed to different gametes so that every gamete receives only one member of the pair
cell divison that produces gametes
monohybrid inheritance
inheritance of a single trait, controlled by alleles of a single gene
any agent (physical or environmental) that can induce a genetic mutation or can increase the rate of mutation. (mutagens are, ionising radiation, viruses & microbes, environmental poisons, alcolol and diet.)
a permanent change in the genetic code.
The physical expression of a gene
recessive allele
an allele that is masked when a dominant allele is present
The alternate form of a gene
the exchange of alleles between homologous chromosomes.
sex chromosome
chromosomes that code for gender (XX =female XY=male)
somatic mutation
mutation in body cells. These can not be inherited
test cross
The individual with the unknown genotyoe is bred with a homozygous recessive individual. (back cross)
any difference between individuals of the same species
Gene mutations
Mutations that produce changes in a single gene
Chromosome Mutations
Either changes in structure of a chromosome or the loss of an entire chromosome
mate selection
Individuals select for desired phenotypes in mates. (prefereble traits will become more common in the gene pool)
Significance of meiosis
ensures that offspring have the correct amount of chromosomes in the somatic cells
Stages of Meiosis
interphase, prophase1, metaphase1, anaphase1, telophase1, prophase2, metaphase2, anaphase2, telophase2,
term used to refer to an organism that has two different alleles for the same trait eg Bb
term used to refer to an organism that has the same alleles for one trait, having two identical alleles for a trait eg BB, bb
a genetically determind characterisitc.
the change in an organism over time
inherited characteristic that increases an organism's chance of survival
allele frequency
how often a form of a gene appears in a gene pool
artificial selection
selection by humans for breeding of useful traits from the natural variation among different organisms
founder effect
change in allele frequencies as a result of the migration of a small subgroup of a population forming a new population
natural selection
a natural process resulting in the evolution of organisms best adapted to the environment
genetic drift
The gradual changes in gene frequencies in a population due to random events
gene flow
exchange of genes between populations
movement of individuals (and therefore alleles) into a population
movement of individuals (and therefore alleles) out of a population
bottleneck effect
Genetic drift resulting from a drastic reduction in population size
Stabilising selection
extremes variations are selected against.
directional selection
one extreme is selected for
disruptive selection
extreme phenotypes are selected for over the intermediate forms.