2.5 Genetic variation and change Flashcards
multiple alleles
a gene that has more than two alleles
linked genes
genes found on the same chromosome. linkage increases the closer they are are and ones close together are more likely to be in the same gamete
homozygous
an organism which has two alleles that are the same (BB)
heterozygous
an organism which has two alleles that are different (Bb)
genotype
the genetic makeup of an organism
phenotype
the physical expression of a gene
allele
a variant of a gene which is inherited
lethal alleles
alleles that produce a phenotypic effect causing the death of an organism. it is caused by the mutation of an essential gene - causing an essential protein to no longer be produced functionally. if heterozygous, the organism will be a carrier (and most likely survive)
incomplete dominance
alleles which are mixed in expression ex. blue + yellow = green
co-dominance
when two alleles are identically dominant and are thus expressed equally
ex. blue + yellow = blue + yellow
monohybrid cross
a cross (punnet square) that involves only one gene
ex. eye colour
dihybrid cross
a cross (punnet square) that involves two different genes being inherited
ex. eye and hair colour
fillal
relating to an organisms child (the equivalent of “paternal” but for offspring)
pedigree chart
family trees showing the presence/absence of a trait
test cross
breeding an organism with an unknown genotype with one that is homozygous recessive
mutation
a permanent change to the DNA base sequence, it is the only way new alleles are made
mutagens
environmental factors, such as UV light, which increases the likelihood of mutations
neutral mutation
a mutation with neither positive or negative impacts
silent mutation
no observable impact, usually because amino acid has not changed
block mutation
changes to a segment of chromosome (could be several genes)
includes inversion, deletion, duplication and translocation
inversion mutation
where sections of DNA swap places
deletion mutation
where a section of DNA is removed
duplication mutation
where a section of DNA is repeated
translocation mutation
where a section of DNA is added from another chromosome
stop codon
a specific sequence which tells the ribosomes to stop making proteins. mutations can cause a stop codon to be made prematurely, leading the rest of the DNA “code” to be lost OR prolong the stop codon
point mutation
a small number of base pair changes
homologous chromosomes
two chromosomes that share the same structural features, such as size, banding pattern and centromere position. they also have the same genes at a specific loci position. one chromosome in each pair is from a parent
DNA
DNA is a polymer made of “deoxyribose” a nucleotide monomer. in eukaryotes, the DNA supercoils around a histone protein
non-favourable alleles
alleles that will be lost from the population because individuals possessing them will have reduced reproduction and survival
genetic drift
the change in allele frequency in a population due to chance events
genetic biodiversity
the range of all the alleles present in the gene pool. important to the survival of a species because the greater the range of alleles, the greater the variation within the population
favourable alleles
will be passed on to offspring
selection pressure
a biotic or abiotic factor which effects the survival of an organism and therefore influences reproductive success in a population. some members of the population will not survive and reproduce and thus will not pass on their genes into the next generation
template strand
the sequence of DNA that is used during the synthesis of mRNA
coding strand
the opposite strand directly corresponding to the mRNA sequence
tRNA
brings in the amino acids
