6.1.2 - patterns of inheritance Flashcards
phenotypic variation
the variation between observable characteristics of an organism
example of variation through a combination of genetic and environmental factors
- plants have green leaves because their genes code for chlorophyll, however chlorosis may make the leaves yellow through lack of ions
- body mass is affected by genetics but also hugely influenced by diet
discontinuous variation
qualitative differences between phenotypes that have distincitive groups (e.g blood groups)
- caused by one gene
- genetic factors
continuous variation
quantitative differenced between phenotypes where there is a large range of variation within a population (e.g height)
- caused by lots of genes (polygenic)
- environmental factors
how does meiosis lead to genetic variation?
- crossing over in prophase I
- independent assortment - metaphase I and II
- random mutations
- the random fusion of gametes at fertilisation
stabilising selection
- eliminates extremes in a population
- favours the most normal or common individuals
- occurs with unchanging environmental conditions
directional selection
- favours individuals at the extreme in a range of variation
- changes characteristics of a population
- occurs due to a change in the environment
genetic drift
the random change in allele frequency in a population, some alleles are passed on and some disappear.
genetic bottleneck
a chance event causes a dramatic reduction in the size of population and the gene pool - can have a big effect on the allele frequency
founder effect
the loss of genetic variation due to the establishment of a new population by a very small number of individuals from a much larger population.
speciation
evolution of a new species from an existing one
sympatric speciation
speciation from reproductive isolation mechanism with no physical barrier
examples of sympatric speciation
- a change in courting behaviour
- polyploidy (mutation affecting whole sets of chromosomes)
- hybrid sterility ( a species formed from mating of two species is reproductively isolated if it is sterile)
allopatric speciation
speciation from geographical barriers, such as oceans, rivers, mountains and deserts
process of allopatric speciation
two populations of the same species are isolated for a time they may experience different environmental conditions
this will lead to the selection of different alleles in the two populations
gene pools become to different that if they are ever reunited, they would not be able to successfully breed together
chi squared test
used to compare observed results from genetic crosses with the predicted outcomes
what does it mean if the value of chi squared is smaller than the critical value?
then the difference between the observed and expected data is not statistically significant
assumptions made when using the Hardy-Weinburg principle
- large population
- random mating
- no mutation, genetic drift, migration
- no selective advantage for any genotype
hardy weinburg principle
p + q = 1
p^2 + 2pq + q^2 = 1
artificial selection
humans select organisms with desired characteristics and allow them to breed together.
this is repeated over many generations
this influences the evolution of a population over time
inbreeding
breeding of closely related individuals
problems caused by inbreeding
- limiting the gene pool reduces the chance of organisms evolving and adapting to changes in the environment
- more chance of being affected by recessive genetic disorders due to being so closely related
monogenetic crosses
investigate the inheritance of alleles of a single gene.
dihybrid crosses
investigate the inheritance of two separate genes on different chromosomes
epistasis
genes at one locus interact with genes at another locus by masking or supressing their expression
ratios for epistasis
recessive - 9:3:4 / 9:7
dominant - 12:3:1 / 13:1
linkage
occurs when genes for different characteristics found at different loci on the same chromosome sre inherited together
sex linkage
occurs when the genes are on the sex chromosomes, X and Y
why can men not be carriers of sex linked diseases?
they only have one X chromsome so cannot by heterozygous - they either have the disease or they do not
autosomal linkage
occurs when the genes are on the same chromosome - inherited together
codominance
both alleles are expressed in a phenotype of a heterozygote
allele
a form of a gene
why does autosomal linkage reduce variation?
pairs of alleles are inherited together
arguments against artificial selection
- inbreeding depression
- organisms may be less biologically fit, and have significant health problems
- organisms may have a shorter lifespan
- organisms may be less able to reproduce
responses to arguments against artificial selection
- gene banks can be used to reduce inbreeding risks, producing hybrid vigour
- genetic profilling of breeding individuals can reduce risks
- people may argue that domesticated animals are well cared for
- benefits to society may outweigh disadvantages (e.g greater yields of milk or meat)
why may be it be inappropiate to use the hardy weinburg principle to estimate allele frequencies in some investigatons
- if population is not subject to speciation
- if the population is too small
why is sexual reproduction of bacteria more likely to happen in the winter?
cold conditions - not optimum for offspring
how do the combined effects of meisosis and fertilisation ensure that the same parents can have highly varied offspring
- crossing over of homologous chromosomes, during prophase 1 (chromosomes swap genetic material)
- independent assortment oh homologoous chromosomes during metaphase/anaphase 1
- again in metaphase and anaphase II
- random fertilisation of egg cell by a sperm cell to create a zygote
