inheritance Flashcards
gene
-a sequence of DNA bases that code for a polypeptide
allele
-a different version of the same gene
co-dominant
-every genotype has its own phenotype
phenotype
-the genetic makeup / alleles that can be influenced by the environment (the observable characteristics)
genotype
-what alleles the organism has (the genetic makeup)
genome
-the complete genes and genetic makeup of cells
proteome
-all of the possible proteins a cell can produce
dihybrid
-following 2 genes
linkage
-two genes that are on the same chromosome
epistasis
a form of gene interaction in which one gene masks the expression of the other (e.g. a widows peak being masked by baldness)
locus
-where the alleles are on the chromosome
meiosis
-DNA is replicated in interphase before meiosis occurs
-in the first division, there’s a separation of homologous chromosomes, which halves the chromosome number
-in the second division, there’s a operation of the sister chromatids
-this produces 4 genetically different daughter cells
homologous chromosome
-2 chromosomes in a pair, they’re the same length but different alleles
autosome
-one of the numbered chromosomes, that isn’t a sex chromosome
multiple alleles
-some characteristics are not inherited in such a simplistic way, some have multiple alleles e.g. blood group
blood groups
-AB, A, B, O
-determined by the antigens on the body cells
-A + B = co-dominant, O is recessive
hypostatic allele
-the allele that is being masked when epistasis occurs
why observed ratios might not be the same as expected ratios
-fertilisation is random, some of the outcomes are down to chance
-the sample size may be too small
mark-release-recapture
-collect the sample is a way that isn’t harmful
-mark the sample, in a way that isn’t harmful
-release and allow time to re-integrate
-collect a second sample and count the marks
(sample 1 x sample 2) / number marked in sample 2
hardy weinburg principle
p + q = 1
p^2 + 2pq + q^2 = 1
p= frequency of dominant allele in population
q= frequency of recessive allele in population
1= total population
how the hardy weinburg principle works
-large population
-mating is random
-no selection occurs
-no mutation occurs
-no immigration/ emigration occurs
stablising selection
-natural selection that keeps allele frequency constant over generations (e.g. human birth weights)
directional selection
-natural selection that produces a gradual change in allele frequencies over several generations (e.g. fish size in certain habitats)
-this usually happens when there’s a change in environment or a new favourable allele has been formed
disruptive selection
-natural selection that maintains a high frequency of two sets of alleles (e.g. different beaks for different size seeds)
-this can occur in an environment that shows variation
allopatric speciation
-occurs as a result of geographical isolation
-this could be a natural barrier (e.g. river) or a manmade barrier (e.g. a motorway)
-this creates 2 populations that are reproductively separated from on another and so no genetic exchange can occur
-this can lead to changes in phenotypes and alleles as the same species start to form separate species
-in future generations, they may begin to differ physiologically, behaviourally and structurally
sympatric seperation
-takes place with no geographical barrier, something happens and splits the two populations, that have no gene flow between them
-ecological separation is when they are separated because they live in different environments of the same area
-behavioural separation is when they separate due to behavioural differences (e.g. feeding)
genetic drift
-when populations are separated, they can go through natural selection or genetic drift
-genetic drift is when chance affects how individuals in a population survive/ breed (e.g. in a very small sample chance can affect which alleles are passed down, meaning favourable alleles may be lost)
-in large populations, genetic drift is less likely to occur
substation mutation
-this is when one nucleotide in the DNA sequence is replaced by another
-the effect of the change in an amino acid depends on the role of the original amino acids in the overall shape and function of the protein
-a substitution may not always be harmful as the substituted nucleotide may code in that triplet for the same amino acid
deletion mutation
-a deletion event is when a nucleotide in the DNA sequence is lost
-the loss of a single nucleotide can have a significant impact as it leads to a frame shift, resulting in completely different amino acids being coded for
