MODULE 6 Flashcards
transcription factors
proteins that bind to DNA and switch genes on and off by increasing or decreasing the rate of transcription
body plan
is the general structure of an organism arranged in a particular way
apoptosis
when some cells die and break down as a normal part of development
continuous variation
where the individuals in a population vary within the range and there are no distinct categories
discontinuous variation
when there are two or more distinct categories so no intermediates
gene
a sequence of bases on a DNA molecule that codes for a protein which results in a characteristic
allele
a different version of a gene
genotype
the alleles an organism has
phenotype
the characteristics the alleles produce
dominant
an allele whose characteristic appears in the phenotype even when there is only one copy
recessive
an allele whose characteristic only appears in the phenotype if 2 copies are present
codominant
alleles that are expressed in the phenotype, neither one is recessive
locus
the fixed position of a gene on a chromosome
homozygote
an organism that carries 2 copies of the same allele
heterozygote
an organism that carries 2 different alleles
carrier
a person carrying an allele which is not expressed in the phenotype but that can be passed on to the offspring
epistasis
when the allele of one gene masks the expression of the alleles of other genes
evolution
the change in allele frequency
allele frequency
how often an allele occurs in a population
stabilising selection
individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce
directional selection
individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce
genetic drift
chance dictates which alleles are passed on
genetic bottleneck
an event that causes a big reduction in a populations size, leading to a reduction in the gene pool
artificial selection
when humans select individuals in a population to breed together to get desirable results
speciation
development of new species
species
a group of similar organism that can reproduce to give fertile offspring