10 — genetics and evolution Flashcards
outline how reproductive isolation can occur in an animal population (3)
- can be sympathetic or allopathic
- temporal isolation by members of difference populations reproducing at different times
- behavioural isolation by difference in courtship behaviours
- geographic isolation by a population being separated by natural barriers to contact
outline the process of speciation (4)
- speciation is the splitting of a species into 2 species
- productive isolation/ lack of interbreeding
- isolation due to geography/ reproductive behaviour/ reproductive timing
- gene pools separated
- differences in traits cause gene pools to change/ diverge
- speciation changes accumulating over long periods
list two causes of variation within a gene pool (2)
- sexual reproduction/ random fertilisation/ meiosis
- mutation
describe how variation contributes to evolution by natural selection (3)
- variation is different phenotypes/ differences between individuals in a population/ species
- struggle for survival
- some individuals have advantageous characteristics have greater chance of survival
- favourable alleles passed on to next generation
outline what is required for speciation to occur (3)
- divided species/ gene pool
- reproductive isolation
- may be due to temporal/ behavioural/ geographic isolation
- different natural selection
starting from the concept of gene pool, explain briefly now populations of early vertebrates could have evolved into different groups (3)
- gene pool is all genes/ all alleles
- geographic/ temporal/ behavioural isolation
- speciation if populations are reproductively isolated
- in different environments there are different selection pressures
- allele frequencies change
starting from the concept of gene pool, explain briefly how populations of early vertebrates could have evolved into different groups (3)
- gene pool is all genes/ all alleles
- geographic/ temporal/ behavioural isolation
- speciation/ gene pool split if populations are reproductively isolated
- in different environments there are different selection pressures/ opportunities
- allele frequencies change
define the term polygenic inheritance (1)
- character affected by two or more genes
outline, with examples, different types of inheritance that produce non-Mendelian ratios (4)
- some traits may involve many genes
- linked genes on the same chromosome
- small numbers of recombinant phenotypes due to crossing over between linked genes
- codominance of specific alleles
- sex linked effects
- environmental influence on inheritance
explain the cause of sickle cell anaemia and how this disease affects humans (8)
- caused by a single nucleotide
- mutation of a gene of a subunit of hemoglobin
- mRNA copies the mutation of DNA and substitutes an amino acid in hemoglobin
- glutamic acid is substituted by valine
- sickle cell anemia involves distorted hemoglobin protein
causes sickling of red blood cells - block capillaries
- sickled red blood cells cannot carry enough oxygen for the body
- homozygous state causes severe anaemia
- heterozygous state only affected at high altitude
- heterozygous state provides protection against malaria parasite
explain how observation of the fossil record provides evidence for evolution (4)
- fossils show the types of organisms that lived in the past
- fossils can provide direct or indirect evident left in layers of rocks
- fossils can be dated by radioisotope dating of the rocks that hold them
- the sequence in which fossils appear matches the sequence in which species evolved
- sequences of fossils show progressive change over time
- increase in complexity of structures over time
- other extinct group in the fossil record suggest that organisms change over time
outline how experiments into inheritance can be performed using fruit flies and what has been discovered by carrying out such experiments (4)
- cross fruit flies with a certain trait with females of another characteristic
- analyse offspring of the cross
- dihybrid crosses
- discovered sec linkage
- ratios are different for males and females
- discovery of non mendelian ratios
- autosomal linkage
- fruit flies useful in inheritance experiments due to short life cycle
describe the methods used in cladistics and how evidence gained from this research can be utilised (7)
- study DNA of the same gene is different species
- study the amino acid sequence of the same protein in different species
- deduce which organisms are part of a clade
- use similarities and differences in sequence to construct a clad organ
- clad organ shows the most probable sequence of divergence of a clade
- deduce evolutionary origins
- numbers of base differences help deduce time since precise diverged
- deduce closeness of relationships according to similarities in bases
- used to help classify groups of organisms
- shows how closely humans are related to other primates
- has caused changes to classification of the figwort family
- distinguishing between homologous and analogous structures led to mistakes in classification
outline the changes to chromosomes that occur during prophase in the first division of meiosis (4)
- pairing of homologous chromosomes form bivalents
crossing over - exchange of DNA between chromatids
- new combination of alleles generated
- condensation of chromatids
- formation of a chiasma where crossing over occurred
explain the effects that the environment can have on DNA in living organisms (4)
mutation
- environment can cause mutation
- mutations are base sequence changes
- radiation can cause mutations
- mutagenic chemicals can cause mutations
epigenetics
- environment can cause changes to gene expression
- methylation in DNA changed in response to environmental factors
- methylation inhibits gene transcription
- body temperature can affect gene expression
outline how adaptive radiation provides evidence for evolution (3)
- diversification produced form a common ancestor
- homologous features have similarities of structure
- despite different functions
- different adaption to different selective pressures
- pentadactyl limbs
describe polyploidy and how it can lead to speciation (5)
- polyploidy is having more than two complete sets of chromosomes
- can be due to errors in meiosis
- can be due to DNA replication without cytokinesis
- polyploidy causes reproductive isolation
- diploids crossed with tetraploids produce infertile offspring
- tetraploids are therefore a new species
- infertile interspecific hydrides can become fertile by becoming polyploid
explain how a newly discovered plant species would be classified and named (7)
naming
- given a binomial name
- first name is genus and second name is species
- names are international
classification
- study the characteristics/ structure/ reproduction/ chemical properties/ DNA of the plant
- classify the plant in a group with other similar species
- natural classification corresponds with evolution
- analogous features should not be used
- hierarchy of groups
- a clade is a group of organisms evolved form a common ancestors
- base sequences used to group organisms into clades
- cladograms show the relationships between clades
- each branch point represents where species are formed via divergent evolution
- species now classified into a sequence of clades
explain how speciation occurs, including the different processes of isolation and selection (7)
- species is a group of organisms that interbreed and produce fertile offspring
- within an interbreeding population there is variety
- some adaptations favour survival to reproductive age
- alleles for these adaptations become more requiert
- speciation is the formation of new species
- occurs because populations have become reproductively isolated
- behavioural isolation involves differences in courtship or mating behaviours
- temporal isolation involves differences in the timing of courtship or mating behaviours
- geographic isolation refers to the physical barriers that exist that keep two populations from mating
- polyploidy can lead to reproductive isolation
- stabilising selection is when the two extremes of a trait have lower reproductive fitness
- directional selection is when one extreme of the trait has lower reproductive fitness
- disruptive selection favours both extreme phenotypes
distinguish between continuous and discrete variation, using examples (4)
continuous
- no distinct categories
- polygenic
- environmental influences
- e.g. weight/ height
discrete
- distinct categories
- few influencing genes
- not influenced by environment
- e.g. blood groups
explain how natural selection can lead to speciation (7)
- variation required for natural selection in populations
- mutation/ meiosis/ sexual reproduction is a source of variation
- competition
- adaptations make individuals suited to their environment
- survival of better adapted individuals
- inheritance of traits
- speciation is formation of a new species
- reproductive isolation of separated populations
- geographic isolation of populations can lead to speciation
- behavioural isolation of populations can lead to speciation
- disruptive selection between populations can lead to speciation
- gradual divergence of populations due to natural selection
- changes in the gene pools
- interbreeding becomes impossible
explain how polyploidy occurs and, using a named example, how polyploidy can lead to speciation (7)
- polyploidy is having more than two set of homologous chromosomes
- triploid has three sets
- tetraploid has four sets
- e.g. mules
- mules are triploid
- nondisjunction during meiosis
- diploid gamete can lead to polyploidy
- fusion of diploid and haploid gamete produces triploid cells
- DNA replication but no subsequent mitosis doubles the chromosome number
- polyploid crossed with non polyploid produces infertile offspring
- meiosis fails in triploid because chromosomes cannot pair up
- polyploid individuals are reproductively isolated
- speciation by polyploidy is common in plants
- polyploid individuals tend to be larger
describe the inheritance of red-green colorblindness (3)
- sex linked gene
- allele is recessive
- heterozygous females are unaffected
- XB denotes normal allele Xb denotes colour blindness allele
- more frequent in makes because they only have one X chromosome
- 50% of colour blindness in sons whose mother is heterozygous
outline adaptive radiation (5)
- happens in a group of species that evolve from a common ancestor
- evolution of a structure in different ways
- for different functions
- common features remain
- homologous structures are evidence of adaptive radiation
- adaptive radiation e.g. darwin’s finches
